Electropolishing is one of the oldest electrochemical techniques which is widely adapted in industry. Since many years electropolishing has been growing and from day to day it fills more and more niches in different fields of science and technology. Among possible Surface Treatments, electropolishing occupies a key role, because it is the cleanest way for removing hundreds of microns of material. Most galvanic processes start their life from water solutions. Electropolishing is not an exception, even now Nb electropolishing based on water solution with sulfuric and hydrofluoric acids is the most used. Literature results with this standard mixture are excellent,
however the EP of thousands of cavities could become an industrial nightmare from the point of view of security at work. HF is not like other highly corrosive acids: if, by accident, it gets in contact with skin, pain is not felt, but F- ions begin to pass through, searching for the bone calcium.
Since many years world’s science has been interested in ionic liquids and it is not for nothing. A green chemistry based on ionic liquids has come to the fore, and at INFN-LNL laboratories was done the first Niobium electropolishing by a harmless mixture of Choline Chloride and urea heated around 150°C.
In my work I will try to study influence of adding to the mixture some regulators. While it has already been showed the possibility of Nb dissolving with electropolishing effect,I will try to find recipe for technological Nb electropolishing. My second goal is to have ready a
recipe to application on 6 GHz cavities.
Fundamental Processes in Organic and Hybrid Solar Cellsdisorderedmatter
Invited talk at the LHP15 / Soltech Meeting at Kloster Banz, Germany
- photogeneration in model system for organic solar cells (pBTTT:PCBM)
- charge carrier recombination in phase separated organic blends by kinetic Monte Carlo simulations
- radiative efficiency and electrooptical reciprocity in organic-inorganic perovskite solar cells
- nongeminate
Nuclear damage parameters for SiC composites in fusion systemSURESH BHAISARE
The document discusses nuclear damage parameters for silicon carbide/silicon carbide (SiC/SiC) composites for use as structural materials in fusion reactor systems. It finds that:
1) The helium/dpa ratio is significantly higher in fusion reactors than fission reactors due to the harder neutron spectrum in fusion. This effect is more pronounced for SiC.
2) SiC/SiC composites are being considered for use in first walls, blankets, and other components due to their properties. However, lifetime is a major issue due to effects of radiation on the fiber, matrix, and interfaces.
3) Calculations were performed to determine dpa, helium production, hydrogen
This document describes current injection induced terahertz emission from 4H-SiC p-n junctions. The emission is attributed to intracenter optical transitions in nitrogen donor centers in the n-type region of the SiC p-n junction. When a current is injected, non-equilibrium carriers are injected into the n-region, initiating radiative transitions within the nitrogen donor centers. Emission peaks were observed that match the known energy levels of optical transitions in nitrogen donors. At 100 K and 300 mA, an output power of 58 μW was measured from a 3 mm2 device surface. This demonstrates that terahertz emitting devices can be made from simple SiC p-n junction structures with reasonable output powers and
Phillips - Atomic Layer Deposition of NbN Thin Films for Superconducting Radi...thinfilmsworkshop
http://www.surfacetreatments.it/thinfilms
Atomic Layer Deposition of NbN thin films for SRF applications (Larry Phillips - 15')
Speaker: Larry Phillips - Jefferson Lab - Newport News - Virginia | Duration: 15 min.
Abstract
Niobium Nitride is a 17K superconductor investigated since early eighthies for Superconducting Radiofrequency applications.
Atomic Layer deposition is instead a technique that only recently starts to be considered for industrial applications.
Mahadevan krishnan coaxial energetic deposition of thin filmsthinfilmsworkshop
AASC has been studying thin film coating of Nb on coupon substrates as well as on1300MHz RF cells. At the last Thinfilm workshop in Padua, we reported on high RRR measurements and good crystallinity in Nb films coated onto crystal substrates such as a-sapphire, MgO and also on polished Copper coupons. Since then, we have coated several 1300MHz RF cells provided to us and tested by LANL, ANL and JLab. The Qo vs. E measurements suggest that better surface preparation is a must for high quality RF performance. Future work will coat Copper cells with different surface preparation (centrifugal barrel polishing and EP) and try to improve upon our preliminary results. Results from Nb films coated on to Al6061 coupons are encouraging and motivate coating of a barrel polished Aluminum RF cell. Recently AASC has embarked upon two new thinfilm coating projects: Nb on stainless steel bellows for SRF accelerators and Cu films on stainless steel tubes for high power RF Couplers. We are also collaborating with CERN to coat a Cu disk of a quadrupole resonator with Nb, for RF tests at high fields. This talk will provide details of all of these ongoing activities, all of which are supported by the US Department of Energy via SBIR contracts.
Rosa alejandra lukaszew tests of the gurenvich odel toward larger field gra...thinfilmsworkshop
SRF properties are inherently a surface phenomenon involving a material thickness of a few microns thus opening up the possibility of using thin film coatings to achieve a desired performance. I will describe our experimental attempts to test the superconducting/insulating/superconducting (SIS) multilayer model proposed by A. Gurevich [1] to shield the bulk of the cavity from vortex penetration and hence enable larger accelerating fields than presently possible.
This document is the dissertation of Zhang Yan for the degree of Ph.D. It summarizes his research on sputtering niobium films into RF cavities and sputtering of superconducting V3Si films. The dissertation contains 6 chapters that discuss sputtering techniques for niobium cavities, sputtering niobium films on an RFQ model, co-sputtering and reactive sputtering of V3Si films, and thermal diffusion of V3Si films. The research aimed to develop sputtering methods for producing superconducting coatings on RF cavities and investigate the properties of V3Si films for potential use in superconducting radio frequency applications.
The lowest possible surface resistivity and higher accelerating field are the paramount
considerations, hence are obligatory for accelerating cavities. Since, superconducting materials
are used to make radio-frequency cavities for future accelerators. In the case of rf cavities,
superconductors are being used in order to minimize the power dissipated and increase the
figures of merit of a radio-frequency cavity, such as the quality factor and accelerating gradient.
Hence, these could be achieved by improving surface treatment to the cavity, and processing
techniques must be analyzed in order to optimize these figures of merit.
The research work reported in this dissertation mainly carried out on tesla type seamless 6GHz
Nb and Cu cavities. We have developed two innovative techniques: firstly, for mechanical
polishing of cavities, and secondly for purification of these cavities at atmospheric pressure under
cover of 4Helium gas (for protection) and at ultra-high vacuum (UHV) system. These cavities are
fabricated by spinning technology to create seamless cavities.
The main advantages of 6 GHz bulk-Nb cavities are saving cost, materials and time to collect
statistics of surface treatments and RF test in a very short time scale. Cavities are RF tested
before and after high temperature treatment under atmospheric pressure (under cover of inert gas
atmosphere to protect inner and outer surface of cavity) inside transparent quartz tube, and under
UHV conditions. Induction heating method is used to anneal the cavity at temperatures higher
than 2000°C and close to the melting point of Nb for less than a minute while few seconds at
maximum temperature. Before RF test and UHV annealing, the surface treatment processes like
tumbling, chemical, electro-chemical (such as BCP and EP), ultrasonic cleaning and high
pressure rinsing (HPR) have been employed. High temperature treatment for few minutes at
atmospheric pressure allow to reduce hydrogen, oxygen and other elemental impurities, which
effects on cavity Q-factor degradation, hence recovers rf performances of these cavities. This
research work will address these problems and illustrate the importance of surface treatments.
Fundamental Processes in Organic and Hybrid Solar Cellsdisorderedmatter
Invited talk at the LHP15 / Soltech Meeting at Kloster Banz, Germany
- photogeneration in model system for organic solar cells (pBTTT:PCBM)
- charge carrier recombination in phase separated organic blends by kinetic Monte Carlo simulations
- radiative efficiency and electrooptical reciprocity in organic-inorganic perovskite solar cells
- nongeminate
Nuclear damage parameters for SiC composites in fusion systemSURESH BHAISARE
The document discusses nuclear damage parameters for silicon carbide/silicon carbide (SiC/SiC) composites for use as structural materials in fusion reactor systems. It finds that:
1) The helium/dpa ratio is significantly higher in fusion reactors than fission reactors due to the harder neutron spectrum in fusion. This effect is more pronounced for SiC.
2) SiC/SiC composites are being considered for use in first walls, blankets, and other components due to their properties. However, lifetime is a major issue due to effects of radiation on the fiber, matrix, and interfaces.
3) Calculations were performed to determine dpa, helium production, hydrogen
This document describes current injection induced terahertz emission from 4H-SiC p-n junctions. The emission is attributed to intracenter optical transitions in nitrogen donor centers in the n-type region of the SiC p-n junction. When a current is injected, non-equilibrium carriers are injected into the n-region, initiating radiative transitions within the nitrogen donor centers. Emission peaks were observed that match the known energy levels of optical transitions in nitrogen donors. At 100 K and 300 mA, an output power of 58 μW was measured from a 3 mm2 device surface. This demonstrates that terahertz emitting devices can be made from simple SiC p-n junction structures with reasonable output powers and
Phillips - Atomic Layer Deposition of NbN Thin Films for Superconducting Radi...thinfilmsworkshop
http://www.surfacetreatments.it/thinfilms
Atomic Layer Deposition of NbN thin films for SRF applications (Larry Phillips - 15')
Speaker: Larry Phillips - Jefferson Lab - Newport News - Virginia | Duration: 15 min.
Abstract
Niobium Nitride is a 17K superconductor investigated since early eighthies for Superconducting Radiofrequency applications.
Atomic Layer deposition is instead a technique that only recently starts to be considered for industrial applications.
Mahadevan krishnan coaxial energetic deposition of thin filmsthinfilmsworkshop
AASC has been studying thin film coating of Nb on coupon substrates as well as on1300MHz RF cells. At the last Thinfilm workshop in Padua, we reported on high RRR measurements and good crystallinity in Nb films coated onto crystal substrates such as a-sapphire, MgO and also on polished Copper coupons. Since then, we have coated several 1300MHz RF cells provided to us and tested by LANL, ANL and JLab. The Qo vs. E measurements suggest that better surface preparation is a must for high quality RF performance. Future work will coat Copper cells with different surface preparation (centrifugal barrel polishing and EP) and try to improve upon our preliminary results. Results from Nb films coated on to Al6061 coupons are encouraging and motivate coating of a barrel polished Aluminum RF cell. Recently AASC has embarked upon two new thinfilm coating projects: Nb on stainless steel bellows for SRF accelerators and Cu films on stainless steel tubes for high power RF Couplers. We are also collaborating with CERN to coat a Cu disk of a quadrupole resonator with Nb, for RF tests at high fields. This talk will provide details of all of these ongoing activities, all of which are supported by the US Department of Energy via SBIR contracts.
Rosa alejandra lukaszew tests of the gurenvich odel toward larger field gra...thinfilmsworkshop
SRF properties are inherently a surface phenomenon involving a material thickness of a few microns thus opening up the possibility of using thin film coatings to achieve a desired performance. I will describe our experimental attempts to test the superconducting/insulating/superconducting (SIS) multilayer model proposed by A. Gurevich [1] to shield the bulk of the cavity from vortex penetration and hence enable larger accelerating fields than presently possible.
This document is the dissertation of Zhang Yan for the degree of Ph.D. It summarizes his research on sputtering niobium films into RF cavities and sputtering of superconducting V3Si films. The dissertation contains 6 chapters that discuss sputtering techniques for niobium cavities, sputtering niobium films on an RFQ model, co-sputtering and reactive sputtering of V3Si films, and thermal diffusion of V3Si films. The research aimed to develop sputtering methods for producing superconducting coatings on RF cavities and investigate the properties of V3Si films for potential use in superconducting radio frequency applications.
The lowest possible surface resistivity and higher accelerating field are the paramount
considerations, hence are obligatory for accelerating cavities. Since, superconducting materials
are used to make radio-frequency cavities for future accelerators. In the case of rf cavities,
superconductors are being used in order to minimize the power dissipated and increase the
figures of merit of a radio-frequency cavity, such as the quality factor and accelerating gradient.
Hence, these could be achieved by improving surface treatment to the cavity, and processing
techniques must be analyzed in order to optimize these figures of merit.
The research work reported in this dissertation mainly carried out on tesla type seamless 6GHz
Nb and Cu cavities. We have developed two innovative techniques: firstly, for mechanical
polishing of cavities, and secondly for purification of these cavities at atmospheric pressure under
cover of 4Helium gas (for protection) and at ultra-high vacuum (UHV) system. These cavities are
fabricated by spinning technology to create seamless cavities.
The main advantages of 6 GHz bulk-Nb cavities are saving cost, materials and time to collect
statistics of surface treatments and RF test in a very short time scale. Cavities are RF tested
before and after high temperature treatment under atmospheric pressure (under cover of inert gas
atmosphere to protect inner and outer surface of cavity) inside transparent quartz tube, and under
UHV conditions. Induction heating method is used to anneal the cavity at temperatures higher
than 2000°C and close to the melting point of Nb for less than a minute while few seconds at
maximum temperature. Before RF test and UHV annealing, the surface treatment processes like
tumbling, chemical, electro-chemical (such as BCP and EP), ultrasonic cleaning and high
pressure rinsing (HPR) have been employed. High temperature treatment for few minutes at
atmospheric pressure allow to reduce hydrogen, oxygen and other elemental impurities, which
effects on cavity Q-factor degradation, hence recovers rf performances of these cavities. This
research work will address these problems and illustrate the importance of surface treatments.
International Committee for Future Accelerators recommended that the Linear Collider design has to be based on the superconducting technology. And this is the reason why the international scientific society directed efforts to improving superconductive technology and reducing its cost.
In this work, in the framework of researching a valid alternative to Nb for RF superconducting cavities, thin film Nb3Sn has been investigated. The goal will be the achievement of superconducting cavities working better than the Nb ones at 4.2 K.
In order to improve the existing technology of substrates coating by thermally diffused Nb3Sn a new high temperature annealing technology has been developed. In the first part of the work, is given the short theoretical review of RF superconductivity, main superconductors that are used to be a good alternative to a pure Nb and fundamentals of the induction heating theory. Second part is dedicated to the existing double furnace technology, developed in the superconductivity lab in LNL. The influence of preliminary surface treatments like glow discharge of the sample, anodization and chemical etching on the quality of thermally diffused Nb3Sn was studied. And in the third part is given the description of the new induction heating system, suggested for annealing of the 6 GHz cavities. Also in the third part we will go through the results of coating samples and cavities with thermally diffused Nb3Sn with high temperature annealing and the results of the RF – test.
Finally, it is important to mention, that from the very beginning of investigation the induction heating for annealing 6 GHz cavities it became clear that the technology has an enormous potential in producing thermally diffused Nb3Sn.
Preparation of cavity walls has been one of the major problems in superconducting radio-frequency (SRF) accelerator technology. Accelerator performance depends directly on the physical and chemical characteristics at the SRF cavity surface.
The ambitious objective of this project is to study a cavity surface preparation process which is superior in terms of cost, performance, and safety, to the wet chemical process currently in use. Plasma based processes provide an excellent opportunity to achieve these goals.
Plasmas are chemically active media. Depending on the way they are activated and their working power, they can generate low or very high "temperatures" and are referred correspondingly as cold or thermal plasmas. This wide temperature range enables various applications for plasma technologies: surface coatings, waste destruction, gas treatments, chemical synthesis, machining ... many of these techniques have been industrialized.
A large number of important industrial plasma applications are carried out close to atmospheric pressure, in many cases in atmospheric air.
The fascinating possibility to perform cleaning and/or etching processes of RF cavities without the need of any vacuum pumping system has to be deeply explored realizing different atmospheric congurations as corona plasma, rf resonance plasma, plasma jet and torch.
Thermal plasmas (especially arc plasma) were extensively industrialized, principally by aeronautic sector. Cold plasma technologies have been developed in the microelectronics but their vacuum equipment limits their implantation.
To avoid drawback associated with vacuum, several laboratories have tried to transpose to atmospheric pressure processes that work under vacuum for the moment. Their researches have led to various original sources.
In the textile sector, a number of plasma applications are conceivable and some have been tested in laboratory scale. The chemical functionality and/or the morphology of a ber surface can be altered in order to improve very dierent properties to tailor them for
certain demands. The wettability can be increased to achieve a better impregnation or a deeper dying or, in contrast; it also can be decreased to create a water repellent behavior.
New chemical functionalities on the surface can promote the reactivity with dyes. The water free removal of sizings seems to be possible. These are only a few examples that demonstrate the potential of this technology.
We decided to try to ignite a resonance atmospheric plasma into 1.5 GHz superconducting niobium cavities to perform a feasibility study. The second step has been the attempt to understand what really happens to the resonant structure internal surface. The most powerful tool consists in the atmospheric plasma treatment and fast rf characterization of 6 GHz small resonators.
A seminar report summarizes carbon nanotubes, including their synthesis, types, and applications. It describes three main methods for synthesizing carbon nanotubes: plasma-based methods such as arc discharge; thermal methods such as chemical vapor deposition; and hydrothermal methods. It outlines the different types of carbon nanotubes including single-walled, multi-walled, nanotori, nanobuds, and nanonorns. Current applications discussed include materials, electronics and energy storage, with potential future applications in fields like biotechnology.
The document summarizes a student's final project to design and construct a low pressure capacitively coupled plasma etcher. Key points:
- The objective was to design a plasma etch source that can hold a vacuum and create a stable plasma for etching.
- The initial design was simplified using aluminum and graphite electrodes. The final design maintained the materials due to cost but added insulation on the electrodes.
- Construction involved machining parts and assembling the chamber, which was then tested and optimized by addressing leaks and plasma instability issues.
- Diagnostics using optical emission spectroscopy were planned to analyze the plasma properties and etch species.
- Future work proposed improving the design and experimenting with
This works deals with the A15 compound synthesis on niobium samples and over the
internal surface of niobium cavities by means of induction heating. Specifically, three compounds were studied: Nb3Ga, Nb3Al and Nb-Al-Ga. As for the preparation of the niobium samples, they were treated with BCP solution in order to polish the surface. The niobium cavities were treated with centrifugal tumbling, BCP solution and high pressure water rising. Subsequent, the samples, or cavities, were placed into an inductor controlling the voltage, time, sample position, temperature, type and pressure of gas used. The highest critical temperature
obtained was 18 K and Tc 0,35 K, in Nb-Al-Ga#1 sample by inductive measurement.
Mapping analysis showed the uniform diffusion of aluminum into the niobium, and the gallium diffuses creating channels into niobium. The composition was measured by EDS obtaining (82±1)% wt. Niobium, (11,3±0,9)% wt. Gallium, (4,7±0,2)% wt. Aluminum and (1,9±0,1)% wt. Oxygen. Finally, RF test confirmed that the cavities obtained after the annealing were normal conductive indicating that the preparation parameters must still be optimized.
Particle physics is now at the threshold of great discoveries. The experiments with particle accelerators and observations of the cosmos have focused attention on phenomena that can not be explained by the standard theory. The technology based on superconducting niobium accelerating cavities can reach a high expenditure of energy by many orders of magnitude lower than that of normal-conducting copper cavities. Even taking into account the power spent to maintain the temperature of liquid helium, the net gain in economic terms is still unassailable.
The sputtering technology was chosen first in the pure diode configuration and subsequently in the magnetron configuration. High Power Impulse Magnetron Sputtering (HIPIMS) is an evolution of the magnetron technique which relies on 100μs high voltage pulses of the order of 1 kV compared to the 300 V of the standard DC magnetron process. During the pulse a huge power density is deposited onto the target, of the order of a few kW/cm2 compared to a few W/cm2 of the standard DC process, producing a highly dense plasma in which also the Nb atoms are partially ionized. These can in turn be attracted to the substrate with a suitable bias. A further advantage of the technique lies in the fact that no hardware changes are required compared to a standard DC biased magnetron system, except for the obvious replacement of the power supply.
In this work, an R&D effort has been undertaken to study the HIPIMS, to improve it and understand the correlation between the parameters applied and the film morphology, the superconducting properties and the RF film quality.
The experiment system is based on the NEW HIGH-RATE SYSTEM for the deposition cavity 1.5 GHz. The experimental details and the measurements of the characteristics of the deposited films are described. Even though the work is still in progress, all of the partial results from now on have been analyzed and commented, in order to extrapolate all the information. The final results are a global overview of the HIPIMS techniques for Nb on 1.5Hz superconducting cavity. Suggestions for future efforts have been included as part of the conclusions.
This document describes an investigation of the LaAlO3-SrTiO3 (LAO-STO) heterointerface using transmission electron microscopy (TEM). The sample was prepared using pulsed laser deposition to grow a thin film of LAO on a STO substrate, followed by ion slicing to produce a wedge-shaped cross-section for TEM analysis. The TEM results revealed a high-density two-dimensional electron gas formed at the LAO-STO interface, which has potential applications in next-generation electronic devices and holds promise for novel electronic properties.
This document provides an introduction to carbon nanotubes, including their potential applications. It discusses how carbon nanotubes can be used structurally in combat jackets, bridges, and for a proposed space elevator due to their high tensile strength. Electromagnetically, carbon nanotubes show promise for use in artificial muscles, displays, transistors, and conductive films. They may also help filter water and air more efficiently than current methods, and store hydrogen for fuel cells. The document outlines how carbon nanotubes could replace conventional computer memory and be used in golf balls and bicycles to enhance performance.
The superconductor accelerator cavity is one of the most important and perspective technology for an advance accelerator. For example, the International Committee for Future Accelerators decided that the Linear Collider design had been based on the superconductor technology. Moreover, the accelerator operating with continue wave (CW) mode must use the superconductor technology in stead of the normal conductor technology, such as the Accelerator-driven sub-critical reactor system (ADS), the Accelerator Transmutation of Waste (ATW), the Accelerator Production of Tritium (APT), and so on.
In order to meet all kinds of application, the scientific world interest is now focus on further developments of new resonant cavities fabrication techniques to reduce cost and improve the performance of the accelerator cavity. To realize this object, one of the important methods is to pursue research on new materials. The goal will be the achievement of superconducting cavity working better the Nb ones at 4.2K. For example, the better parameters of the Tc, the surface resistance, the critical field Hc and the Q value are needed.
Up to now, the most possible candidate is Nb3Sn. The Nb3Sn has not only the better superconductivity parameters, but also the stable property and the easy fabrication. There are two methods to fabricate the superconductor cavity with the Nb3Sn, which are including the diffusion method and the multilayer deposition method. In the thesis, we focus on the multilayer deposition method, and ......
Bubble power . good for the environment safetyThyaguThyag
This document summarizes a seminar presentation on bubble power and sonofusion as a potential new energy source. It describes how sonofusion works by using a piezoelectric crystal to generate intense sound waves in a flask of deuterated acetone, removing naturally occurring gas bubbles via vacuum pump, and firing a pulsed neutron generator precisely when pressure is lowest to initiate fusion reactions within acoustic bubbles. The document outlines basic requirements, applications, challenges, and concludes that sonofusion is a potentially self-sustaining and environmentally friendly energy source, though independent replication of initial results is still needed.
Can we just imagine of having a TV which can be rolled up? Wouldn’t you like to be able to read off the screen of your laptop in direct sunlight? Your mobile phone battery to last much, much longer? Or your next flat screen TV to be less expensive, much flatter, and even flexible? Well, now it is possible by an emerging technology based on the revolutionary discovery that, light emitting, fast switching diode could be made from polymers as well as semiconductors.OLED
This document discusses carbon nanotubes (CNTs), including their discovery, structure, properties, synthesis, applications, and future potential. Some key points:
- CNTs were discovered in 1991 and have a rolled-up graphene sheet structure that gives them unique mechanical and electrical properties.
- CNTs exhibit extraordinary strength and conductivity, with current-carrying capacity 1000 times higher than copper.
- Common synthesis methods are arc discharge, laser ablation, and chemical vapor deposition.
- Applications include energy storage, conductive composites, electronics, and more. Mass production is increasing and CNTs are already used in some products.
- CNTs show promise for applications across many industries
Optimal Generation of 254nm ultraviolet radiationIOSR Journals
Abstract: The science of the application of 254nm UV from mercury doped glow discharge tubes has been a major topic since Johann Ritter discovered UV via its chemical inducing reactions in 1801 and Niels Finsen’s 1860 work on UV therapy in treating rickets. In 1857 Siemens AG patented UV254nm creation via filamentary discharge, subsequently widely used for ozone production. By 1932 the Coblentz Congress had defined the three regions of the UV action spectrum. This paper presents the science of a new design for a sterilizer module fabricated from extruded, recycled aluminium. This novel design achieves better than D10 performance using six UV tubes per module driven by three electronic ballasts drawing a total current of only 1.26 amps at 240V single phase. This module delivers more than 45,000 microwatts per square centimetre of 254nm UV which sterilises one litre per second in a module with a dwell time of 1.6 seconds in a design with less than 0.5 bar pressure drop across each module. This system takes the electrical efficiency of 254 UV generation from less than 25% to more than 92% as measured by an NPL-traceable calibration against a current industry standard. Since 254nm UV generating tubes are also the basis of fluorescent lighting this new work on optimising the generation of 254nm UV also has application worldwide to improved efficiency of fluorescent tube electrical lighting, because we have shown that most of the fluorescent lamps operating today (particularly the T8 1” diameter) are running at less than 25% efficiency as opposed to the over 92% which is possible with the methods we describe. The work reported here shows that the Townsend equation for electron transport in glow discharge plasmas is not adequate since it does not address either plasma diameter or plasma drive frequency both of which fundamentally alter the electron energy transfer efficiencies to mercury atoms in the plasma.
This document summarizes an experiment investigating the ablation of dental hydroxyapatite using picosecond laser pulses. Key findings include:
- Picosecond laser pulses ablate dental enamel with no signs of thermal damage, unlike longer pulse durations.
- Spectroscopic analysis of the laser-induced plasma detected excitations of calcium and sodium, allowing distinction between healthy and carious tooth material.
- Estimates of plasma temperature and free electron density were obtained from the plasma spectra.
- Precise cavities were ablated in tooth enamel using a computer-controlled translation stage and laser system producing 30ps pulses at 1mJ energy.
This document reviews recent research on nanoscale thermal transport. It discusses how interfaces play an important role in heat transfer at the nanoscale, as the length scales are comparable to phonon mean free paths. Several experiments measuring the thermal conductance of model solid-solid interfaces are summarized. Molecular dynamics simulations are emerging as a powerful tool for studying phonon scattering and thermal conductivity at interfaces. However, fundamental questions remain regarding the definition of temperature in nonequilibrium nanoscale systems. The document goes on to discuss thermal transport in nanostructures, nanostructured materials, measurement techniques, and outlines remaining challenges in the field.
Approach To Power Harvesting With Piezoelectric MaterialIJERA Editor
Nowadays, most of the research in the energy field is to develop sources of energy for the future, With oil resources being over, tapped and eventually bound to end, it is time to find renewable Piezoelectric materials are being more and more studied as they turn out to be very unusual materials with very specific and interesting properties. In fact, these materials have the ability to produce electrical energy from mechanical energy, for example, they can convert mechanical behavior like vibrations into electricity. Recent work has shown that these materials could be used as power generators, the amount of energy produced is still very low, hence the necessity to optimize them. The objective of this work is to study the all of the piezoelectric material systems and calculated the possible power generated from it, and a special case to design and build a fully functional floor tile device that when stepped on will generate enough energy to light an LED, The system will be charge a temporary energy storage device, a capacitor bank, and then use this stored energy to power an LED.
Tor A Fjeldly and Muhammad Nawaz submitted a master's thesis on the formation of silicon nanostructures in silicon nitride thin films for use in solar cells. The goal was to develop silicon nitride anti-reflective coatings containing silicon nanoparticles and characterize the films using ellipsometry. Seven silicon nitride films with varying stoichiometry were deposited using PECVD and characterized with ellipsometry, photoluminescence, and transmission electron microscopy before and after annealing. Ellipsometry showed the films became more compact after annealing with increased refractive index. Photoluminescence was observed for samples with high ammonia flow but decreased after annealing, while samples with low ammonia flow showed little photolum
This document discusses a thesis project that aims to evaluate the radiation hardness of sensor materials for use in the proposed International Linear Collider beamline calorimeter (BeamCal). The author performs Monte Carlo simulations to estimate the shower conversion factor α, which quantifies the mean radiation fluence at a sensor per incident electron, as a function of electron energy. Analysis of the simulation data provides fluence distribution profiles that decrease radially from the center of the irradiated sensor area. The author accounts for sensor rastering across the electron beam, which provides even illumination over a 2 cm area. Observations from the simulations indicate the radiation fluence is linearly dependent on the incident electron energy.
This presentation summarizes history and recent development of perovskite solar cells. If you have any questions or comments, you can reach me at agassifeng@gmail.com
Potential enhancement of thermoelectric energy conversion in cobaltite superl...Anastasios Englezos
This document is a master's thesis submitted by Tasos Englezos investigating the potential enhancement of thermoelectric energy conversion in cobaltite oxide superlattices. The thesis aims to grow superlattices composed of alternating layers of NaxCoO3 and Ca3Co4O9 using pulsed laser deposition, as both materials show promise for thermoelectric applications but also have limitations. Characterization of the superlattices shows the structures maintain crystalline coherence while electrical and thermal properties are preserved at a good level. Further measurements of thermal conductivity are needed to determine if the superlattice approach reduces thermal conductivity and thereby improves thermoelectric efficiency in these cobaltite oxides.
There is no dubt that the subject of superconducting resonant cavities is a fascinating field both physical and engineering point of view.
The application of superconductivity to the world of resonant cavities has made achievable results unimaginable otherwise.
Independently of the special field of application, superconducting resonant circuits have superior performances compared to roo-temperatire circuits.
However the greatest resource of such devices stays not in the high quality of the results already obtained, but in all potential applications and new ideas that must be still developed.
When hearing about persistent currents recirculating for several year in a superconducting loop without any appreciable decay, we realize that we are dealing with a phenomenon wich in nature is the closest we know to the perpetual motion.
The zero resistivity and the perfect diamagnetism in Mercury at 4.2 K, the discovery of superconducting materials, finally the revolution of the "liquid Nitrogen superconductivity": Nature discloses drop by drop its intimate secrets.
Nobody can exclude that the final surpreise must still come.
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International Committee for Future Accelerators recommended that the Linear Collider design has to be based on the superconducting technology. And this is the reason why the international scientific society directed efforts to improving superconductive technology and reducing its cost.
In this work, in the framework of researching a valid alternative to Nb for RF superconducting cavities, thin film Nb3Sn has been investigated. The goal will be the achievement of superconducting cavities working better than the Nb ones at 4.2 K.
In order to improve the existing technology of substrates coating by thermally diffused Nb3Sn a new high temperature annealing technology has been developed. In the first part of the work, is given the short theoretical review of RF superconductivity, main superconductors that are used to be a good alternative to a pure Nb and fundamentals of the induction heating theory. Second part is dedicated to the existing double furnace technology, developed in the superconductivity lab in LNL. The influence of preliminary surface treatments like glow discharge of the sample, anodization and chemical etching on the quality of thermally diffused Nb3Sn was studied. And in the third part is given the description of the new induction heating system, suggested for annealing of the 6 GHz cavities. Also in the third part we will go through the results of coating samples and cavities with thermally diffused Nb3Sn with high temperature annealing and the results of the RF – test.
Finally, it is important to mention, that from the very beginning of investigation the induction heating for annealing 6 GHz cavities it became clear that the technology has an enormous potential in producing thermally diffused Nb3Sn.
Preparation of cavity walls has been one of the major problems in superconducting radio-frequency (SRF) accelerator technology. Accelerator performance depends directly on the physical and chemical characteristics at the SRF cavity surface.
The ambitious objective of this project is to study a cavity surface preparation process which is superior in terms of cost, performance, and safety, to the wet chemical process currently in use. Plasma based processes provide an excellent opportunity to achieve these goals.
Plasmas are chemically active media. Depending on the way they are activated and their working power, they can generate low or very high "temperatures" and are referred correspondingly as cold or thermal plasmas. This wide temperature range enables various applications for plasma technologies: surface coatings, waste destruction, gas treatments, chemical synthesis, machining ... many of these techniques have been industrialized.
A large number of important industrial plasma applications are carried out close to atmospheric pressure, in many cases in atmospheric air.
The fascinating possibility to perform cleaning and/or etching processes of RF cavities without the need of any vacuum pumping system has to be deeply explored realizing different atmospheric congurations as corona plasma, rf resonance plasma, plasma jet and torch.
Thermal plasmas (especially arc plasma) were extensively industrialized, principally by aeronautic sector. Cold plasma technologies have been developed in the microelectronics but their vacuum equipment limits their implantation.
To avoid drawback associated with vacuum, several laboratories have tried to transpose to atmospheric pressure processes that work under vacuum for the moment. Their researches have led to various original sources.
In the textile sector, a number of plasma applications are conceivable and some have been tested in laboratory scale. The chemical functionality and/or the morphology of a ber surface can be altered in order to improve very dierent properties to tailor them for
certain demands. The wettability can be increased to achieve a better impregnation or a deeper dying or, in contrast; it also can be decreased to create a water repellent behavior.
New chemical functionalities on the surface can promote the reactivity with dyes. The water free removal of sizings seems to be possible. These are only a few examples that demonstrate the potential of this technology.
We decided to try to ignite a resonance atmospheric plasma into 1.5 GHz superconducting niobium cavities to perform a feasibility study. The second step has been the attempt to understand what really happens to the resonant structure internal surface. The most powerful tool consists in the atmospheric plasma treatment and fast rf characterization of 6 GHz small resonators.
A seminar report summarizes carbon nanotubes, including their synthesis, types, and applications. It describes three main methods for synthesizing carbon nanotubes: plasma-based methods such as arc discharge; thermal methods such as chemical vapor deposition; and hydrothermal methods. It outlines the different types of carbon nanotubes including single-walled, multi-walled, nanotori, nanobuds, and nanonorns. Current applications discussed include materials, electronics and energy storage, with potential future applications in fields like biotechnology.
The document summarizes a student's final project to design and construct a low pressure capacitively coupled plasma etcher. Key points:
- The objective was to design a plasma etch source that can hold a vacuum and create a stable plasma for etching.
- The initial design was simplified using aluminum and graphite electrodes. The final design maintained the materials due to cost but added insulation on the electrodes.
- Construction involved machining parts and assembling the chamber, which was then tested and optimized by addressing leaks and plasma instability issues.
- Diagnostics using optical emission spectroscopy were planned to analyze the plasma properties and etch species.
- Future work proposed improving the design and experimenting with
This works deals with the A15 compound synthesis on niobium samples and over the
internal surface of niobium cavities by means of induction heating. Specifically, three compounds were studied: Nb3Ga, Nb3Al and Nb-Al-Ga. As for the preparation of the niobium samples, they were treated with BCP solution in order to polish the surface. The niobium cavities were treated with centrifugal tumbling, BCP solution and high pressure water rising. Subsequent, the samples, or cavities, were placed into an inductor controlling the voltage, time, sample position, temperature, type and pressure of gas used. The highest critical temperature
obtained was 18 K and Tc 0,35 K, in Nb-Al-Ga#1 sample by inductive measurement.
Mapping analysis showed the uniform diffusion of aluminum into the niobium, and the gallium diffuses creating channels into niobium. The composition was measured by EDS obtaining (82±1)% wt. Niobium, (11,3±0,9)% wt. Gallium, (4,7±0,2)% wt. Aluminum and (1,9±0,1)% wt. Oxygen. Finally, RF test confirmed that the cavities obtained after the annealing were normal conductive indicating that the preparation parameters must still be optimized.
Particle physics is now at the threshold of great discoveries. The experiments with particle accelerators and observations of the cosmos have focused attention on phenomena that can not be explained by the standard theory. The technology based on superconducting niobium accelerating cavities can reach a high expenditure of energy by many orders of magnitude lower than that of normal-conducting copper cavities. Even taking into account the power spent to maintain the temperature of liquid helium, the net gain in economic terms is still unassailable.
The sputtering technology was chosen first in the pure diode configuration and subsequently in the magnetron configuration. High Power Impulse Magnetron Sputtering (HIPIMS) is an evolution of the magnetron technique which relies on 100μs high voltage pulses of the order of 1 kV compared to the 300 V of the standard DC magnetron process. During the pulse a huge power density is deposited onto the target, of the order of a few kW/cm2 compared to a few W/cm2 of the standard DC process, producing a highly dense plasma in which also the Nb atoms are partially ionized. These can in turn be attracted to the substrate with a suitable bias. A further advantage of the technique lies in the fact that no hardware changes are required compared to a standard DC biased magnetron system, except for the obvious replacement of the power supply.
In this work, an R&D effort has been undertaken to study the HIPIMS, to improve it and understand the correlation between the parameters applied and the film morphology, the superconducting properties and the RF film quality.
The experiment system is based on the NEW HIGH-RATE SYSTEM for the deposition cavity 1.5 GHz. The experimental details and the measurements of the characteristics of the deposited films are described. Even though the work is still in progress, all of the partial results from now on have been analyzed and commented, in order to extrapolate all the information. The final results are a global overview of the HIPIMS techniques for Nb on 1.5Hz superconducting cavity. Suggestions for future efforts have been included as part of the conclusions.
This document describes an investigation of the LaAlO3-SrTiO3 (LAO-STO) heterointerface using transmission electron microscopy (TEM). The sample was prepared using pulsed laser deposition to grow a thin film of LAO on a STO substrate, followed by ion slicing to produce a wedge-shaped cross-section for TEM analysis. The TEM results revealed a high-density two-dimensional electron gas formed at the LAO-STO interface, which has potential applications in next-generation electronic devices and holds promise for novel electronic properties.
This document provides an introduction to carbon nanotubes, including their potential applications. It discusses how carbon nanotubes can be used structurally in combat jackets, bridges, and for a proposed space elevator due to their high tensile strength. Electromagnetically, carbon nanotubes show promise for use in artificial muscles, displays, transistors, and conductive films. They may also help filter water and air more efficiently than current methods, and store hydrogen for fuel cells. The document outlines how carbon nanotubes could replace conventional computer memory and be used in golf balls and bicycles to enhance performance.
The superconductor accelerator cavity is one of the most important and perspective technology for an advance accelerator. For example, the International Committee for Future Accelerators decided that the Linear Collider design had been based on the superconductor technology. Moreover, the accelerator operating with continue wave (CW) mode must use the superconductor technology in stead of the normal conductor technology, such as the Accelerator-driven sub-critical reactor system (ADS), the Accelerator Transmutation of Waste (ATW), the Accelerator Production of Tritium (APT), and so on.
In order to meet all kinds of application, the scientific world interest is now focus on further developments of new resonant cavities fabrication techniques to reduce cost and improve the performance of the accelerator cavity. To realize this object, one of the important methods is to pursue research on new materials. The goal will be the achievement of superconducting cavity working better the Nb ones at 4.2K. For example, the better parameters of the Tc, the surface resistance, the critical field Hc and the Q value are needed.
Up to now, the most possible candidate is Nb3Sn. The Nb3Sn has not only the better superconductivity parameters, but also the stable property and the easy fabrication. There are two methods to fabricate the superconductor cavity with the Nb3Sn, which are including the diffusion method and the multilayer deposition method. In the thesis, we focus on the multilayer deposition method, and ......
Bubble power . good for the environment safetyThyaguThyag
This document summarizes a seminar presentation on bubble power and sonofusion as a potential new energy source. It describes how sonofusion works by using a piezoelectric crystal to generate intense sound waves in a flask of deuterated acetone, removing naturally occurring gas bubbles via vacuum pump, and firing a pulsed neutron generator precisely when pressure is lowest to initiate fusion reactions within acoustic bubbles. The document outlines basic requirements, applications, challenges, and concludes that sonofusion is a potentially self-sustaining and environmentally friendly energy source, though independent replication of initial results is still needed.
Can we just imagine of having a TV which can be rolled up? Wouldn’t you like to be able to read off the screen of your laptop in direct sunlight? Your mobile phone battery to last much, much longer? Or your next flat screen TV to be less expensive, much flatter, and even flexible? Well, now it is possible by an emerging technology based on the revolutionary discovery that, light emitting, fast switching diode could be made from polymers as well as semiconductors.OLED
This document discusses carbon nanotubes (CNTs), including their discovery, structure, properties, synthesis, applications, and future potential. Some key points:
- CNTs were discovered in 1991 and have a rolled-up graphene sheet structure that gives them unique mechanical and electrical properties.
- CNTs exhibit extraordinary strength and conductivity, with current-carrying capacity 1000 times higher than copper.
- Common synthesis methods are arc discharge, laser ablation, and chemical vapor deposition.
- Applications include energy storage, conductive composites, electronics, and more. Mass production is increasing and CNTs are already used in some products.
- CNTs show promise for applications across many industries
Optimal Generation of 254nm ultraviolet radiationIOSR Journals
Abstract: The science of the application of 254nm UV from mercury doped glow discharge tubes has been a major topic since Johann Ritter discovered UV via its chemical inducing reactions in 1801 and Niels Finsen’s 1860 work on UV therapy in treating rickets. In 1857 Siemens AG patented UV254nm creation via filamentary discharge, subsequently widely used for ozone production. By 1932 the Coblentz Congress had defined the three regions of the UV action spectrum. This paper presents the science of a new design for a sterilizer module fabricated from extruded, recycled aluminium. This novel design achieves better than D10 performance using six UV tubes per module driven by three electronic ballasts drawing a total current of only 1.26 amps at 240V single phase. This module delivers more than 45,000 microwatts per square centimetre of 254nm UV which sterilises one litre per second in a module with a dwell time of 1.6 seconds in a design with less than 0.5 bar pressure drop across each module. This system takes the electrical efficiency of 254 UV generation from less than 25% to more than 92% as measured by an NPL-traceable calibration against a current industry standard. Since 254nm UV generating tubes are also the basis of fluorescent lighting this new work on optimising the generation of 254nm UV also has application worldwide to improved efficiency of fluorescent tube electrical lighting, because we have shown that most of the fluorescent lamps operating today (particularly the T8 1” diameter) are running at less than 25% efficiency as opposed to the over 92% which is possible with the methods we describe. The work reported here shows that the Townsend equation for electron transport in glow discharge plasmas is not adequate since it does not address either plasma diameter or plasma drive frequency both of which fundamentally alter the electron energy transfer efficiencies to mercury atoms in the plasma.
This document summarizes an experiment investigating the ablation of dental hydroxyapatite using picosecond laser pulses. Key findings include:
- Picosecond laser pulses ablate dental enamel with no signs of thermal damage, unlike longer pulse durations.
- Spectroscopic analysis of the laser-induced plasma detected excitations of calcium and sodium, allowing distinction between healthy and carious tooth material.
- Estimates of plasma temperature and free electron density were obtained from the plasma spectra.
- Precise cavities were ablated in tooth enamel using a computer-controlled translation stage and laser system producing 30ps pulses at 1mJ energy.
This document reviews recent research on nanoscale thermal transport. It discusses how interfaces play an important role in heat transfer at the nanoscale, as the length scales are comparable to phonon mean free paths. Several experiments measuring the thermal conductance of model solid-solid interfaces are summarized. Molecular dynamics simulations are emerging as a powerful tool for studying phonon scattering and thermal conductivity at interfaces. However, fundamental questions remain regarding the definition of temperature in nonequilibrium nanoscale systems. The document goes on to discuss thermal transport in nanostructures, nanostructured materials, measurement techniques, and outlines remaining challenges in the field.
Approach To Power Harvesting With Piezoelectric MaterialIJERA Editor
Nowadays, most of the research in the energy field is to develop sources of energy for the future, With oil resources being over, tapped and eventually bound to end, it is time to find renewable Piezoelectric materials are being more and more studied as they turn out to be very unusual materials with very specific and interesting properties. In fact, these materials have the ability to produce electrical energy from mechanical energy, for example, they can convert mechanical behavior like vibrations into electricity. Recent work has shown that these materials could be used as power generators, the amount of energy produced is still very low, hence the necessity to optimize them. The objective of this work is to study the all of the piezoelectric material systems and calculated the possible power generated from it, and a special case to design and build a fully functional floor tile device that when stepped on will generate enough energy to light an LED, The system will be charge a temporary energy storage device, a capacitor bank, and then use this stored energy to power an LED.
Tor A Fjeldly and Muhammad Nawaz submitted a master's thesis on the formation of silicon nanostructures in silicon nitride thin films for use in solar cells. The goal was to develop silicon nitride anti-reflective coatings containing silicon nanoparticles and characterize the films using ellipsometry. Seven silicon nitride films with varying stoichiometry were deposited using PECVD and characterized with ellipsometry, photoluminescence, and transmission electron microscopy before and after annealing. Ellipsometry showed the films became more compact after annealing with increased refractive index. Photoluminescence was observed for samples with high ammonia flow but decreased after annealing, while samples with low ammonia flow showed little photolum
This document discusses a thesis project that aims to evaluate the radiation hardness of sensor materials for use in the proposed International Linear Collider beamline calorimeter (BeamCal). The author performs Monte Carlo simulations to estimate the shower conversion factor α, which quantifies the mean radiation fluence at a sensor per incident electron, as a function of electron energy. Analysis of the simulation data provides fluence distribution profiles that decrease radially from the center of the irradiated sensor area. The author accounts for sensor rastering across the electron beam, which provides even illumination over a 2 cm area. Observations from the simulations indicate the radiation fluence is linearly dependent on the incident electron energy.
This presentation summarizes history and recent development of perovskite solar cells. If you have any questions or comments, you can reach me at agassifeng@gmail.com
Potential enhancement of thermoelectric energy conversion in cobaltite superl...Anastasios Englezos
This document is a master's thesis submitted by Tasos Englezos investigating the potential enhancement of thermoelectric energy conversion in cobaltite oxide superlattices. The thesis aims to grow superlattices composed of alternating layers of NaxCoO3 and Ca3Co4O9 using pulsed laser deposition, as both materials show promise for thermoelectric applications but also have limitations. Characterization of the superlattices shows the structures maintain crystalline coherence while electrical and thermal properties are preserved at a good level. Further measurements of thermal conductivity are needed to determine if the superlattice approach reduces thermal conductivity and thereby improves thermoelectric efficiency in these cobaltite oxides.
Similar to Tesi Master Rupp Vitalii Volodymyrovych (20)
There is no dubt that the subject of superconducting resonant cavities is a fascinating field both physical and engineering point of view.
The application of superconductivity to the world of resonant cavities has made achievable results unimaginable otherwise.
Independently of the special field of application, superconducting resonant circuits have superior performances compared to roo-temperatire circuits.
However the greatest resource of such devices stays not in the high quality of the results already obtained, but in all potential applications and new ideas that must be still developed.
When hearing about persistent currents recirculating for several year in a superconducting loop without any appreciable decay, we realize that we are dealing with a phenomenon wich in nature is the closest we know to the perpetual motion.
The zero resistivity and the perfect diamagnetism in Mercury at 4.2 K, the discovery of superconducting materials, finally the revolution of the "liquid Nitrogen superconductivity": Nature discloses drop by drop its intimate secrets.
Nobody can exclude that the final surpreise must still come.
The document discusses plans to form an international collaboration to study future circular colliders at CERN, including a 100 TeV proton-proton collider (FCC-hh), a lepton collider (FCC-ee), and a lepton-hadron collider (FCC-he). It outlines initial parameters and opportunities for the superconducting radio frequency (RF) systems, which will need to provide up to 100 MW of continuous wave power to accelerate beams. Key areas of study for the large-scale FCC RF systems include cavity and cryomodule technology, reliability, efficiency, and operational aspects.
In questi ultimi anni i problemi energetici e ambientali hanno favorito lo sviluppo di un nuovo settore della ricerca riguardo la produzione di energia pulita sfruttando fenomeni naturali. L'attenzione dei ricercatori è stata catturata dalla possibilità di convertire l'energia solare luminosa
in energia elettrica. Questo processo di conversione, nato nella prima metà del XX secolo, permette di produrre correnti elettriche anche in piccola scala, senza la realizzazione di imponenti impianti industriali e soprattutto senza la produzione si scorie inquinanti. Sono nate così le prime celle solari
a effetto fotovoltaico.
Gli sviluppi hanno portato a diversi risultati e al giorno d'oggi l'energia fotovoltaica ha ormai fatto il suo ingresso nella vita quotidiana. Sia i favori delle industrie, sia l'interesse dei privati cittadini, contribuiscono a espandere questo tipo di ricerca, ottenendo numerosi successi nell'aumento
dell'efficienza di conversione energetica. Dal punto di vista della scienza dei materiali la prima cosa che viene in mente pensando alle celle
fotovoltaiche è il silicio. A tutti gli effetti la maggior parte delle celle sul commercio sono costituite da silicio policristallino, per le sue ottime qualità e proprietà di resa. Tuttavia esistono anche una moltitudine di altri composti, alcuni più recenti di altri, che sono ancora nell'occhio dei ricercatori, un esempio ne sono i recenti foto-materiali organici. Spesso però i costi di realizzazione sono alti per ottenere rese elevate, rendendo così proibitive le realizzazioni su impianti industriali. L'ossido rameoso (Cu2O) è stato uno dei capostipiti dei materiali utilizzati nelle celle fotovoltaiche.
Fin dal suo primo utilizzo nel 1958 esso ha presentato le caratteristiche di semiconduttore necessarie alla realizzazione di impianti fotovoltaici. Rispetto ai sui cugini più nobili, presenta delle efficienze minori, ma anche un costo decisamente più basso. Il rame infatti, da innumerevoli anni, è un elemento largamente sfruttato in tutti i campi dell'elettronica e non solo, e la realizzazione di ossidi specifici non comporta processi troppo complessi o costosi.
La ricerca nel campo dell'ossido rameoso è riuscita a migliorare le sue qualità all'interno del mondo fotovoltaico rendendo possibile la realizzazione di celle solari a costi contenuti.
Per questo motivo il Cu2O è tutt'oggi un materiale in grado di competere nel moderno panorama della ricerca solare fotovoltaica.
Il plasma è un supporto particolarmente attivo dal punto di vista chimico e fisico. In base al modo con cui viene attivato e alla potenza di lavoro, può generare temperature basse o molto elevate e viene definito rispettivamente come plasma freddo o caldo. Quest’ampio range di temperature lo rende adatto a numerose applicazioni tecnologiche: rivestimento di superficie, smaltimento rifiuti, trattamento dei gas, sintesi chimiche, lavorazioni industriali. La maggior parte di queste applicazioni del plasma non sono ancora state industrializzate, sebbene il loro sfruttamento rispetti strettamente le norme sull’inquinamento.
I plasmi caldi (specialmente quelli ad arco) sono ampiamente industrializzati, con particolare diffusione all’interno del settore aereonautico. La tecnologia dei plasmi freddi è stata sviluppata in microelettronica, ma le apparecchiature da vuoto richieste ne limitano l’applicabilità.
Al fine di evitare l’inconveniente associato al vuoto, molti laboratori hanno provato a trasferire a pressione atmosferica processi che attualmente lavorano in vuoto. Le ricerche condotte hanno portato alla scoperta di varie ed innovative sorgenti che verranno descritte in questo elaborato.
Dopo un riassunto sui differenti tipi di plasmi, saranno descritte le varie sorgenti in termini di design, condizioni di lavoro e proprietà del plasma. In seguito l’attenzione sarà spostata sulle varie applicazioni (analisi spettroscopica, trattamento dei gas e processi sui materiali).
6 GHz spun seamless Superconducting Radio Frequency (SRF) cavities are a very
useful tool for testing alternative surface treatments in the fabrication of TESLA cavity.
However, the spinning technique has also some drawbacks like contamination, surface
damage in internal part due to the collapsible mandrel line. The first important step of
the surface treatments is the mechanical polishing. For this purpose, a new, cheap, easy
and highly efficient tumbling approach based on vibration was developed.
Before this approach was conceived, a few other methods, such as Turbula,
Centrifugal Barrel Polishing (CBP), custom Zigzag tumbler and “flower brush” have
been studied and tested. But the result was not so satisfactory neither for the low erosion
rate nor for the unstableness of the system nor for the complicated polishing process. At
last, a vibration system with a simple structure, working stably was created after two
experiments.
Another important task of the thesis is to update the optical inspection system for 6
GHz cavities. 3 stepper motors motor was added to move and rotate the cavity and
realized auto focus of the miniature camera. A software was developed to achieve a full
cavity photographed by one key operation using LabVIEW.
A high-efficiency mechanical polishing system is generally judged by two aspects:
one is whether the surface property satisfies the demand after polishing; the other is
whether the erosion rate can reach and be stabilized at a high value which is comparable
or greater than the existing products. The Radio Frequency (RF) test result indicates that
the vibration system is feasible. The latest erosion rate 1 gram/hour i.e. removing 13
microns depth of inner surface materials per hour exceeds the performance of CBP,
which is widely used in other laboratories in the world.
The mechanical polishing process is elaborated and cavities that have been polished
are listed. Several influencing factors on the erosion rate, such as tumbling time, media,
signal and multi-cavities and plate direction are discussed at the end.
A preliminary design of 1.3 GHz vibration system as the future development is
provided for the next plan.
In questo lavoro di tesi verrà presentato un primo prototipo di un mini inceneritore al plasma per la pirolisi dei rifiuti medicali basato sulla tecnologia delle torce al plasma a microonde (MW) con tecnologia domestica a basso costo.
Si inizia con una breve e generale descrizione sulle problematiche dei rifiuti, della loro classificazione e delle norme che ne regolano lo smaltimento. Quindi si parlerà delle norme necessarie per l‟identificazione dei rifiuti medicali ed infine verrà riassunta la modalità di gestione dei rifiuti secondo la normativa in vigore.
Successivamente saranno descritti alcuni metodi di termodistruzione dei rifiuti ospedalieri come la combustione negli inceneritori tradizionali, e alcuni metodi alternativi, come il trattamento al plasma atmosferico, andando ad analizzare vantaggi e svantaggi di ogni tecnologia.
L‟attenzione sarà quindi focalizzata sul plasma atmosferico e sulla descrizione delle sue proprietà. Quindi saranno descritti diversi tipi di plasma atmosferico in base alle condizioni operative di alimentazione e delle loro strutture concentrando le nostre attenzioni verso le torce al plasma atmosferico basate sulle microonde.
Quindi si descriverà la realizzazione di una torcia al plasma atmosferico utilizzando i componenti a basso costo dei normali forni a microonde e con l‟obbiettivo di utilizzare questa torcia sia nel settore industriale che nella ricerca.
Tale torcia, realizzata con componenti commerciali domestici a basso costo, costituirà il cuore del prototipo di mini inceneritore che è stato progettato, realizzato, descritto e testato in laboratorio. Verrà quindi illustrata l‟efficacia di trattamento di materiale rappresentativo di rifiuti medicali come: carta, cotone idrofilo e tessuti organici biologici.
Infine verranno descritte le linee guida per gli sviluppi futuri del prototipo al fine di aumentarne l‟efficienza nel trattamento dei rifiuti, nel recupero dell‟energia derivante dalla combustione dei syn-gas e nella purificazione dei gas da agenti inquinanti.
This document provides a thermo-mechanical design of a high power neutron converter for the SPIRAL2 Facility. It includes 3 key parts:
1. A description of the neutron converter design including the graphite neutron converter, cooling system, delay window, beam collimator, and other components.
2. Analysis of material activation, radiation damage effects, and lifetime considerations for the graphite and other materials used.
3. Thermo-mechanical design calculations for the 50kW and 200kW neutron converters including temperature distributions, stresses, and deformations to validate the design meets specifications. Testing results of graphite evaporation rates, delay window performance, and ball bearing performance are also summarized.
Il forno in alto vuoto della TAV è stato costruito per l’Istituto Nazionale di Fisica Nucleare agli inizi degli anni novanta ed è installato presso i Laboratori Nazionali di Legnaro (PD) nello stabilimento Alte Energie.
E’ stato realizzato in collaborazione con la ditta milanese TAV, che ha sede a Caravaggio (MI), specializzata nella produzione di forni in vuoto. E’ stato così possibile realizzare un forno mai costruito prima e che rispondeva appieno alle esigenze richieste.
Il forno in vuoto allora in uso era un modello a caricamento orizzontale le cui pareti interne e le resistenze erano realizzate in grafite. Da allora il vecchio forno è stato congedato, mentre il nuovo impianto è entrato subito in funzione per eseguire le brasature e i trattamenti termici sulle cavità acceleratici superconduttive a quarto d’onda dell’impianto Alpi.
Da allora fino ad oggi, il nuovo forno è sempre stato operativo, e grazie ad esso è stato possibile realizzare una grande varietà di trattamenti termici e brasature, per le più svariate applicazioni e impieghi.
La tecnologia degli acceleratori di particelle è tradizionalmente un serbatoio da cui attingere per il trasferimento di conoscenze tecniche dall’ambito della ricerca di base all’industria; in questo campo i Laboratori Nazionali de Legnaro dell’Istituto Nazionale di Fisica Nucleare (LNL – INFN) vantano una lunga esperienza come ente di ricerca di alto livello sia in ambito italiano che internazionale, nello sviluppo di nuove tecniche di accelerazione e nell’applicazione di conoscenze e metodologie tipiche della scienza dei materiali al campo degli acceleratori di particelle. Il master in Trattamenti di superficie applicati a tecnologie meccaniche innovative per l’industria si inserisce in questo contesto e funge da ponte per il trasferimento del bagaglio di conoscenze maturate durante gli anni per il trattamento dei materiali delle cavità acceleratrici a realtà industriali presenti sul territorio nazionale.
Il trattamento superficiale di una cavità acceleratrice superconduttiva è un passaggio fondamentale nella sua realizzazione, in quanto predispone lo strato superficiale del risonatore stesso a sostenere le condizioni di vuoto, temperatura ed alti campi elettrici presenti durante il funzionamento nell’acceleratore; questi trattamenti presuppongono un’approfondita conoscenza della scienza dei materiali ed una robusta preparazione di tipo applicativo oltre che teorico.
Il lavoro di questa tesi prende l’avvio da due istanze fondamentali, cioè
dall’applicazione delle conoscenze fisiche, chimiche e meccaniche apprese nel corso del master e dalla tradizione nello sviluppo di nuove tecniche di accelerazione dei Laboratori Nazionali di Legnaro con il fine di realizzare e caratterizzare un nuovo tipo di strutture acceleranti basate sul concetto di cristallo fotonico o photonic band gap (PBG) applicato alle microonde.
Durante questo lavoro si sono quindi realizzati alcuni prototipi di cavità PBG risuonanti a 14 e 6 GHz, in rame ed in niobio superconduttivo, sviluppando un metodo realizzativo che permettesse di evitare il ricorso a costose saldature electron beam; le cavità così realizzate sono state trattate superficialmente adattando il protocollo di trattamento utilizzato per altre cavità costruite nei Laboratori e studiando nuove strade tecniche per la loro finitura superficiale. Infine si è proceduto ad adattare i sistemi criogenici e RF
integrandoli per caratterizzare le cavità costruite.Questo progetto si inserisce in una collaborazione fra i Laboratori Nazionali di Legnaro
e la sezione INFN di Napoli, che ha fornito il supporto teorico sulla teoria dei cristalli fotonici applicati agli acceleratori e ha contribuito al progetto delle cavità attraverso le simulazioni dei campi elettromagnetici in cavità; il gruppo di legnaro si è occupato, oltre che della costruzione, dei trattamenti di superficie e delle misure, anche della parte riguardante la superconduttività in Radiofrequenza.
L’obiettivo di questo lavoro consiste nella progettazione e costruzione di un sistema UHV multicamera per la deposizione di film sottili. La tecnica
utilizzata per crescere i ricoprimenti sottili in questo caso è l’arco catodico continuo e pulsato. Questa tecnica permette di depositare film di elevato spessore in tempi estremamente veloci. La sorgente è pressoché puntiforme in confronto allo sputtering ed i film possono essere più spessi e più puri.
L’arc vapour deposition è una tecnica di deposizione di film sottiliche cade nella grande famiglia del PVD. Essa consiste nella vaporizzazione, da un elettrodo, del materiale che si vuole depositare per mezzo di un arco. La tecnica è veloce, efficiente e relativamente poco costosa: di conseguenza è uno dei metodi più usati a livello industriale per ottenere deposizioni di film sottili con ottime proprietà meccaniche.
Negli ultimi anni si stanno effettuando numerose ricerche, sia sperimentali sia
teoriche, al fine di mettere in evidenza come questa tecnica possa essere molto utile per produrre dei film sottili in grado di aumentare le proprietà fisiche e chimiche dei rivestimenti (come ad esempio un aumento della densità, un miglioramento dell’adesione al substrato, della stechiometria dei composti e di ulteriori caratteristiche chimico-fisiche).
In particolare la letteratura russa tratta numerosi esempi di come la tecnica
dell’arco, proprio grazie all’alto grado di ionizzazione dei vapori prodotti, renda possibile la produzione di rivestimenti con determinate proprietà chimico-fisiche e strutturali per particolari condizioni di processo, non altrimenti ottenibili con altre tecniche competitive quali il magnetron sputtering o l’evaporazione tramite electron beam Come si vedrà in
seguito, infatti, l’arc vapour deposition ha il grandissimo vantaggio di controllare non solo la ionizzazione degli atomi che si vogliono depositare, attraverso una combinazione di campi elettrici e magnetici, ma anche l’energia con la quale gli ioni arrivano sul substrato.
Le sorgenti ad arco vengono inoltre utilizzate come sorgenti per LRQ EHDP che
devono produrre elevate densità di corrente.
Nel mondo industriale, infatti, questa tecnica riscuote molto interesse.Il deposito tramite arco catodico è un processo fisico sottovuoto che consente la
crescita di film duri, compatti ed aderenti su un ampio spettro di materiali al di sotto dei 300°C: Il film, estremamente sottile, ha durezze da 1000 a 3500 HV: le applicazioni industriali sono molte e variano dalla ricopertura di utensili da taglio agli tampi per le materie plastiche e lavorazioni meccaniche, da prodotti d’arredamento (maniglie, copri interruttori, pomoli, etc.) a componentistica da bagno (rubinetti, docce, tubi, etc.).
......
Fu una scoperta sensazionale quando Jun Akimitsu e colleghi annunciarono la loro scoperta nel gennaio 2001 che il diboruro di magnesio diveniva superconduttore attorno ai 40 K. L’interesse degli autori era inizialmente rivolto verso il semiconduttore CaB6 , il quale diviene ferromagnetico a seguito di trattamento leggero di doping. La loro intenzione era quella di sostituire parzialmente degli atomi di carbonio con altri di magnesio, omologo come shells elettronici ma più leggero, e gli parve conveniente utilizzare il diboruro di magnesio (ben noto sin dal 1953) per questo scopo.
L’aspetto interessante è che il magnesio diboruro è un composto molto usato nelle reazioni di sintesi del boro, dei borani, o di bururi di metalli di transizione e facilmente reperibile in qualsiasi laboratorio di chimica. E’ dunque facile immaginarsi lo stupore del mondo scientifico quando fu
comunicato che il MgB2 diviene superconduttore a temperature mai raggiunte sino ad allora da sistemi basati su semplici leghe intermetalliche non ossidate. Le fievoli speranze ed il derivante
mitigato interesse che vi era attorno ai superconduttori all’inizio della seconda metà del 1900 era dovuto soprattutto a due figure ....
In the past few decades a large amount of attention has been given to health
service’s technology. Advances in electronic components, computer technology, and images processing have contributed considerably to the expansion and improvement of the field. However, there is evidence that several other related topics still need to be explored, such as X-ray imaging in the routine mass screening for medical diagnosis.
Tumors formation is one of the most common human health problems and large
efforts have been undertaken world wide to tackle the disease. Breast cancer specifically seems to affect a large percentage of the female population. Research indicates that breast cancer treatment is most effective if the disease is diagnosed in its early stages of development. Traditionally, X-ray technologies have been used for breast screening film mammography and its success in detecting breast cancer has been reconfirmed throughout the past few decades. However, the technique has several limitations, and further improvements are required if we wish to achieve early stage diagnosis. Image formation in radiological diagnosis is the result of the complex
interdependence of many factor. Creating an ideal balance among them could improve the image to such a degree that it could be used in a clinical setting, where the minimum radiation dose would be applied to the patient. The factors which increase radiation dose and affect image quality can be grouped as: radiation quality, photon intensity, Xray detection sensitivity, and reduction of background through scattered radiation. Optimum performance is dependent on the improvement of the assessments of these phenomena. In the past, standard methods of quality control have been introduced which have lead to a partial improvement in the image evaluation techniques. Some methods, widely applied, involve the use of test objects or phantoms for the establishment of comparison parameters. However, the methods that use phantoms, are frequently not
as reliable as radiation based diagnoses of asymptomatic woman produce. In addition,the subjective nature of image interpretation by medical professionals can make the assessment process very difficult. Consequently, the currently available tools which are
used for breast clinical image formation and interpretation regularly results in an incorrect diagnosis.
In past years, the commercially introduced digital detectors for mammography
were seen as an important advancement since they provided both a higher acquisition speed and a lower associated radiation dose. However, up until this point, the quality of the produced images is comparable to the images obtained with film detectors.
....
L’adroterapia fu proposta per la prima volta da Robert R. Wilson nel 1946.
Sfruttando il modo particolare in cui gli adroni carichi depositano energia nella materia, il cosiddetto picco di Bragg, è possibile rilasciare un’elevata dose in tumori anche profondi, limitando l’irradiazione sia dei tessuti sani circostanti che del canale d’entrata. La figura della pagina seguente mostra come diversi tipi di radiazione depositano energia in acqua; in essa è ben visibile il picco degli ioni carbonio.
Gli adroni carichi rilasciano molta della loro energia alla fine del percorso; inoltre, grazie alla loro massa, hanno una traiettoria pressoché rettilinea. Queste due proprietà fondamentali permettono un trattamento conforme in cui la dose viene rilasciata nel bersaglio tumorale con un’accuratezza più elevata rispetto alla radioterapia convenzionale che si avvale di elettroni e fotoni. I tumori per i quali è indicata l’adroterapia sono quelli localizzati nella base cranica, sul fondo dell’occhio e lungo la colonna vertebrale, ma anche i tumori pediatrici, i tumori del sistema nervoso centrale, della prostata, del fegato,
dell’apparato gastroenterico e del polmone possono beneficiare di un tale trattamento.Oltre alla miglior conformazione della dose ottenibile con protoni e ioni leggeri, questi ultimi hanno il vantaggio di possedere un’elevato LET (Linear Energy Transfer ).
Questo parametro è legato alla ionizzazione indotta nei tessuti e dipende dal quadrato della carica della particella. Un’elevata densità di ionizzazione permette una doppia rottura della catena del DNA, molto più difficile da riparare di una rottura singola. Non solo, per gli adroni il LET è più elevato nel picco di Bragg che nel canale di entrata. Tuttavia ioni con Z troppo elevato possono causare gravi danni sia nel canale d’entrata che nella coda (cioè oltre il picco di Bragg). La carica Z dello ione va dunque determinata con particolare cura: allo stato attuale delle conoscenze la scelta migliore è lo ione C6+ caratterizzato da una efficacia biologica relativa (RBE) che è circa tre volte quella dei protoni nella regione del picco di Bragg mentre rimane pressoché la stessa nel canale d’entrata. Gli ioni C6+ sembrano quindi essere i più adatti per il trattamento di tumori radioresistenti.1 2
L’acceleratore del CNAO – Centro Nazionale di Adroterapia Oncologico è un
acceleratore normalconduttivo costituito da due sorgenti ECR per la produzione di ioni carbonio C4+ e H3+. Una linea di trasporto a bassa energia LEBT, un acceleratore lineare LINAC costituito da un RFQ ed una struttura IH – DTL che accelera il fascio da 8 keV/u a 7 MeV/u. Il fascio incontra quindi uno stripper foil di Carbonio passando dallo stato di carica tetravalente a quello esavalente per poi essere accelerato dalla cavità RF del sincrotrone.
Le cavità acceleratici del Linac sono strutture normalconduttive in acciaio ramato per via elettrochimica. Risulta di fondamen
Questo lavoro di tesi si propone di individuare, studiare e realizzare un dispositivo da applicare alle sorgenti magnetron-sputtering per aumentare la velocità delle deposizioni di film sottili. Le prove di deposizione sono state fatte utilizzando il niobio inquanto il dispositivo studiato potrebbe venire applicato alla deposizione di questo metallo superconduttore all’interno di cavità acceleratrici in radiofrequenza per acceleratori di particelle. Il problema che ci si è proposti di risolvere è quello di aumentare l’efficienza di ionizzazione del plasma da parte degli elettroni prodotti da una scarica elettrica in vuoto del tipo glow discharge. In una sorgente a diodo gli elettroni vengono persi perché assorbiti dall’anodo. In un magnetron gli stessi elettroni vengono fatti spiralizzare attorno alle linee di campo magnetico e compiendo un percorso più lungo per arrivare all’anodo effettuano un numero maggiore di collisioni ionizzanti.
Varie scuole di pensiero puntano ad aumentare l’efficienza di ionizzazione utilizzando differenti soluzioni (per esempio coupling del plasma induttivo con una sorgente a mircoonde, ECR), nel nostro caso sono state sviluppate delle sorgenti “extra” di elettroni chiamate Hollow Cathode da affiancare ai magnetron in modo da aumentare il numero di elettroni utili per la ionizzazione.
Recentemente la realizzazione di sorgenti magnetron-sputtering compatte, semplici e poco costose ha esteso l’utilizzo delle tecniche di deposizione di film sottili anche al settore low-tech come per esempio quello dei ricoprimenti decorativi oppure protettivi per il packaging nell’industria alimentare. Questo lavoro di tesi quindi, proponendosi di velocizzare la produzione di film sottili e di migliorarne la qualità, si inserisce in un contesto industriale di grande attualità
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
Microbial interaction
Microorganisms interacts with each other and can be physically associated with another organisms in a variety of ways.
One organism can be located on the surface of another organism as an ectobiont or located within another organism as endobiont.
Microbial interaction may be positive such as mutualism, proto-cooperation, commensalism or may be negative such as parasitism, predation or competition
Types of microbial interaction
Positive interaction: mutualism, proto-cooperation, commensalism
Negative interaction: Ammensalism (antagonism), parasitism, predation, competition
I. Mutualism:
It is defined as the relationship in which each organism in interaction gets benefits from association. It is an obligatory relationship in which mutualist and host are metabolically dependent on each other.
Mutualistic relationship is very specific where one member of association cannot be replaced by another species.
Mutualism require close physical contact between interacting organisms.
Relationship of mutualism allows organisms to exist in habitat that could not occupied by either species alone.
Mutualistic relationship between organisms allows them to act as a single organism.
Examples of mutualism:
i. Lichens:
Lichens are excellent example of mutualism.
They are the association of specific fungi and certain genus of algae. In lichen, fungal partner is called mycobiont and algal partner is called
II. Syntrophism:
It is an association in which the growth of one organism either depends on or improved by the substrate provided by another organism.
In syntrophism both organism in association gets benefits.
Compound A
Utilized by population 1
Compound B
Utilized by population 2
Compound C
utilized by both Population 1+2
Products
In this theoretical example of syntrophism, population 1 is able to utilize and metabolize compound A, forming compound B but cannot metabolize beyond compound B without co-operation of population 2. Population 2is unable to utilize compound A but it can metabolize compound B forming compound C. Then both population 1 and 2 are able to carry out metabolic reaction which leads to formation of end product that neither population could produce alone.
Examples of syntrophism:
i. Methanogenic ecosystem in sludge digester
Methane produced by methanogenic bacteria depends upon interspecies hydrogen transfer by other fermentative bacteria.
Anaerobic fermentative bacteria generate CO2 and H2 utilizing carbohydrates which is then utilized by methanogenic bacteria (Methanobacter) to produce methane.
ii. Lactobacillus arobinosus and Enterococcus faecalis:
In the minimal media, Lactobacillus arobinosus and Enterococcus faecalis are able to grow together but not alone.
The synergistic relationship between E. faecalis and L. arobinosus occurs in which E. faecalis require folic acid
The cost of acquiring information by natural selectionCarl Bergstrom
This is a short talk that I gave at the Banff International Research Station workshop on Modeling and Theory in Population Biology. The idea is to try to understand how the burden of natural selection relates to the amount of information that selection puts into the genome.
It's based on the first part of this research paper:
The cost of information acquisition by natural selection
Ryan Seamus McGee, Olivia Kosterlitz, Artem Kaznatcheev, Benjamin Kerr, Carl T. Bergstrom
bioRxiv 2022.07.02.498577; doi: https://doi.org/10.1101/2022.07.02.498577
ESA/ACT Science Coffee: Diego Blas - Gravitational wave detection with orbita...Advanced-Concepts-Team
Presentation in the Science Coffee of the Advanced Concepts Team of the European Space Agency on the 07.06.2024.
Speaker: Diego Blas (IFAE/ICREA)
Title: Gravitational wave detection with orbital motion of Moon and artificial
Abstract:
In this talk I will describe some recent ideas to find gravitational waves from supermassive black holes or of primordial origin by studying their secular effect on the orbital motion of the Moon or satellites that are laser ranged.
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...PsychoTech Services
A proprietary approach developed by bringing together the best of learning theories from Psychology, design principles from the world of visualization, and pedagogical methods from over a decade of training experience, that enables you to: Learn better, faster!
SDSS1335+0728: The awakening of a ∼ 106M⊙ black hole⋆Sérgio Sacani
Context. The early-type galaxy SDSS J133519.91+072807.4 (hereafter SDSS1335+0728), which had exhibited no prior optical variations during the preceding two decades, began showing significant nuclear variability in the Zwicky Transient Facility (ZTF) alert stream from December 2019 (as ZTF19acnskyy). This variability behaviour, coupled with the host-galaxy properties, suggests that SDSS1335+0728 hosts a ∼ 106M⊙ black hole (BH) that is currently in the process of ‘turning on’. Aims. We present a multi-wavelength photometric analysis and spectroscopic follow-up performed with the aim of better understanding the origin of the nuclear variations detected in SDSS1335+0728. Methods. We used archival photometry (from WISE, 2MASS, SDSS, GALEX, eROSITA) and spectroscopic data (from SDSS and LAMOST) to study the state of SDSS1335+0728 prior to December 2019, and new observations from Swift, SOAR/Goodman, VLT/X-shooter, and Keck/LRIS taken after its turn-on to characterise its current state. We analysed the variability of SDSS1335+0728 in the X-ray/UV/optical/mid-infrared range, modelled its spectral energy distribution prior to and after December 2019, and studied the evolution of its UV/optical spectra. Results. From our multi-wavelength photometric analysis, we find that: (a) since 2021, the UV flux (from Swift/UVOT observations) is four times brighter than the flux reported by GALEX in 2004; (b) since June 2022, the mid-infrared flux has risen more than two times, and the W1−W2 WISE colour has become redder; and (c) since February 2024, the source has begun showing X-ray emission. From our spectroscopic follow-up, we see that (i) the narrow emission line ratios are now consistent with a more energetic ionising continuum; (ii) broad emission lines are not detected; and (iii) the [OIII] line increased its flux ∼ 3.6 years after the first ZTF alert, which implies a relatively compact narrow-line-emitting region. Conclusions. We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 106M⊙ AGN that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGNobserved in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour. Key words. galaxies: active– accretion, accretion discs– galaxies: individual: SDSS J133519.91+072807.4
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
TOPIC OF DISCUSSION: CENTRIFUGATION SLIDESHARE.pptxshubhijain836
Centrifugation is a powerful technique used in laboratories to separate components of a heterogeneous mixture based on their density. This process utilizes centrifugal force to rapidly spin samples, causing denser particles to migrate outward more quickly than lighter ones. As a result, distinct layers form within the sample tube, allowing for easy isolation and purification of target substances.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
1. UNIVERSITÀ DEGLI
STUDI DI PADOVA
Facoltà di Scienze MM.NN.FF.
Facoltà di Ingegneria
ISTITUTO NAZIONALE DI
FISICA NUCLEARE
Laboratori Nazionali di
Legnaro
in collaboration with Confindustria Veneto
MASTER THESIS
in
“Surface Treatments for Industrial Applications”
Electropolishing of Niobium 6 GHz rf cavities in
fluorine-free electrolyte
Supervisor: Prof. V. Palmieri
Assistant supervisor : Dr. V. Rampazzo
Student:
Dott. Rupp Vitalii
Volodymyrovych
Matr. №: 934605
Academic Year 2008-09
6. 6 ACRONYM
Acronym
EP – Electropolishing
BCP – Buffered Chemical Polishing
IL – ionic liquid
ChCl – Choline Chloride
SA – Sulfamic acid
PS - Ammonium persulfate
SRF – Superconducting Radio Frequency
BSC – microscopic theory of superconductivity, proposed by Bardeen, Cooper, and
Schrieffer in 1957
WE – working electrode
CE – counter electrode
RE – reference electrode
7. Abstract 7
Abstract
Electropolishing is one of the oldest electrochemical techniques which is widely
adapted in industry. Since many years electropolishing has been growing and from day to day
it fills more and more niches in different fields of science and technology. Among possible
Surface Treatments, electropolishing occupies a key role, because it is the cleanest way for
removing hundreds of microns of material.
Most galvanic processes start their life from water solutions. Electropolishing is not an
exception, even now Nb electropolishing based on water solution with sulfuric and
hydrofluoric acids is the most used. Literature results with this standard mixture are excellent,
however the EP of thousands of cavities could become an industrial nightmare from the point
of view of security at work. HF is not like other highly corrosive acids: if, by accident, it gets
in contact with skin, pain is not felt, but F- ions begin to pass through, searching for the bone
calcium.
Since many years world’s science has been interested in ionic liquids and it is not for
nothing. A green chemistry based on ionic liquids has come to the fore, and at INFN-LNL
laboratories was done the first Niobium electropolishing by a harmless mixture of Choline
Chloride and urea heated around 150°C.
In my work I will try to study influence of adding to the mixture some regulators.
While it has already been showed the possibility of Nb dissolving with electropolishing effect,
I will try to find recipe for technological Nb electropolishing. My second goal is to put ready
recipe to application on 6 GHz cavities.
8. 8 INTRODUCTION
Introduction
0.1 Superconducting cavities
A superconducting cavity is the device used to provide energy to the particles that are
crucial to an accelerator. Most commonly used are radio frequency (rf) cavities, an example of
which is shown in Figure 0.1.
Figure 0.1: The first Niobium seamless 9-cell cavity ever fabricated [1]
In the past, copper cavities were used for acceleration (e.g., at SLAC). However,
superconducting niobium technology has proven itself over the last 20 years as a promising
alternative, being used in machines such as HERA (Hamburg, Germany) and TJNAF (Newport
News, VA). Continuous wave (cw) accelerating gradients of 10 MV/m have been achieved,
exceeding levels that are possible with copper cavities. Many of the present and future projects
(among them TESLA, LEP-II, the KEK B-factory, and the LHC) are relying on superconducting
cavities to achieve their design goals. Thus, superconductors will play a pioneering role at both
the energy frontier and the high current frontier.
Extensive research has therefore been performed to understand the performance
limitations of superconducting cavities and to improve upon the achieved accelerating gradients.
0.1.1 Advantages of superconducting cavities
Although not completely loss free above T = 0 K, as in the dc case, superconducting
cavities dissipate orders of magnitude less power than normal conducting cavities. Niobium
cavities, like those installed at TJNAF, routinely achieve quality (Q0) factors 105 to 106 times
that of copper cavities. The dramatically reduced resistivity translates into a number of very
important advantages.
9. Superconducting cavities 9
0.1.2 Radio-frequency fields in cavities
The rf field in cavities is derived from the eigenvalue equation
⎛ 2
⎞⎛ ⎞
⎜∇ 2
∂ − = ⎝ ∂ ⎟⎜ ⎟ ⎠⎝ ⎠
1 0
2 2
E
c t H
(0.1)
which is obtained by combining Maxwell's equations [2; 3]. It is subject to the boundary
conditions
nˆ×Ε = 0 (0.2)
and
nˆ×H = 0 (0.3)
at the cavity walls. Here ݊ො
is the unit normal to the rf surface, c is the speed of light and E and H
.
are the electric and magnetic field respectively. In cylindrically symmetric cavities, such as the
pillbox shape, the discrete mode spectrum given by equation (0.1) splits into two groups,
transverse magnetic (TM) modes and transverse electric (TE) modes. For TM modes the
magnetic field is transverse to the cavity symmetry axis where as for TE modes it is the electric
one to be transverse. For accelerating cavities, therefore, only TM modes are useful.
The typical shape of speed of light cavities [3] is shown in Figure 0.2.
Figure 0.2: Schematic of a generic speed-of-light cavity. The electric field is strongest near the
symmetric axis, while the magnetic field is concentrated in the equator region.
10. 10 INTRODUCTION
0.1.3 The accelerating field
The accelerating voltage (Vacc) of a cavity is determined by considering the motion of a
charged particle along the beam axis. For a charge q, by definition,
1 (maximum energy gain possible during transit) acc V
= ⋅ (0.4)
q
We used speed-of-light structures in our tests, and the accelerating voltage is therefore
given by
d fw z
( ) 0
Vacc Ez 0,
z e c dz
ρ = = ∫=
0
z
(0.5)
where d is the length of the cavity and ω0 is the eigenfrequency of the cavity mode under
consideration. Frequently, one quotes the accelerating field Eacc rather than Vacc. The two are
related by
Vacc Eacc d
= (0.6)
0.1.4 Peak surface fields
When considering the practical limitations of superconducting cavities, two fields are of
particular importance: the peak electric surface field (Epk) and the peak magnetic surface field
(Hpk). These fields determine the maximum achievable accelerating gradient in cavities. The
surface electric field peaks near the irises, and the surface magnetic field is at its maximum near
the equator.
To maximize the potential cavity performance, it is important that the ratios of Epk = Eacc
and Hpk = Eacc be minimized.
0.1.5 RF power dissipation and cavity quality
To support the electromagnetic fields in the cavity, currents flow in the cavity walls at the
surface. If the walls are resistive, the currents dissipate power. The resistivity of the walls is
characterized by the material dependent surface resistance Rs which is defined via the power Pd
dissipated per unit area:
1 2
2
dP
da
d R H s
= (0.7)
11. Superconducting cavities 11
In this case, H is the local surface magnetic field.
Directly related to the power dissipation is an important figure of merit called the cavity
quality (Q0). It is defined as
w U
0
Q
= (0.8)
0 P
d
U being the energy stored in the cavity. The Q0 is just 2π times the number of rf cycles it
takes to dissipate an energy equal to that stored in the cavity.
For all cavity modes, the time averaged energy in the electric field equals that in the
magnetic field, so the total energy in the cavity is given by
1 1
2 V 2 V
U = μ 2 0 ∫ H dv = ε 2
0
∫ E dv (0.9)
where the integral is taken over the volume of the cavity. The dissipated power becomes
1 2
2 S
d s P = ∫ R H ds (0.10)
where the integration is taken over the interior cavity surface. (By keeping Rs in the
integral we have allowed for a variation of the surface resistance with position.) Thus one finds
for Q0:
2
w μ
Hdv
0 0
V
0 2
s
s
Q
R H ds
=
∫
∫
(0.11)
The Q0 is frequently written as
Q G
0
= (0.12)
s
R
where
2
w RH dv
0 0
s
2
V
s
G
H ds
μ
=
∫
∫
(0.13)
is known as the geometry constant, and
12. 12 INTRODUCTION
2
R H ds
2
s
s
s
s
R
H ds
=
∫
∫
(0.14)
is the mean surface resistance (weighted by |H|2).
Although superconductors do not exhibit any dc resistivity, there are small losses for rf
currents.
0.2 Cavities configurations
Superconducting cavities are (or were) in operation in many storage rings (HERA [4],
LEP [5], Tristan [6], KEK [7], CESR [8]) or linacs (Jefferson Lab [9], TFF-FEL [10]). At
present the superconducting proton linac for the SNS spallation source is under construction
[11]. In total more than 1000 meter of superconducting cavities have been operated and delivered
about 5 GeV of accelerating voltage [12]. TESLA [13] is a proposal for a superconducting linear
collider using more than 20000 Niobium cavities. Many other projects using superconducting
cavities are under discussion (light sources, muon colliders,…). Most existing cavities are made
from Niobium sheet metal.
The fabrication of Niobium cavities has become a mature technology. Several companies
are qualified as competent producers. The fabrication process of resonators for electron
acceleration (relative velocity beta = v/c =1) is described with special reference to the TESLA
design (Figure 0.3), especially considering mass production aspects. The design for medium beta
application as for protons looks very similar. The shape of resonators for low beta application
(like heavy ions) is different but the fabrication principles are the same.
Two classes of considerations govern the structure design. The particular accelerator
application forms one class, and superconducting surface properties the other. Designing a
superconducting cavity is a strong interplay between these two classes. Typical accelerator
driving aspects are the desired voltage, the duty factor of accelerator operation, beam current or
beam power. Other properties of the beam, such as the bunch length, also play a role in cavity
design. Typical superconducting properties are the microwave surface resistance and the
tolerable surface electric and magnetic fields. These properties, set the operating field levels and
the power requirements, both RF power as well as AC operating power, together with the
warning temperature.
13. Accelerator requirements and example systems 13
Figure 0.3: Modified TESLA 9-cell resonator (with LHe tank at lower picture) as example for a β
= 1 structure for acceleration of electrons (courtesy of Accel Instruments GmbH).
Figure 0.4 shows a variety of superconducting accelerating cavities, ranging in frequency
from 200 MHz to 3000 MHz and ranging in number of cells from one to nine. Most are cavities
fabricated from pure sheet niobium. All the cavities of Figure 0.4 are intended for accelerating
particles moving at nearly the velocity of light, i.e. v/c = β ≈ 1. Accordingly, the period of a long
structure (or the accelerating gap) is λ/2, where λ is the RF wavelength. Particles moving at v ≈ c
will cross the gap in exactly a half RF period to receive the maximum acceleration.
Figure 0.4: A spectrum of superconducting cavities.
0.3 Accelerator requirements and example systems
Superconducting cavities have found successful application in a variety of accelerators
spanning a wide range of accelerator requirements. High current storage rings for synchrotron
light sources or for high luminosity, high energy physics with energies of a few GeV call for
acceleration voltages of less than 10 MV, and carry high CW beam currents up to one amp.
Figure 0.5 [14] shows the accelerating structure based on a 500 MHz, single cell cavity that
evolved for the Cornell storage ring CESR/CHESS. The cavity was fabricated from pure sheet
niobium. Four such systems provide the needed voltage of 7 MV and beam power of more than
14. 14 INTRODUCTION
one MW. Similar systems are under construction to upgrade the beam current of the existing
Taiwan Light Source (SRRC), and for the new Canadian Light Source (CLS). The accelerating
gradient choice for all these cases is 7 MV/m or less.
Figure 0.5 (Left) 3D-CAD drawing of the CESR superconducting cavity cryomodule . (Right) 500
MHz Nb cavity.
Near the energy frontier, LEP-II at CERN called for an accelerating voltage for nearly 3
GV to upgrade the beam energy from 50 to 100 GeV per beam, with a beam current of a few
mA. With a frequency choice of 350 MHz, dominated by higher order mode (HOM) power loss
and beam stability considerations, a 4-cell structure emerged [15]. To build 300 such units there
was considerable savings in material cost by fabricating the cavity out of copper and coating it
with niobium by sputtering. The LEP-II cavities (Figure 0.6) operated successfully at an average
gradient of 6 MV/m.
Figure 0.6: A 4-cell, 350 MHz Nb-Cu cavity for LEP-II
A one GeV CW linac forms the basis for CEBAF, a 5-pass recirculating accelerator
providing 5-6 GeV CW beam for nuclear physics [16]. The total circulating beam current is a
few mA. Developed at Cornell, the 5-cell, 1500 MHz cavities (Figure 0.7) are also fabricated
from solid sheet niobium. CEBAF cavities operate at an average accelerating field of 6 MV/m.
15. Accelerator requirements and example systems 15
Figure 0.7: A pair of 5-cell Nb cavities developed at Cornell for CEBAF
All the above accelerators run CW at 100% duty factor. The first pulsed superconducting
linac will be for the Spallation Neutron Source (SNS) at Oak Ridge. 6-cell niobium cavities at
804 MHz will accelerate a high intensity (≈10 mA) proton beam from 200 MeV to 1000 MeV.
Figure 0.8 shows the medium β =0.64 cavity that resembles a β = 1 cavity that is squashed [17].
The duty factor for SNS is 6% and the RF pulse length is one ms. With recent improvement in
cavity gradients the anticipated gradient is near 15 MV/m. Besides spallation neutron sources
SNS technology could become suitable for high intensity proton linacs for various applications,
such as transmutation of nuclear waste or generation of intense muon beams.
Figure 0.8: b = 0.6, 6-cell cavity for SNS, frequency 804 MHz
The dream machine for the future will be a 500 GeV energy frontier linac colliding
electrons and positrons, upgradable to one TeV. As we will see, refrigerator power
considerations drive the duty factor of operation to one percent. The average beam current is
about 10 μA. A 9-cell niobium cavity design (Figure 0.9) has emerged from the TESLA
collaboration [18]. With gradients improving steadily over the last decade, the choice of 25
MV/m will lead to 20 km of cavities for the 500 GeV machine. TESLA technology is likely to
become the basis for the free electron lasers providing high brightness beams with wavelengths
from the infra-red to ultraviolet and ultimately x-rays.
16. 16 INTRODUCTION
Figure 0.9: 1300 MHz 9-cell cavity for TESLA
For the far future, acceleration of muons will also benefit from superconducting cavities
[19]. A neutrino factory providing an intense neutrino beam from decaying muons may be the
first step towards a muon collider that will penetrate the multi-TeV energy scale. At low energies
(< a few GeV), where the muons have a large energy spread, the RF frequency has to be very
low, e.g 200 MHz, leading to gigantic structures. Once again economics will favor thin film Nb-
Cu cavities over sheet Nb cavities. For comparison, a single cell Nb-Cu cavity at 200 MHz
(Figure 0.4) dominates the size of superconducting cavities for the variety of accelerator
applications discussed.
0.4 6 GHz cavities
People study the effectiveness of innovative surface treatments, new thin film deposition
techniques, new suprconducting materials for rf applications using samples. Their rf
characterization is an useful diagnostic tool to accurately investigate local properties. However a
common limitation of the systems used often consists in the difficulty of scaling the measured
results to the real resonator [20; 21].
0.4.1 Application
The rf performance testing of a sample and its extrapolation to the frequency of a cavity
is and will always remain an indirect way of measuring superconducting rf properties. Obviously
the most direct way to test rf properties would be the use of cavities but 1.5 GHz resonant
structures would be too onerous both for the material cost and the cryogenic expense. The idea
was to build micro cavities completely equal in shape to the real scale model.
Using 6GHz cavities is possible to perform a high numbers of rf tests reducing research
budget. RF measured samples will never be comparable to a real large cavity. It is always an
indirect measurement. 6 GHz cavities are at the same time easy to handle like a sample but they
are “real” cavities.
They are made from larger cavities fabrication remaining material using spinning
technology, they don’t need welding (even for flanges) and finally they can be directly measured
17. 6 GHz cavities 17
inside a liquid helium dewar. While 1,3 – 1,5 GHz cavities need no less than 1 week time
preparation for the RF test. With 6 GHz cavities it is possible to perform more than one rf test
per day.
With a tool like this it is possible to study traditional and innovative surface treatments
and to perform rf tests on a large amount of cavities with a research budget much lower than the
one necessary to treat and tests real cavities. It is also possible to study new thin film
superconducting materials grown for example by sputtering or thermal diffusion.
0.4.2 Geometry
Figure 0.10: The 6 GHz cavity geometry.
6 GHz cavities are 97 mm long and have a 45 mm diameter cell, an electrical length of 25
mm and the same shape as a large resonator. They have two large flat flanges at the ends. For
each of them the available surface to ensure the vacuum sealing is equal to 7 cm2.
0.4.3 Fabrication technique
6 GHz cavities are made using the spinning technology (Figure 0.11). it can be used, also
for real resonators.
High beta superconducting cavities are commonly manufactured by spinning two half-cells,
which are then electron-beam welded together from the inside. Welding is a complicated
18. 18 INTRODUCTION
and costly operation that places severe limitations on the fabrication of high frequency cavities
due to the narrow size of the bore.
At the National Institute of Nuclear Physics in Legnaro (LNL-INFN) [22] the well-known
spinning technique has been adapted to form a fully seamless resonator without electron
beam welding. In this way, starting from a disk or a seamless tube, it is possible to build
seamless cavities with no intermediate annealing, more rapidly, simply, and with a uniform
thickness. Both 1,5 GHz niobium and copper cavities can be easily manufactured with high
reproducibility and significant savings in manufacture costs.
Figure 0.11: Snapshots of a 9cell cavity during the spin moulding.
The 6 GHz cavities produced by spinning are obtained using larger cavities fabrication
remaining material (scraps) as shown in Figure 0.12.
19. 6 GH
Hz cavities
ure 0.12: On
Figu
0.4.4 S
6 GHz c
igure 0.10,
these reason
ties (Figure
in Fi
For t
cavit
n the right a
Summary
avities don'
finally thei
ns it is possi
0.13) with
F
scrap, of a
large Nb
nators from
reson
't need any k
ir productio
ible to cont
a low resea
cavity, from
the 4 corne
kind of elec
on requires
trol the cost
arch budget.
igure 0.13:
m which are
ers.
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“A great ar
e obtained 4
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ction and to
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ven for flan
me, half a d
realize a la
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small 6 GH
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20. 20 INTRODUCTION
Using rf characterization of superconducting samples would be an useful diagnostic way
to accurately investigate local properties of a bulk superconductor, of the grown superconducting
films and given surface treatments on them.
However, common limitations of systems used for RF characterization of
superconducting samples, often consist in the difficulty of samples preparation and scaling up
the measured results to the real resonator.
Obviously the most direct way to test RF properties of a superconductor would be the use
real size cavities, but 1.5 GHz resonant structures would be too onerous both for costs and time
consuming.
9 For chemical surface treatments it is necessary to use a huge quantity of acids: they
are expensive and dangerous.
9 Experimental infrastructures are big and pricy, in particular the cryogenic apparatus.
It is complex and it has to be filled with more than 400 litres of liquid helium for a
single RF test.
9 Moreover the RF testing procedure takes a long time. It includes the cavity pumping,
bake out, cooling at 4,2 K and cooling at 1,8 K. Generally to perform only one RF
test one week is not enough!
Therefore the idea to build micro-cavities completely equal in shape to the real scale
model brings a lot of opportunities. In Figure 0.14 is illustrated accordance of rf superconducting
properties of samples and superconducting 6 GHz cavities to reality. Any sample extrapolation
will be far from the accuracy obtainable with a real superconducting resonator like a 6 GHz
cavity.
21. 6 GHz cavities 21
Figure 0.14: A visual of accordance to reality of RF properties of superconducting samples and
superconducting 6 GHz cavities. Any sample extrapolation will be far from the accuracy
obtainable with a real superconducting resonator like a 6 GHz cavity.
22. 22 ELECTROPOLISHING FUNDAMENTALS
1 Electropolishing fundamentals
Electropolishing (EP) is a process in which a metallic surface is made smoothed by
anodic dissolution [23]. The discovery of EP goes back to the beginning of the 20th century [24;
25]. Jacquet was the first to investigate EP systematically and received a patent in the 1930s
[26]. Today, EP is a well-developed method divided into various research branches such as the
practical applications including medical device fabrication and mechanical deformation-free
preparation of metals for imaging in transmission electron microscopy (TEM), and the
fundamental researches including the mechanism investigation and quantitative simulation.
1.1 Macrosmoothing and microsmoothing
In the literature, EP regimes are commonly referred to as anodic leveling and brightening,
or macrosmoothing and microsmoothing [23; 27]. Meanings of macrosmoothing can be the
elimination of roughness with heights over 1 μm, and microsmoothing to the elimination of
roughness under 1 μm. However, the distinction of macrosmoothing and microsmoothing based
on roughness is just a simplification. The value of 1 μm is not a criterion. There is no simple
correlation between profile heights measured by mechanical means such as profilometry and that
corresponding to optical brightness testing [28].
It is thought that different mechanisms are suitable for macrosmoothing and
microsmoothing [23; 29; 30; 31; 32]. Macrosmoothing results from the higher current leading to
the higher local dissolution rate on peaks. This is under an ohmic control (or voltage control).
Theoretical prediction of local macrosmoothing rate based on the Nernst diffusion layer model is
in good agreement with experimental results.
Microsmoothing on the other hand results from the suppression of the influence of
surface defects and crystallographic orientation on the dissolution process [23]. Microsmoothing
is the final finish of EP. The mechanism of microsmoothing is rather complex [26; 33; 34]. It is
accepted that microsmoothing occurs under mass transport limiting current with the presence of
an anodic film on the metal surface [35; 36; 37; 38; 39]. About the nature of anodic film, some
researchers favor a thin compact salt film consisting of an oxide contaminated with significant
amounts of anions from solution, and others favor a highly viscous and anhydrous film. Only the
metal ion is mobile in the anodic salt film. One performing EP usually wants to achieve both
macrosmoothing and microsmoothing, but in practice it is possible to only achieve
macrosmoothing without microsmoothing and vice versa [40].
23. Nernst diffusion layer 23
1.2 Nernst diffusion layer
Figure 1.1 is a schematic diagram of the Nernst diffusion layer model under ideal
conditions [23]. The macrosmoothing rate is equal to the difference in dissolution rate between
peaks and valleys of a rough surface. The difference in dissolution is determined by the local
current distribution along the surface profile [23]. An arbitrary two-dimension surface profile is
treated as a Fourier sine series [41]. The corresponding parameters are: the initial profile height
ε0, the wavelength λ, and the diffusion layer thickness δ. When δ >> ε0, the interface between the
diffusion layer and the bulk electrolyte will be flat. The difference in distance from the metal
surface to the interface – for example in Figure 1.1, AB < CD – results in a difference in
resistance, that is, RAB < RCD. The current density at point A (peak) is larger than that at point C
(valley), resulting in the reduction of peak heights typically > 1 μm. If ε0 >> δ, the diffusion layer
will follow the surface profile in a perfect way as shown by the broken line in Figure 1.1. In this
case, there is no difference in resistance along the surface, in Figure 1.1 for example, AB’ = CD’
=> RAB’ = RCD’. The current density is uniform, i.e. no profile flattening. The wavelength λ also
contributes to the macrosmoothing rate. Wagner and McGeough conclude that the larger the
ratio of λ/ε0, the smaller the smoothing rate [41; 42].
Figure 1.1: Schematic diagram of the Nernst diffusion layer model [23].
24. 24 ELECTROPOLISHING FUNDAMENTALS
1.3 Mass transport mechanism
Mass transport is the only condition that leads to microsmoothing. Figure 1.2 summarizes
the three possible mass transport mechanisms proposed in the literature [23]. Mechanism 1 – salt
precipitation - considers rate limiting diffusion of cations (M+) of the dissolving metal from the
anode to the electrolyte. During EP within the limiting current region a salt film presents on the
anodic surface where the concentration of M+ in the salt film is equal to the saturation
concentration. The anions (A-) from the electrolyte also accumulate within the anodic film to
maintain the electro-neutrality. Mechanism 2 – acceptor anion limited – is limited by the
transport of acceptor anions (A-) to the metal surface. Mechanism 3 – hydrogen limited –
considers the diffusion of water from the electrolyte to the anode as the rate limiting process.
Regardless of the mechanisms, mass transport of the dissolved metal ions is the limiting factor
responsible for the shift from surface etching to microsmoothing. In all these EP cases, the
estimation of the surface concentration of the dissolving metal ions at the limiting current yields
values in reasonable agreement with the saturation concentration.
Figure 1.2: Schematic diagram of three mass transport mechanisms involving (1) salt film, (2)
acceptor, and (3) water as transport species. Csat is the saturation concentration and δ is the
thickness of Nernst diffusion layer [35].
25. Physical properties 25
2 Niobium properties
2.1 Physical properties
Niobium is a transition metal of V group and fifth period. It is a chemical element that
has the symbol Nb and atomic number 41. A soft, gray, ductile transition metal, Niobium is
found in pyrochlore and columbite. It was first discovered in the latter mineral and so was
initially named columbium; now that mineral is also called "niobite". Niobium is also used in
special steel alloys as well as in welding, nuclear industries, electronics, optics and jewelry. In
the family of superconducting element it has the highest critical temperature and its properties
are collected in Table 2.1.
Atomic number 41
Atomic weight 92,9 g/mol
Atomic radius 2.08
Density 8570 kg m−3
Crystalline lattice b.c.c.
Space group Im3m
a 3,3033
Electrical resistivity (300K) 14.9 μΩ·cm
Thermal conductivity (300K) 53.7 W m-1K-1
Debye Temperature 275K
Melting Point 2741K
Critical temperature 9.26K
Density 8570 kg m−3
Table 2.1: List of the niobium properties
2.2 Superconductive properties
Of the known practically usable superconductors, Nb has the highest bulk μ0Hc1 = 170
mT and, hence, is used for RF cavity applications. An overview of relevant material properties
for Nb is presented in Table 2.2. The parameters are given at T = 0 K. Since Nb cavities will be
mainly operated at about 2 K and derivatives for T → 0 are zero, the zero temperature values can
be expected to be sufficiently accurate. Nb cavities can exhibit a drop in Q0 towards higher Eacc.
This so-called Q-drop is not fully understood, but appears to be related to Nb-oxides at the cavity
surface. For bulk cavities, the Q-drop can be significantly reduced by baking the cavity at about
26. 26 NIOBIUM PROPERTIES
500°C, which presumably redistributes the oxygen. For thin Nb film on Cu cavities the Q-drop
cannot, for now, be prevented. The present state-of-the-art bulk Nb cavities exhibit, at T = 2 K, a
Q0 above 1010 until an Eacc of about 50 MV/m, at which point the cavities quench. Note that Nb
cavities have to be operated in superfluid Helium (i.e. below 2.2 K) at frequencies above about 1
GHz, since at higher temperatures the BCS losses become too excessive.
An Eacc ≅50 MV/m corresponds closely to the magnetic field limit for Nb. Differences
between achieving Hc1, Hsh or H are virtually indistinguishable for Nb. Nevertheless, achieving
the magnetic field limitation for Nb cavities means that Nb is exhausted for a further increase in
the accelerating voltage.
Property Nb
Tc [K] 9.2
μ0Hc1 [T] 0.17
μ0Hc(0) [T] 0.2
μ0Hc1(0) [T] 0.4
ξGL(0) [nm]1 29
λeff (0) [nm]2 41
k·(0)3 1.4
Δ(0) [meV]4 1.4
ρn
[μΩcm] < 100(VERIFY!)
Table 2.2: Characteristic superconductive parameters of Nb [43]
2.3 Chemical properties
Niobium is in many ways similar to its predecessors in group 5. It reacts with most non-metals
at high temperatures: niobium reacts with fluorine at room temperature, with chlorine and
hydrogen at 200 °C, and with nitrogen at 400 °C, giving products that are frequently interstitial
and nonstoichiometric [44]. The metal begins to oxidize in air at 200 °C [45], and is resistant to
corrosion by fused alkalis and by acids, including aqua regia, hydrochloric, sulphuric, nitric and
0
(πμ (0)) 1 2 H
From 0 C 2
φ
2 From
( )
( 2 )
0 0 2
4
0
C
C
H
H
π
φ μ
3 From ( ) ( )
(0)
0 0
k eff ξ
GL
λ
=
4 From ( ) B C Δ 0 = Ck T , assuming a week coupling limit for pure Nb
27. Chemical properties 27
phosphoric acids [44]. Niobium is attacked by hot, concentrated mineral acids, such as
hydrofluoric acid and hydrofluoric /nitric acid mixtures. Although niobium exhibits all the
formal oxidation states from +5 down to -1, its most stable state is +5 [44].
Niobium is able to form oxides with the oxidation states +5 (Nb2O5), +4 (NbO2) and +3
(Nb2O3), [45] as well as with the rarer oxidation state +2 (NbO) [46]. The most stable oxidation
state is +5, the pentoxide which, along with the dark green non-stoichiometric dioxide, is the
most common of the oxides [45]. Niobium pentoxide is used mainly in the production of
capacitors, optical glass, and as starting material for several niobium compounds [47]. The
compounds are created by dissolving the pentoxide in basic hydroxide solutions or by melting it
in another metal oxide. Examples are lithium niobate (LiNbO3) and lanthanum niobate
(LaNbO4). In the lithium niobate, the niobate ion NbO3
− is not alone but part of a trigonally
distorted perovskite-like structure, while the lanthanum niobate contains lone NbO4
3− ions [45].
Lithium niobate, which is a ferroelectric, is used extensively in mobile telephones and optical
modulators, and for the manufacture of surface acoustic wave devices. It belongs to the ABO3
structure ferroelectrics like lithium tantalate and barium titanate [48].
Niobium forms halogen compounds in the oxidation states of +5, +4, and +3 of the type
NbX5, NbX4, and NbX3, although multi-core complexes and substoichiometric compounds are
also formed [45; 49] Niobium pentafluoride (NbF5) is a white solid with a melting point of 79.0
°C and niobium pentachloride (NbCl5) is a yellowish-white solid (see image at left) with a
melting point of 203.4°C. Both are hydrolyzed by water and react with additional niobium at
elevated temperatures by forming the black and highly hygroscopic niobium tetrafluoride (NbF4)
and niobium tetrachloride (NbCl4). While the trihalogen compounds can be obtained by
reduction of the pentahalogens with hydrogen, the dihalogen compounds do not exist [45].
Spectroscopically, the monochloride (NbCl) has been observed at high temperatures [50].The
fluorides of niobium can be used after its separation from tantalum [51]. The niobium
pentachloride is used in organic chemistry as a Lewis acid in activating alkenes for the
carbonylene reaction and the Diels-Alder reaction. The pentachloride is also used to generate the
organometallic compound niobocene dichloride ((C5H5)2NbCl2), which in turn is used as a
starting material for other organoniobium compounds [52].
28. 28 NIOBIUM PROPERTIES
Figure 2.1: Niobium pentachloride (NbCl5)
Other binary compounds of niobium include niobium nitride (NbN), which becomes a
superconductor at low temperatures and is used in detectors for infrared light, and niobium
carbide, an extremely hard, refractory, ceramic material, commercially used in tool bits for
cutting tools. The compounds niobium-germanium (Nb3Ge) and niobium-tin (Nb3Sn), as well as
the niobium-titanium alloy, are used as a type II superconductor wire for superconducting
magnets [53; 54]. Niobium sulphide as well as a few interstitial compounds of niobium with
silicon are also known [44].
2.4 Electrochemical properties
Nb is classical example of refractory metals. Thermodynamically Nb is very unstable so
it is covered by strong film of oxides. Most stable is Nb2O5. On a Figure 2.2 is shown Pourbaix
diagram which explains why there is no way to avoid oxide formation during Nb dissolving.
Only one way how is possible to dissolve Nb is to break oxide film for example using fluoride
anions. Table 2.3 shows reactions which can run according to Pourbaix diagram and gives their
equations. Nb situated in second group of metals overvoltage [55]
Electrodissolving/electroplating overvoltage is 10…100mV and exchange current density 10-
3…10-4A/cm2.
29. Electrochemical properties 29
Figure 2.2: Diagram E – pH for system Nb –H2O; 1 – equilibrium Nb/NbO; 2 - equilibrium
NbO/NbO2; 3 - equilibrium NbO2/Nb2O5; a – electrolytic hydrogen evolution; b – electrolytic
oxygen evolution.
№ Reaction Line
1 Nb+H2O→NbO+2H++2e- E=-0,733-0,0591⋅pH
2 NbO2+H2O→NbO2+2H+2e- E=-0,625-0,0591⋅pH
3 2NbO2+H2O→Nb2O5+2H+2e- E=-0,289-0,0591⋅pH
a H++2e-→H•
H2O+e-→H•+OH-
(2H•→H2)
E= -0,0591⋅pH
b 4OH-→2H2O+O2+4e
4OH-→2H2O+O2+4e
E= 1,23 - 0,0591⋅pH
Table 2.3: Reaction which are present on Figure 2.2.
30. 30 NIOBIUM PROPERTIES
№ Reaction E0, V
1 4OH-→2H2O+O2+4e +0,8
2 2Cl-→Cl+2e +1,35
23 ROH+e→RO-•+H• 0,0
4 2H2O+O2+4e→4OH- -0,4
5 Nb3
+ +3e- → Nb -1,1
6 RNH2+e→RNH-•+H•
7 Nb→Nb5++5e- -0,96
8 Nb→Nb3++3e- -1.1
9 2Nb+5Cl2→2NbCl5 -
10 NbCl5+4Н2О→5HCl+Н3NbO4 -
Table 2.4: Reactions which can run on Nb electrode and their potentials.
Niobium is totally passivated in urea melts. Its passivation in urea-chloride melt is also
rather strong and the depassivating action of Cl- ions is insufficient do dissolve this metals [56;
57]. The electrochemical behavior of Nb dissolution in urea-chloride melt has some features.
There is no Nb dissolution during first polarization (Figure 2.3, curve 1). Earlier was shown that
only after reaching transpassive potential region, where a reactive compound (presumably NCl3)
is formed which is the electrode surface depassivator, Nb dissolution wave appears at the
backward sweep. Nb dissolution may be observed at the forward sweep in subsequent cycles
(Figure 2.3, curves 2-4). The cathodic reduction of Nb(V) ions formed in the melt upon
electrochemical dissolution takes place only in Nb electrode (in contrast to inert Pt and glassy
carbon electrodes) after electrode prepolarization to the anodic region. The cathodic wave
corresponds to the recharge of Nb(V) – Nb(IV) ions. We failed to detect the formation of ions in
the lowest oxidation state(by electrochemical spectroscopic methods). Nb(V) – Nb(IV) ions are in
the melt in the form of chloride complexes, such as [NbCl6]- and [NbCl6]2-.
31. Techniques of Nb surface finishing 31
Figure 2.3: The anodic part of the cyclic voltammogram taken at a Nb electrode in the urea-
NH4Cl melt, t-130°C, scan rate 0,1 V/s
2.5 Techniques of Nb surface finishing
To improve the cavity performance it is necessary to reduce the surface resistance as
much as possible. To achieve this goal each Nb cavity undergoes to a series of successive
treatments (mechanical polishing, buffered chemical polishing, electropolishing, annealing).
They will be described in detail in chapter 3 .
Due to the pillbox-like shape of the cavity, chemical or electrochemical etching is the
most efficient technique for Nb surface finish. Etching to a depth of 100 to 400 μm is believed to
be enough to remove the mechanically damaged layer [58]. Two widely practiced etching
techniques are buffered chemical polishing (BCP) and electropolishing (EP) [59]. A BCP
process is usually performed in a typical solution of 1:1:1 or 1:1:2 (volume ratio) HNO3 (69%),
HF (49%), and H3PO4 (85%). The process is performed for a time sufficient to remove the layer
containing mechanical damage and contaminations. BCP commonly results in Nb dissolution at
a rate of 10 μm/min and a final surface roughness of 2 to 5 micron [60; 61].
The final surface finish is EP [62]. Cavity fabrication by EP is also known as “Siemens
method” because it was Siemens Company that firstly employed EP to treat SRF cavity surface
in the 1970s. Researchers in KEK further developed this technique and claimed that the
32. 32 NIOBIUM PROPERTIES
improved SRF cavity performance – such as the higher acceleration gradient – would be
achieved by EP over BCP [63]. This discovery has been confirmed by other laboratories that
were also investigating this process [16]. The currently accepted EP process for Nb surface
treatment is performed in a solution of HF (49%) and sulfuric acid electrolyte (98%) at volume
ratio of 1:8 to 1:10. During the EP, the Nb cavity is polarized anodically in an electrolytic cell at
temperature of 30oC to 40oC. The cathode is an aluminum rod with high purity. The area ratio of
anode and cathode is 10:1.The applied voltage is usually from 12 to 25 V and causes a current
density of 30 to 100 mA/cm2 [64]. EP results in a corrosion rate—around 0.5 μm/min—that is
lower than BCP but with a much better surface finish, especially at a microscopic scale. It has
been accepted widely that the best EP condition occurs under the voltage within the range of
limiting current plateau and that parameters such as electrolyte concentration, electrolyte
temperature, and viscosity strongly impact the surface finish [65; 66].
2.5.1 Hydrofluoric acid-based system
Nb performs a large negative free energy and is highly reactive toward oxygen [67; 68;
69]. In an aqueous electrolyte, it is easy for Nb to react with water molecules to form non soluble
niobium pentoxide (Nb2O5) by the reaction:
2Nb+5H2O → Nb2O5+10H++10e− (2.1)
The thickness of oxide layer with Nb2O5 is about 2 to 6 nm [70]. Suboxides such as
NbO2, NbO, and Nb2O are observed to form between the Nb2O5 outer layer and the underlying
Nb surface [71]. In additional to its negligible solubility in water, Nb2O5 is difficult to dissolve in
majority of acids as well. The oxides form a stable protective film on metal surface, thus prevent
further polishing of the metal surface during EP in aqueous electrolytes [72].
Hydrofluoric acid (HF) has good ability to destabilize Nb2O5 with the following reactions
to form soluble niobium fluorides and niobium oxifluorides:
Nb2O5+14HF→2H6NbO2F7+H2O (2.2)
Nb2O5 +12HF→2HNbF6+5H2O (2.3)
Nb2O5+10HF→2NbF5 + 5H2O (2.4)
Nb2O5+10HF→ 2H6NbOF5+3H2O (2.5)
HNbF6 + HF → H2 NbF7 (2.6)
The presence of HF is necessary in practical electrolytes for EP processes of Nb.
However, for a one single-cell cavity (e.g., the 1.5GHz single-cell cavity in Jefferson Lab)
treatment at least needs 1 liter of HF is used. It must be carefully managed to prevent human
33. Techniques of Nb surface finishing 33
exposure and must be disposed in environmentally appropriate way. At present, about 300 five-to
nine-cell cavities are processed per year in Jefferson Lab. This is a manageable concern.
However, ILC will require the operations capable of processing over 20000 nine-cell cavities per
year. The tremendous cost of managing large amounts of HF demands the development of HF-free
electrolytes.
2.5.2 Sulfuric acid-methanol electrolytes
One of alternatives found for Nb electropolishing is sulfuric acid solution in methanol.
Methanol is wildly used as a solvent instead of water [73; 74]. Piotrowski et al report the
successful EP of tantalum (Ta) and Titanium (Ti) by sulfuric acid-methanol electrolytes [75; 76].
The nature of sulfuric acid-methanol electrolytes is still under investigation. The best surface
finishing was obtained under mass transport limiting current. The value of limiting current
decreased as the concentration increased and the temperature decreased [75; 76]. The observed
current decrease with increasing concentration is suggested to be due to the corresponding
decrease in solubility of metal ions. Compact film was characterized to explain the mass
transport mechanism. One of the advantages of methanol-based electrolyte is the much-decreased
water content; therefore, the formation of Nb2O5 is expected to be avoided. Piowtroski
observed the current reduces by adding water into the methanol-based electrolyte – when the
water content in a 3 M sulfuric acid-methanol electrolyte increased from 0.02wt% to 5wt%, the
current during Ti EP decreased approximately 75 percent (about 0.8 A/cm2 to 0.2 A/cm2). When
the water content reached 10wt%, the Ti anode became passive. It is important to use sulfuric
acid with a weight ratio as high as possible and prevent it from water condensing from air. On
the other hand, Nb has a very close chemical property to Ta, so it is promising to electropolish
Nb in the methanol-based electrolyte.
34. 3
4
cel
Ob
pe
me
sm
pro
ad
3.2
me
3.1 T
The sp
ll is charac
bviously th
rformance,
echanical p
mooth and fr
In ord
ocess, we u
d hoc for larg
The 6
2, plugged u
edia pieces
3 St
tandard s
Tumbling
pinning pro
cterized by
he internal
especially
processing c
ree from con
der to remov
use a compa
ge cavities.
cess implie
the presen
surface fin
y at high
can contam
ntaminants.
ve surface r
act and port
e 3.1: Comp
y is filled w
ed to the ma
he metal su
Figur
GHz cavity
up and fixe
can erode th
STANDA
surface tr
ARD SURFA
reatment o
s material s
nce of evid
nishing of a
fields. Mo
minate the u
.
roughness an
table tumble
ACE TREATM
of 6 GHz
surface defe
dent vertica
resonant
oreover the
used mater
MENT OF 6
cavities
ects, stress a
al scratches
structure i
e lubricant,
rial. The id
nd contami
er in spite o
pact tumblin
with a certai
achine. The
urface in a u
GHZ CAVI
and dislocat
due to the
s directly c
necessary
dea is to m
nations intr
of the bigge
ng system fo
n number o
tumbler m
uniform, con
ITIES
tions. The c
e used man
correlated t
y for the m
make the su
roduced dur
er and comp
for small res
of abrasive a
makes the ca
ntrollable an
cavity
ndrel.
to its
metal
urface
ring the spin
plicated des
sonators.
agent piece
avity rotate
nd reliable w
nning
igned
s (media) F
so that the
way.
Figure
small
35. Tumbling 35
Different materials could be used for this kind of mechanical polishing: for example
small SiC triangular shaped blocks, 5 mm sphere of yttria stabilized zirconium dioxide and
flakes of Al2O3 and SiO2 powders embedded in a polyester matrix.
Figure 3.2 Three types of different abrasive media.
1 – SiC; 2 – ZrO2; 3 – Al2O3 + SiO2
Silicon carbide is a very hard material and it can be used for the first low level
mechanical polishing. ZrO2 is a high density material and can be used for the intermediate
smoothing. Al2O3 plus SiO2 (in PET) flakes are soft and can be used for the final surface
finishing.
During a mechanical treatment, for each cavity, it is easy to stop the process and monitor
the smaller resonator weight change with a balance and internal surface finishing with the help of
a miniature camera (visible on Figure 3.3).
36. 3
6
an
co
Th
Po
lig
po
fix
mi
dis
ba
tre
On
Figure 3.3
dea is to ch
ouch the sm
erfaced firm
nected by an
he mobile t
e the only
n defects re
tor, so the re
mera tool ca
along the
The id
ny risk to to
mputer inte
hey are conn
ositioning th
ghtening are
ositioning on
xed protract
iniature cam
splacement
asis.
Using
this proce
ation to per
e top part o
m part on
eatment dura
On the
n the bottom
: The minia
eck an even
mall cavity
m base and a
n optical fib
tool near th
necessary
eliable a su
esonator rot
an be moved
cavity axis
edure it’s e
rform the be
on the right
the left a
STANDA
ARD SURFA
ture camera
ntual defect
y internal su
mobile to
bers cable. T
he point of
operations
upport syste
tation angle
d forward, b
can be eas
ACE TREATM
a tool used f
t evolution
urface. It is
ol equipped
The acquire
f interest, fo
to obtain
em has to b
e (relative to
backward, u
sily measur
easy to cho
est internal s
a picture o
picture of
MENT OF 6
for the cavi
after each p
s composed
d with the o
ed images m
focusing and
the desired
be used. Th
o its axis) c
up and down
red with th
oose the ri
surface finis
of the cavity
the same p
ity inspectio
polishing tr
d by two d
optical and
magnificatio
d eventuall
d image. To
he latter is
can be easily
n inside the
e ruler fixe
ght media
shing in a fe
y cell befor
place of the
and to est
few steps.
re the mech
e cell after
GHZ CAVI
ITIES
on.
reatment wi
different pa
lighting dev
on is around
ly correctin
o make the
equipped w
y measured
e cavity. The
ed to the sy
ithout
arts: a
vices.
d 60x.
ng the
e tool
with a
d. The
e tool
ystem
tablish the
anical polis
r the mecha
right
shing.
anical
37. Lapping 37
polishing. The surface after the treatments appears smoother than before. The vertical scratches
due to the used mandrel have disappeared.
3.2 Lapping
After all mechanical operations follows cavities flanges preparation. Flanges surface must
be flat and polished to prevent leaks on cavities rf testing stand. For this aim is using polishing
circle with different abrasive papers wetted with water. First is paper 400 for rough treatment
which produces flat surface. Next will go 600, 800, 1000 which will decrease roughness. Final is
1200 with using alcohol instead of water. After lapping is necessary to make precise washing of
cavity in ultrasound bath with soap in few steps and rinsing.
Figure 3.4: Lapping plant.
38. 38 STANDARD SURFACE TREATMENT OF 6 GHZ CAVITIES
Figure 3.5: Difference between flanges surface before(1) and after(2) lapping.
3.3 BCP
Following the classical and well known surface treatments general protocol of large
cavities, after the mechanical polishing the procedure counts a chemical polishing. Chemical
treatments are performed to smooth further on the cavity surface, to remove the possible niobium
sub-oxide and contaminants.
To perform the traditional surface chemical treatments, buffer chemical polishing (BCP)
and electrochemical polishing (EP), on a 6 GHz cavity can be used a small system as the one
reported in Figure 3.6.
In particular can be seen on the right a 6 GHz cavity installed in vertical position,
equipped with special flanges for EP. The acid flux is directed from the bottom to the top of the
cavity in order evacuate the hydrogen, produced during the process, quickly. The 3-way valves
are useful to invert the flux direction.
39. BCP 39
Figure 3.6: Stand for BCP and EP.
1 – cavity; 2 – anode contacts; 3 – cathode contact; Blue indicator – direct flow, red – indirect.
For buffer chemical polishing are used simple holed PVDF flanges as is shown in Figure
3.7.
Figure 3.7: Details of the cavity closing system for buffer chemical polishing.
1- 6GHz cavity;2 – SS half round rings; 3 – BCP flanges.
40. 40 STANDARD SURFACE TREATMENT OF 6 GHZ CAVITIES
In the case of electrochemical polishing are used particular PVDF flanges able to hold a
aluminum cathode conveniently designed as reported in Figure 3.8.
The flanges are expressly designed to obtain the highest acid flow through the cavity to
allow hydrogen bubbles, produced during the oxi-reduction reaction, to escape freely.
The evaluations of damaged layer thickness produced by the spinning process could be
vary from 150 to 250 μm. For this reason it is convenient to remove with BCP/EP at least 300
μm: in average this thickness corresponds to about 30 g of removed material.
3.4 EP
6GHz cavities are polished on classical EP solution with acid ratio HF:H2SO4 . During
the process solution is pumped throw the cavity from bottom part to top part for a easier
removing hydrogen from the cavity which is forming on cathode. After the half of process time
cavity is swapped the position on 180 for flux substitution. Controling parameter of EP process
is electrical tension between cathode and cavity. Usually electrical tension is 10…20V.
Figure 3.8: Details of the cavity closing system for electropolishing.
1 – 6GHz cavity;2 – SS half round rings; 3 – EP flanges; 4 - aluminum cathode; 5 –
holed guiding ring
Figure 3.9 shows an example of EP process result on 6GHz cavity which was produced
and electropolished in SC laboratory in LNL INFN.
.
42. 42 APPARATUS AND PROCEDURES
4 Apparatus and procedures
4.1 Potentiostat instrumentation
A potentiostat is an instrument that provides the control of the potential difference
between the working electrode and the reference electrode [77]. The potentiostat implements this
control by applying current into the cell between the working electrode (WE) and the counter
electrode (CE) until the desired potential between the working electrode and the reference
electrode (RE) is reached. Figure 4.1 shows the schematic diagram of a potentiostat with
computer control.
In an electrochemical cell for EP, the working electrode is the electrode to be polished. A
well-working reference electrode should have a constant electrochemical potential. In this work
Nb wire using like a RE. It is not the best reference but is simple and it is enough to understand
kinetic especially when potential reaches to 20V. The counter electrode completes the cell
circuit. In this work graphite rod was used like CE. Working electrode for this work was made
from 3mm diameter Nb rod which was isolated on lateral surface with epoxyresin. Bottom part
of electrode was polished in way which is using for 6GHz cavities flanges.
Figure 4.1: Schematic diagram of a potentiostat.
4.2 Anodic polarization scan
Polarization is measured as overpotential, i.e. as a change in potential from the
equilibrium half-cell electrode potential or the corrosion potential. During an anodic polarization
scan the potential on the working electrode is varied linearly with the time and the change in
current is recorded. Figure 4.2 shows a typical anodic polarization curve. In region B, the active
region, metal oxidation is the dominant reaction. When the potential increases above the
passivation potential (point C), the current will decrease rapidly to region E, the passive region.
When the potential reaches a sufficiently positive value (point F), the current will increase
rapidly to region G, the transpassive region. Region G may be another process which has
43. Solutions and samples preparing 43
equilibrium potential equal to potential in the point F. Classical example which can be found for
this situation is Fe (in the sulfuric acid water electrolytes) Ni, Nb. Experimental polarization
curve may show some - but not necessarily all of the features described in figure below. If curve
will go through the way H than it is possible to see the electrode polishing. Usually this type of
curve is a goal for research in field surface treatments. G can be obtained on metals which do not
passivate. A classical example is Cu (in acid sulfate water electrolyte) or Fe (in water sulfuric
acid electrolytes in presence of Cl--ions).
Figure 4.2: Schematic diagram of an anodic polarization.
4.3 Solutions and samples preparing
Choline chloride – urea melts are prepared fresh for all experiments. Normally was
prepared 2 liters of solution. For this amount of solution is used a 5 liters baker. ChCl(calculated
quantity of weight) was put on the bottom and after urea in mol proportion. This mixture was
placed on heater and was heated slowly to temperature 120°C. Is necessary to keep melt at this
temperature at least half an hour for the evaporation of residual water.
In this work it was determined that it is necessary to pass some quantity of electricity
throw solution using Nb anode. At the beginning the anode potential should be more than 50V. If
it is lower than it will be observed the Nb passivation instead of dissolution. This behavior is not
understood now.
Samples were cut from residual material which was left from 6GHz production. Sample
size 5cm lengs and 3cm width. Samples were pulled down in a half of length inside solution.
44. 44 APPARATUS AND PROCEDURES
Cleaning of samples was in next order: washing with dichloromethane. Washing in ultrasound
with soap, washing in ultrasound in, rinsing demonized water, drying with alcohol and acetone
using nitrogen blowing.
4.4 Two electrodes system
Experiments were done in a backer with quantity of electrolyte ranging from 200 to 400
ml. the solution temperature was increased using heater with thermocouple covered with PTFE.
The electrolyte is always stirred (Figure 4.3). Electric power was taken from power supply HP
Alintel using automatic control software(Figure 4.4) designed at SC Lab LNL INFN written in
Labview 7.1.
Figure 4.3: Investigation samples system
1 – heater; 2 – beaker;3 – anode(WE); 4 - sample holder; 5 – support; 6 –thermocouple covered
by PTFE; 7 – cathode(CE); 8 -stirrer .
45. 6GHz cavity electropolishing system in ionic liquids 45
Figure 4.4: Automatic software for controlling potential.
4.5 6GHz cavity electropolishing system in ionic liquids
6GHz cavities electropolishing was done in vertical way with pumping solution through
the cavity. Cavity is used like a chamber.
Cavity 1 (Figure 4.5) is mounted on support. Holed cathode is immersed inside the cavity
connect to electrical contact 2. Cavity is connected by flanges screws to a anodic contact 3.
Cathode is centered by flanges. Flanges have the same design like flanges for classical EP.
Thermocouple 4 is immersed inside the backer 8. with solution. Cavity is connected from
bottom part to the output from the pump 9 and up side to the tube which brings solution back to
the backer.
4.6 Stylus profilometry
Profilometry is a method used to measure the profile of a surface, in order to quantify its
roughness. The surface roughness values discussed in this dissertation were measured by contact
profilometry. A diamond stylus scans laterally across a sample surface under a specified force
for a specified distance. The stylus detects small variations in vertical displacement as a function
of lateral position. A typical profilometer is sensitive to vertical height variations ranging from
10 nm to 1 mm. Scan speed, contact force, and stylus radius all affect the lateral resolution. A
46. 46 APPARATUS AND PROCEDURES
typical stylus radius ranges from 5 to 25 μm. The profilometer used in this work was Veeco
Dektat 32.
Figure 4.5: 6GHz cavities electropolishing system.
1 – cavity; 2 – cathode contact; 3 – anode contact; 4 – thermocouple; 5 – input pump; 6 – input
cavity(output pump); 7 – output cavity; 8 – baker with ionic liquids; 9 – pump.
The scan length was 1000 μm. Scan duration was 13,0 sec. The contact force was 10 mg.
The stylus radius was about 5 μm. Measure range – middle was 65000nm. Analyses were done
using average roughness (4.1):
Σ=
=
z
a i N
i
N
R
1
1
(4.1)
where zi illustrated on Figure 4.6
47. Stylus
s profilometr
zi – is a diff
All samp
age value by
avera
ry
Figure 4.
tween measu
fference bet
ples were m
y equation (
measured 6
4.2) and er
4.7: Scheme
Figure 4
ሺܯ݁݀݅ݑ݉ሻ
σ
6: Example
ured value a
e of surface p
and average
times as is
rror of meas
s shown on
suring by eq
e of profilom
metry analy
݉ ൌ Σಿ ௌ
ܯ݁݀݅ݑ݉
ሻ ൌ ට ଵ
ேିଵ
Σ
సభ
ே
ሺܵܿܽ݊
ே
ୀଵ
profile.
ed measure
ed values on
a Figure 4
quation (4.3
4.7. After w
).
ysis perform
mance.
݉ሻଶ
െ ܯ݁݀݅ݑ݉
47
n length l.
were calcula
ated
(4
4.2)
(4
4.3)
48. 48 APPARATUS AND PROCEDURES
where N is the number measures. In the Figure 4.8 some examples of roughness profiles are
shown. Three samples have been treated in different ways. The electropolished one is most
smooth.
Figure 4.8: Surface profiles of the raw surface (Raw), the mechanically polished (MP) surface,
and the electropolished (EP).
49. Stylus profilometry 49
5 Experimental part
Is well known that Nb is covered with solid oxide film. Formation speed of this oxides
isso fast that even at anodic polarization on aggressive concentrative environments like nitric,
sulfuric and alkaline water contained solutions current doesn’t pass. Instead of dissolution there
is anodization (Figure 5.1 a) or small dissolving with pitting formation(Figure 5.1 b). Adding
hydrofluoric acid destroys oxides and provides dissolution. As much water inside the solution as
more difficult dissolves metal and more hydrofluoric acid needs.
a) b)
Figure 5.1: Results obtained in water solutions.
On previous work [78; 79; 80; 81] found that in Choline Chloride – urea melt is possible
to dissolve Nb but dissolving is very sensitive to geometrical factor of the electrochemical cell.
One of the trick points is that impurities of water are insignificant because of temperature which
is using on the process higher than boiling temperature of water. So there is two things which
must be solved:
1. Find approach to break oxides film.
2. Provide equal speed dissolution on all surface of anode with viscous film formation
during the electrolyses.
Has been found that there is a possibility to dissolve Nb using high overpotential in 1-4
ChCl-urea melt. First have been put 30V into the 2 electrode system and have been obtained
current and dissolving of Nb together with gas formation on back side of sample(Figure 5.2).
There are pitting and oxidized spots on the places where gas was evaluating. When we have put
65V we observed less gas evaluating on both sides of the electrode and yellow film formation
around the electrode – viscous film. Almost all surface became polished (Figure 5.3). There are
some not deep pitting on the front side and not treated part in the back side. Overvoltage heats
electrolyte in few seconds from 120°C till 190°C and higher. Which has very bad effect on
stability of melt (Figure 5.5).
50. Experimental part 50
Figure 5.2: Front(left) and back(right) of
sample electropolished with overpotential
30 V.
Figure 5.3: Front(left) and back(right) of
sample electropolished with overpotential
65V.
Figure 5.4: Degradation of solution.
From thermodynamic point of view applying potential to electrode is to much big so
that’s why was performed series of experiments in order to find approaches to decrease
electrical tension and may by current density. Later was observed influence of presence S-NH2-
containing compounds on EP. Mostly, practical interest has Sulfamic acid.
5.1 Three electrodes system
5.1.1 Voltametry
In order to understand what is happening on Nb electrode in ChCl – urea melts were
made voltametry and polarization curves tests in the equal solutions but with different
51. Th
hree electrod
w
do
des system
working elec
one tests on
go
re
5.
el
in
ac
an
ur
af
th
hy
ctrodes. Firs
n Nb electro
ametry is fas
d in a which
fining the p
n voltammo
ChCl-urea m
Volta
oing on and
egime is def
5 is shown
lectrode in C
5.5: Voltam
Urea as 1-4(
mic acid de
solution ano
in to 1-4 C
s overvoltag
lectrodes ha
igure 5.6). M
versus Nb w
l current de
tween straig
Figure 5
1 – ChCl-U
Sulfam
nvestigated
cid adding i
nd increases
Nb el
rea melt (Fi
fter 3 volts v
he potential
ysteresis bet
st was glass
de.
ster than po
h potential r
process wha
ogram whic
melt.
sy carbon e
electrode an
olarization c
region. Pola
at is the spe
ch illustrate
mmogram ta
(mol); 2 - C
ecreases ano
odic curren
ChCl-urea m
ge.
as a differen
Main differ
wire in corr
ensity incre
ght and back
nd after in t
curves so it
arization cu
eed of proce
es Sulfamic
ken on glas
the equal co
t gives poss
urves are slo
ess in all po
c acid beh
ssy carbon e
mV/sec.
as 1-4(mol)
s current de
carbon WE
ses electroch
100m
ChCl-Urea a
odic proces
nt on glassy
melt decreas
nt form of
rence is in m
responding s
eases durin
k sweep.
sibility to ob
ow but show
otential rein
aviour on
electrode vs
in presence
ensity. Vers
E starts pass
hemical win
the curve t
much bigge
solution. In
ng some tim
s. Nb wire, s
e of 30g/l Su
sus Nb wire
sing earlier
ndow in an
than glassy
er overvolta
n high voltag
me. There
carbon in
age, current
ge region w
is much b
5
51
onditions w
were
bserve wha
w what kine
nge. On Figu
glassy carb
at is
etic
ure
bon
scan rate
ulfamic acid
e dropped in
. So, Sulfam
nodic direct
d.
nto
mic
ion
the 1-4 Ch
t starts to fl
with decreas
igger posit
Cl-low
ing
tive
52. 5
2
igure 5.6: V
Fi
ure
wh
po
wa
ele
Voltammogr
Figure
ea melt. Su
hen current
olarization t
as possible
ectrodes wit
ram taken in
on glassy c
1 –
e 5.7 illustra
lfamic acid
t density i
o 14V will
to put bigg
thout using
n 1-4 (ChCl
carbon elect
ates influen
d decreases o
is not enou
not break
ger potentia
BCP.
l-Urea) mel
trode; 2 - on
nce of Sulfam
overvoltage
ugh high
passive film
l (65V) and
lt vs. Nb wir
n Nb electro
mic acid on
e and revers
electrode s
m(Figure 5.
d were obse
EXPERIME
ENTAL PAR
re, scan rate
ode.
n Nb anodic
se slope. Th
starts to pa
7 curve 3)
erved curren
RT
e 100mV/se
c dissolving
here is anoth
assivate an
. In 2 elect
nt flowing
c.
g in 1-4 ChC
her key poin
nd even ne
trodes syste
on passivat
Cl-nt,
ext
em
ted
53. Th
hree electrod
des system
5.7: Voltamm
Urea as 1-4
P; 3 - ChCl-
Figure 5
1 – ChCl-U
after BCP
po
(F
ob
st
ag
sim
5.1.2
Intere
Polarizat
esting phen
curves was
curve 1), 1
sulfuric ac
electropolis
elative Nb
echanism to
olarization
Figure 5.8 c
btained in
ability of e
ggressive re
milar in me
mogram tak
(mol); 2 - C
-Urea as 1-
ken on Nb e
ChCl-Urea a
4(mol) in p
tion curves
nomena may
s observed
1-4 ChCl -
cid – meth
shing proce
oxides film
ChCl – ure
electrode vs.
as 1-4(mol)
resence of 3
method
y be obser
same order
urea melt
hanol electr
ess [82]. 49
m. Sulfuric
ea solution b
. Nb wire, s
in presence
30g/l Sulfam
rved on Nb
r of current
with 30g/l
rolyte(Figur
9% HF wa
acid – met
because of t
can rate 10
e of 30g/l Su
mic acid afte
b WE in d
t density of
SA (Figur
re 5.9 gree
ater solution
thanol elect
their also us
different sol
f EP proces
re 5.8 curv
en line) du
n was chos
trolyte prob
se high elec
5
53
00mV/sec.
ulfamic acid
d
er curve 2.
lutions. Us
ss in 49%
ve 2) and d
uring studd
sen like m
bably are v
ctrical tensio
ing
HF
data
ing
ore
ery
on.
54. 54 EXPERIMENTAL PART
Figure 5.8: Polarization curves taken on Nb electrode vs. Nb wire.
1 – in 49% HF; 2 – in 1-4 ChCl – urea melt with 30g/l SA
Figure 5.9:Current density – time dependence observed in 0,1M Sulfuric acid solution in
methanol at Nb electrode with tension 22V for different temperature.
55. Two electrodes system 55
5.2 Two electrodes system
5.2.1 Influence of dissolved NbCl5
In this chapter is observed dependence from quantity of Nb inside solution. In order to
determine this dependence was prepared fresh 1-4 ChCl – urea solution and equal samples
with working area 15cm2. All samples were weighed before and after 5 min of
electropolishing. Test was done in galvanostat mode with 0,6 A/cm2 for a 10-20 seconds in
overvoltage and 0,3 A/cm2 during all process. Quality of surface was determined with
profilometry measuring and results is presented like roughness – dissolved Nb concentration
(Figure 5.10).
First sample roughness is not shown on a figure because it is more 7000nm.
Roughness of samples electropolished with concentrations of dissolved Nb more than 4g/l are
less than raw Nb and sometimes even close by average value to roughness of surface
electropolished with classical EP. There is a huge difference between roughness of front and
back sides.
0 2 4 6 8 10 12
C(Nbdissolved), g/l
Front Back Classical EP Raw Nb
Figure 5.10: Roughness dependence from dissolved Nb concentration
2000
1800
1600
1400
1200
1000
800
600
400
200
0
In according to Figure 5.10 is obviously that electropolishing in ChCl – urea is
Ra, nm
comparable to Classical EP after dissolving of Nb in quantity 4 g/l. There is not uniform
distribution of current between front and back side of samples.
56. 56 EXPERIMENTAL PART
5.2.2 Sulfamic acid – first success
Providing uniformity of current density was performed through searching surface
active compounds which could be added to melt in a reasonable quantity without increasing
melting/boiling point of melt. Were performed tests using alcohols (Butanol, ethanol) organic
acids(tartaric, oxalic), butyl acetate but results were not satisfied. After was decided to make
try on light oxidizer. Choice fall down to Sulfamic acid and result was enough good so was
performed series of tests to determine its influence on Nb anodic dissolution in 1-4 ChCl –
urea melt.
Was used galvanostat mode, overvoltage 65V for 10-20 seconds and time of process
5min as in previous experiments. Due to electropolishing process dependents from dissolved
Nb concentration was performed preliminary dissolving of Nb.
First was determined optimal concentration of Sulfamic acid. Using same prepared
before matrix melt were done electropolishing of samples with different concentration of
Sulfamic acid. According to Figure 5.11 is understandable that with increasing of Sulfamic
acid concentration roughness of front and back side of samples passes through the minimum
which lies in region near SA concentration 30g/l. Front side roughness is comparable to
roughness with Classical EP and back side roughness is even less.
800
700
600
500
400
300
200
100
0
0 10 20 30 40
Figure 5.11: Roughness dependence from Sulfamic acid concentration.
Ra, nm
C(SA), g/l
Front Back Classical EP Raw
57. Two electrodes system 57
Discovering Sulfamic acid influence was a great success for future development of Nb
EP process.
Next step was determining best working current density or in another worlds smaller
possible current density which will prove EP but with less heat generation.
For this test was used the equal to previous test matrix melt with Sulfamic acid
concentration 30g/l. All samples were yielded to overvoltage 65V. Roughness of sample as
function of current density is shown on a Figure 5.12.
0.0 0.1 0.2 0.3 0.4 0.5
Front Back Classical EP Raw Nb
Figure 5.12: Roughness dependence from current density.
900
800
700
600
500
400
300
200
100
0
Ra, nm
i, A/cm2
As against to concentration current density has more similar influence to front and
back roughness and passes through the minimum near 0,3A/cm2 as was .
When compounds composition of the solution and electrical parameters have become
determined again was checked influence of dissolved Nb. For this task was used the same
matrix solution with 30g/l Sulfamic acid and current density 0,3A/cm2 and 65V overvoltage
during 10-20 seconds. Results are presented on a Figure 5.13.
58. 58 EXPERIMENTAL PART
800
700
600
500
400
300
200
100
0
0 2 4 6 8
C(NbDissolved), g/l
Front Back Classical EP Raw Nb
Figure 5.13: Roughness dependence from dissolved Nb concentration.
Ra, nm
According to previous test of Nb concentration influence is understandable that there
is necessity in preliminary Nb dissolving in quantity more than 2 - 4 g/l.
The proofing of previous testes was roughness determining with different time of EP
process(Figure 5.14). Solution was prepared from the same matrix solution with previous Nb
dissolving. After was put 30g/l Sulfamic acid. All samples were weighed before and after the
EP process. Roughness of samples not strongly depended from time of the EP process but
after 30 min of the EP process difference between front and back of samples is the least.
Outward appearance of the samples is shown on a Figure 5.15. There is strong dissolving on
the borders with shape changing on sample which was treated 60 min. It says about fast
dissolving which can be determined from slope of line in coordinates time of treatment –
removed thickness (Figure 5.16). Thickness was calculated from difference of samples
weight.
59. Two electrodes system 59
0 10 20 30 40 50 60
Figure 5.14: Roughness dependence from process time.
800
700
600
500
400
300
200
100
0
Figure 5.15: Outward appearance of the samples electropolished with different time.
a – front; b – back; 1 – 5min; 2 – 10 min; 3 – 20min; 4 – 30min; 5 – 60min.
Ra, nm
t, min
Front Back Classical EP Raw Nb
60. 60 EXPERIMENTAL PART
h = 6,2⋅t
0 20 40 60
Figure 5.16: Removed thickness dependence from time of process.
450
400
350
300
250
200
150
100
50
0
Electropolishing in ChCl – urea is very fast, dissolving speed reaches 6,2 g/min. As is
shown on the Figure 5.16 for removing 400μm is enough only one hour instead of 15 – 20
hours using Classical EP.
5.2.2.1 Summary
9 Adding 30g/l Sulfamic acid in 1:4 choline chloride – urea melt gives possibility to
obtain brightness surface, without spots and pitting on the both sides of the sample.
9 The best result obtained with IL is comparable with the surface roughness obtained
with classical EP (Figure 5.17)
9 The back side roughness is the same to the front roughness: good current distribution
around the sample.
9 Main disadvantage is consisted from strong rising solution temperature which has
critical influence on solution stability and marginally on quality of cavities surface
quality. More about results obtained on 6GHz cavities electropolishing is written on
chapter 5.3.
h, um
t, min
h, um Classical EP Trend line
61. Two electrodes system 61
Figure 5.17: Surface maps of different treatments .
a – raw Nb; b – 10 min classical EP; c – 10 min IL; e – 60 min IL.
5.2.3 Influence of S and N containing compounds
When capacity for work with Sulfamic acid was determined was decided to look for
another regulators similar in nature. Choice fall down to ammonium sulfate, ammonium
sulfamate and ammonium persulfate.
5.2.3.1 Ammonium sulfate as alternative to Sulfamic acid
Galvanostate mode. i=0,3 A/cm2 with overvoltage 65V. t = 5 min
Sample 5 Sample 6 Sample 7
Electrolyte 1ChCl+4Urea, 10 min dissolving Nb. After adding 30g/L SA
C((NH4)2SO4), g/L 5,7 17 40
Ra(front), um - - 631±134
Ra(back), um - - 456±78
Table 5.1: Ammonium sulfate experimental data.
Using 40 g/l ammonium sulfate in 1-4 ChCl – urea melt is possible to treat Nb surface
with good current distribution but samples could have play of colors.
62. 62 EXPERIMENTAL PART
Front
Back
Figure 5.18: Samples treated in ionic liquid with ammonium sulfate
5.2.3.2 Ammonium sulfamate as alternative to Sulfamic acid
Galvanostate mode. i=0,3 A/cm2 with overvoltage 65V. Galvanostate mode. t = 5 min
Sample 61 Sample 62 Sample 63 Sample 64 Sample 64
C(NH4OSO2NH2),
g/L
10 20 40 50 50
Δm, g
0,482 0,439 0,397 0,412 0,526
Ra(front), um - - 262±62 447±86 685±209
Ra(back), um - - 259±73 300±75 166±26
Table 5.2: Ammonium sulfamate experimental data.
On Sample 64 is possible to work in automatic potentiodynamic mode using automatic
software. This fact gives ground of presence stable plateau.
63. Two electrodes system 63
Figure 5.19: Samples treated in ionic liquid with ammonium sulfamate
Using 40 g/l ammonium sulfamate in 1-4 ChCl – urea melt is possible to treat Nb
surface with good current distribution.
5.2.3.3 Ammonium persulfate
Automatic control potentiodynamic mode.
Solutin preparig:
1. Melting ChCl -Urea
2. Dissolving Nb
3. Adding Ammonium Persulphate.
Sample 66 Sample 67 Sample 68 Sample 69 Sample 60
C((NH4)2S2O8),
g/L
2 5 10 10 15
Δm, g
0,482 0,439 0,397 0,412 0,526
Ra(front), um - 1097±184 450±185 - 1485±385
Ra(back), um - 734±334 1613±466 - 290±45
Table 5.3: Ammonium sulfamate experimental data.
64. 64 EXPERIMENTAL PART
This regulator is very reactive and during dissolving it oxides ChCl – Urea melt.
Solution changes colour with increasing concentration of persulphate from light to dark
brown and generates foam . So is necessary to put persulfate slow with ubundant agitation.
Figure 5.20: Samples treated in ionic liquid with ammonium persulfate
Sample 71 Sample 72 Sample 73 Sample 74 Sample 755
C((NH4)2S2O8), g/L 10 11 12 20 20
Δm, g 0,482 0,439 0,397 0,412 0,526
Ra(front), um - 752±138 - - 1642±737
Ra(back), um - 662±232 - - 220±58
Table 5.4: Ammonium persulfate experimental data.
Adding PS is possible to work in automatic mode without overvoltage and with less
working potential. There is stable plateau in potential range 20…30V which replies to current
density 0,3 A/cm2 range.
5 Without stirring
65. Two electrodes system 65
Figure 5.21: Samples treated in ionic liquid with ammonium persulfate.
5.2.3.4 Summary – Comparison between N and S-containing compounds as Nb EP-regulator.
From each of 3 last chapters was chosen best surface quality sample and their data
were accommodated on a Table 5.5
Best results obteined on SA and Ammonium Sulphamate. Ammonium sulfate has own
advantage like most stable, simple and less corrosive compound. Ammonium Persulphate
gives a possibility to start electropolishing without overvoltages, but result on samples still
not satisfied. Probably it will be possible to use Persulfate and SA or Ammonium Sulfamate
togather.
66. 6
6
Su
Am
[Sa
Am
sul
[Sa
Am
pe
[Sa
vo
ter
po
me
5.2
C(
Ra
Ra
T
Substanc
ce
d
ulfamic acid
mmonium s
ample 7]
mmonium
lfamate
ample 63]
mmonium
rsulfate
ample 72]
sulfate
.5: S and N
Table 5
Solutio
on with Pe
3A/cm2 an
cal parame
ecres limit c
solution 1Ch
oltages (~0,
rmodynamic
ossible to de
eans using s
5.2.4
2.4.1 Melt
a)
Solutio
1. M
2. Di
3. Ad
i~0,3 A
(SA), g/L
a(front), um
a(back), um
Table 5.6: E
Influence
t ChCl : Ur
Sulfamic
on preparig
elting ChCl
issolving Nb
dding sulfam
A/cm2. Auto
Sam
m
m
Experimenta
Structural
l formula
containing
g regulators
ersulfate ev
nd 20V) wh
ter which w
current dens
hCl-2urea,
ven withou
hich brings
we not abl
sity using so
1ChCl-1ure
e of ChCl an
nd urea
rea = 1 : 2
acid
g:
l -Urea
b
mic acid.
omatic mod
mple 81
10
-
-
de. t = 5 mi
Sample 82
al data of sa
20
-
-
amples trea
Cwork,
30
40
40
10
g/L Ra(f
influence o
ut overvolta
s to heating
le to chang
olution with
ea,..
in
Sample
30
ated in1-2 C
front), um
2
274±26
63
31±134
2
262±62
75
52±138
on surface q
quality comp
age has hig
g of solutio
ge than cur
h less quntit
gh working
on. If pote
rrent is cin
ty of NH2-
e 83 Sa
mple 84
40
774±1749
346±160
melt in pres
- 17
-
EXPERIME
ChCl –urea m
ENTAL PAR
RT
Ra(back),
241±4
, um
1
456±7
8
259±7
3
662±23
parison.
32
g current a
ntial is mo
etic and it
groups whi
and
ore
is
ich
Sample 8
45
5
2252±19
1054±8
sence of SA.
82
24
.
67. Two electrodes system 67
Figure 5.22: Samples treated 1 -2 ChCl –urea melt in presence of SA.
Front
Back
The best surface quality has been obtained in melt with 40 g/L SA.
b) Ammonium persulfate
Galvanostate mode, i~0,3 A/cm2.
Sample 86 Sample 87 Sample 88 Sample 89
C(PS), g/L 5 7,5 10 12,5
Ra(front), um - 1640±479 1118±358 1929±659
Ra(back), um - 435±202 5373±170 432±270
Table 5.7: Experimental data of samples treated in1-2 ChCl –urea melt in presence of PS.
68. 68 EXPERIMENTAL PART
Front
Back
Figure 5.23: Samples treated 1 -2 ChCl –urea melt in presence of SA.
The best surface quality has been obtain in melt with 10 g/L PS.
5.2.4.2 Melt ChCl : Urea = 1 : 1
a) Sulfamic acid
Sample 91 Sample 92 Sample 93 Sample 94 Sample 95 Sample 96
C(SA), g/L 10 20 25 25 30 40
Ra(front), um - 755±459 1895±468 1242±206 1343±288 -
Ra(back), um - 1404±200 1655±679 779±296 380±94 -
Table 5.8: Experimental data of samples treated in1-1 ChCl –urea melt in presence of SA.
69. Two electrodes system 69
Front
Figure 5.24: Samples treated in 1 -1 ChCl –urea melt in presence of SA.
Back
2500
2000
1500
1000
500
0
20.0 25.0 30.0
Ra, nm
C(SA), g/l
Front Back Sample 94 Front
Sample 94 Back Classical EP Raw Nb
Figure 5.25: Roughness of samples treated in 1 -2 ChCl –urea melt in presence of SA.
70. 70 EXPERIMENTAL PART
b) Ammonium persulfate
Results are so bad that there was no reason to measure roughness on any of this
samples.
Front
Back
Figure 5.26: Samples treated in 1 -1 ChCl –urea melt in presence of PS.
5.2.4.3 Summary - Comparison between different composition of ChCl – Urea melts on
samples surface quality.
This tests was done to check possibility to decrease contents of urea in the melt. In
order to decreas current density by effect of breeding.
In first experiments on IL were observed that in 1-1, 1-2 and 1-3 melts (ChCl-Urea) is
possible to dissolve some Nb but samples look like polished only in 1-4 melt. Increasing of
samples surface quality has been observed In row 1-1, 1-2, 1-3, 1-4. This experiment shows
fundamental role of urea instead of ChCl on Nb electrode process. Also Tumanova reported
importance of urea in research of refractory metals electrochemical properties in Urea-NH4Cl
melt.
Collected dates for comparison are shown on a Table 5.9 and graphically Figure 5.27.
71. Two electrodes system 71
Substance Composition
ChCl : Urea Cwork, g/L Ra(front), um Ra(back), um
Sulfamic acid
[Sample 41] 1-4 30 1 96±48 256±22
Sulfamic acid
[Sample 84] 1-2 40 1774±87 346±80
Sulfamic acid
[Sample 95] 1-1 30 1242±23 779±10
Ammonium persulfate
[Sample 72] 1-4 10 752±14 662±23
Ammonium persulfate
[Sample 88] 1-2 10 1118±36 537±85
Ammonium persulfate 1:1 - - -
Table 5.9: Surface roughness comparison of samples treated in different ChCl –urea melts in
presence of SA or PS.
3000
2500
2000
1500
1000
500
0
1-4 1-2 1-1
Ra, nm
ChCl-Urea
Front Back Classical EP Raw Nb
Figure 5.27: Roughness dependence from ChCl – urea ratio in presence of Sulfamic acid.
Urea pauperization in the melt brings to decreasing of Nb dissolution reaction
efficiency. Instead of Nb dissolution on anode goes electrolyte decomposition.
If Nb dissolution depends of urea quantity, and concentration of regulators doesn’t
provide surface smoothing than becomes understandable that depassivation of Nb provides
only overvoltage and regulators bring only uniform current distribution. Urea provides
72. 72 EXPERIMENTAL PART
dissolving and ChCl serves like melt creator, in another worlds component which generate
matrix melt with urea. Also possible that – OH group of ChCl take part on cathode reaction
but less than protons from urea because of their bigger mobility.
There is a reason to check how PS and SA can work together. SA can be used like
usually as a current distribution regulator and particularly like regulator particularly like
depassivating agent.
5.2.5 Influence of additional NbCl5
Understanding what is necessary for preparing right solution needed for making
technology more simple and cheaper. Was tried to put additional NbCl5 in order to skip losing
time for solution preparing.
i=0,3 A/cm2 with overvoltage 65V. Galvanostate mode. t = 5 min
Sample 1 Sample 2 Sample 3 Sample 8 Sample 9
Electrolyte 1ChCl+4Urea, 10 min dissolving Nb.
After 30g/L SA added NbCl5
1ChCl+4Urea+30g/L
SA. Cool down to room
temperature.
3 NbCl5
5+), g/L 0 0,33 0,65 0,3 0,3
C(Nbadditional
Δm, g 0,509 0,536 0,522 - -
Ra(front), um 632±137 245±45 597±198 - 578±161
Ra(back), um 271±47 572±121 1206±410 - 322±218
Table 5.10: Experimental data of samples treated in1-4 ChCl –urea melt in presence of
additional NbCl5.
Adding NbCl5 brought to pitting from both sides of samples. Appearance of samples
looks more brightening and shining.
Temperature is increasing faster in the same range of potentials.
Samples 1, 2, 3 were electropolished on solution which was prepared from 1 part ChCl
and 4 parts Urea. After melting in solution was dissolved NbCl5 in temperature 120°C.
Adding of Nb salt was accompanied by gazing and slogging. Full dissolving took more than
30min. After full dissolving of salt was added SA.
Samples 8, 9 were electropolished in solution prepared in order:
1. Melting ChCl and Urea
2. Cooling down to 40°C adding NbCl5. Slow heating to 120°C.
3. After full salt dissolving added SA.
73. Two electrodes system 73
ChCl – Urea melt sediment
NbCl5
Figure 5.28: dissolving of NbCl5 in 1-4 ChCl – urea melt.
Summary: Adding of NbCl5 in solution doesn’t give a possibility to jump over
preliminary electrochemical dissolving of Nb and brings to pitting and increasing of
brightness. On a Figure 5.29 are shown roughness results obtained from samples which
were electropolished with additional NbCl5.
74. 74 EXPERIMENTAL PART
1800
1600
1400
1200
1000
800
600
400
200
Figure 5.29: Roughness of samples treated in presence of additional NbCl5.
Figure 5.30: Samples treated in presence of additional NbCl5.
0
0.0 0.2 0.4 0.6
Ra, nm
C(Nbadditional
5+), g/l
Front Back Sample 9 front
Sample 9 back Classical EP Raw Nb
75. Two electrodes system 75
5.2.6 Concurrently using PS and SA
Notwithstanding Sulfamic acid and ammonium persulfate have positive influence on
Nb EP process using them separately is not enough. SA provides current distribution evenness
which means uniform surface dissolving. PS allows to avoid overvoltage and to decrease
working current density. This factors have strong influence on solution self heating during
treatment.
Determining SA and PS best concentrations was done through the comparison of
samples roughness changing SA concentration at PS concentration 0, 2.5 and 5g/l.
Solution preparing was done as usually, first was added PS and after color stabilizing
was added SA. Was used automatic control potentiodynamic mode. Treatment time - 5 min.
5.2.6.1 C(PS) = 2,5g/L
3000
2500
2000
1500
1000
500
0
0.0 10.0 20.0 30.0 40.0
Ra, nm
Figure 5.31: Roughness of samples dependence from Sulfamic acid concentration in 1-4 ChCl
– urea melt at 2,5g/l ammonium persulfate concentration.
According to the Figure 5.31 with increasing SA concentration roughness of treated
samples is falling down and has the best value near 30 g/l.
C(SA), g/l
Front Back Classical EP Raw Nb
76. 76 EXPERIMENTAL PART
5.2.6.2 C(PS) = 5g/L
4500
4000
3500
3000
2500
2000
1500
1000
500
0
0.0 5.0 10.0 15.0 20.0 25.0
Ra, nm
Figure 5.32: Roughness of samples dependence from Sulfamic acid concentration in 1-4 ChCl
– urea melt at 5g/l ammonium persulfate concentration.
According to the Figure 5.32 with increasing SA concentration roughness of treated
samples is falling down and has the best value near 30 g/l.
C(SA), g/l
Front Back Classical EP Raw Nb
77. Two electrodes system 77
5.2.6.3 Summary - comparison between different composition of SA and PS used
concurrently.
1800
1600
1400
1200
1000
800
600
400
200
Figure 5.33: Roughness of samples dependence from ammonium persulfate concentrations in
1-4 ChCl – urea melt in Sulfamic acid presence.
According to Figure 5.33 is understandable that with increasing of PS concentration
roughness is increasing and has reasonable value at PS concentration 2,5g/l.
In conclusion to tests which were done with two electrodes system is offered best
solution with the next recipe:
Choline chloride - urea ratio 1-4
Sulfamic acid, g/l 30
Ammonium persulfate, g/l 2,5
t, °C 120
i range, A/cm2 0,33
Potential range, V
(Using automatic control software)
20-30
0
0 2.5 5
Ra, nm
C(PS), g/l
Front Back Classical EP Raw Nb
78. 7
an
8
dif
(lik
gro
ad
du
ou
Du
ga
5.3 A
In this
Application
s chapter wi
on of 1-4 Ch
nd applicatio
34: 6GHz ca
Figure 5.3
fficulties. H
ke the mos
oups).
cavities
wed system
melt with 30
avity section
High activity
st probable
Molec
cules H2 can
nd reduction
me.
designed EP
cathode. Fo
umping ele
aluate from
dsorption an
uring this tim
Was d
ut from the c
uring the pu
as which eva
n to 6GHz
ill be review
hCl – urea m
n.
y formation
e cathode r
n oxidize o
n there is n
P system(Fig
or this reaso
ctrolyte goe
cathode rea
for electrop
0g/l Sulfam
dist
ano
cav
nea
part
perf
EP
tem
insi
to
whi
poli
cav
n of cathode
reaction in
on anode on
no electrica
gure 5.35) w
on cathode w
es through
action.
EXPERIME
polishing in
mic acid for E
er to obta
he cathode
unately it is
part will b
ell part. To
ded cathode
ried to wo
horizontal
content res
ising, after
ity was mo
n of electr
mass. In tha
oxidizing.
ertical EP w
relative su
s to saturatio
which inc
In ord
tribution, th
ode. Unfortu
vity. Cutoff
arer than ce
tially shield
Was tr
formances:
didn’t give
mperature ri
ide the cavi
degradation
ite viscous m
ishing but o
With ve
vities with
e gas brings
electrolyte
n viscous fi
al field on a
ENTAL PAR
n ionic liquid
EP 6GHz ca
ain a favor
e need to
s not possib
be always in
o avoid thi
was used.
ork in two
and vertica
sults becaus
r 1 minute
re 190°C w
rolyte and
at places wa
RT
ds developi
avities.
rable curre
be far fro
ble inside t
n a few tim
s situation,
ing
ent
om
the
mes
, a
o geometric
al. Horizon
se of very fa
e temperatu
which broug
to formati
as done note
were electro
uccess but
on of electr
cludes –OH
film surface
anode surfa
where electr
was made o
the holes in
cal
ntal
fast
ure
ght
on
e a
opolished fe
there is al
rolyte with H
H and –NH
e. Time betw
ace which i
rolyte come
of tube 8mm
nside the tu
ew
lso
H2
H2
ween bubbl
is passivati
es from flan
m in diamet
ube and tak
les
ng
nges and go
er with hole
kes with its
oes
es.
elf
79. Application to 6GHz cavities 79
a) b)
Figure 5.35: Different cathode performance
a – full holled cothode; b – center holled cathode.
In the beginning was used configuration a (Figure 5.35). Cutoff part of the cavities
which were electropolished in this way had a good view(Figure 5.36), but from cell part
removing of material is not enough(Figure 5.37). Was decided to cover with Teflon cathode
across cutoff part of the cavity(Figure 5.35 configuration b). Cell part was electropolished
good(Figure 5.39) but opposite effect appeared on a cutoff part(Figure 5.38 ).
80. 80 EXPERIMENTAL PART
Figure 5.36: Cutoff part of cavity electropolished in 1-4 ChCl – urea melt with 30 g/l SA with
configuration a.
Figure 5.37: Cell part of cavity electropolished in 1-4 ChCl – urea melt with 30 g/l SA with
configuration a.
81. Application to 6GHz cavities 81
Figure 5.38: Cutoff part of cavity electropolished in 1-4 ChCl – urea melt with 30 g/l SA with
configuration b.
Figure 5.39: Cell part of cavity electropolished in 1-4 ChCl – urea melt with 30 g/l SA with
configuration b.
82. 82 RESULTS
6 Results
The classical electropolishing of Nb is a very well studied process. It is enough old
and very dangerous but it does not have an alternative. In this work it has been shown that
there are an the alternative methods which could be used instead of classical EP. This work is
the continuation of previous works and publications which were done in Superconductivity
Laboratory at LNL INFN.
First, were performed tests dedicated to matrix solution research, looking for
limitations, Nb dissolving mechanism understanding. After was a search for a regulators
which can provide equal current distribution on both sides of the sample using only one
counter electrode. Success was not in delay, it was found that Sulfamic acid can provide
uniform current distribution. Unfortunately there is the side of the medal. In order to break a
strong oxide film on Nb was used high overvoltage which brings huge(for water solutions)
current density. The behavior of current and potentials on the electrochemical cell provides
enormous heating of solution. It is possible to avoid this problem using SA and PS
concurrently. Then current density and working potential decrease. Also there is no necessity
of overvoltage in the beginning of the process. All recipes which gave useful results for
conclusion of work are reported in Table 6.1
ChCl
-
Urea
ratio
Regulator C, g/l Mode
Electrical
tension,
V
Current
density,
A/cm2
Roughness
(front),
nm
Roughness
Back), nm Note
1-1
Sulfamic acid 30 Manual 30…60 0,3 1242±23 779±10 No polishing
Ammonium
persulfate 10 Manual 20…40 - - No polishing
1-2
Sulfamic acid 40 Manual 30…60 0,3 1774±87 346±80 No polishing
Ammonium
persulfate 10 Autom. 20…40 1118±36 537±85 No polishing
1-4
Sulfamic acid 30 Autom. 30…60 0,3 274±26 241±41 Best
Ammonium
sulfate 40 Manual 30…60 0,3 631±134 456±78 Good
Ammonium
sulfamate 40 Manual 30…60 0,3 262±62 259±73 Good
Ammonium
persulfate 10 Autom. 20…40 752±138 662±232 Pitting
Sulfamic acid +
Ammonium
30 +
2,5 Autom. 20…40 438±25 441±94 Good
persulfate
Table 6.1: Principal recipes and their characteristics.