This document summarizes the findings of nanostructure analysis of the penetration depth in niobium cavities conducted by Yulia Trenikhina. Trenikhina used transmission electron microscopy to examine cutouts from cavities treated with electropolishing only and electropolishing followed by a 120C bake. The analysis revealed precipitation of niobium hydrides in the electropolished cavity but not in the baked cavity at cryogenic temperatures. This suggests that the formation or size of niobium hydrides in the near-surface region is responsible for the high field Q slope phenomenon, as the baked cavity did not exhibit this problem. Further studies of cavities treated with different recipes also showed niobium hyd
Lobanov - Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgradethinfilmsworkshop
http://www.surfacetreatments.it/thinfilms
Nb sputtered 150 MHz quarter-wave resonators for ANU LINAC Upgrade (Nikolai Lobanov - 20')
Speaker: Nikolai Lobanov - The Australian National University | Duration: 20 min.
http://www.surfacetreatments.it/thinfilms
Cylindrical Post-Magnetron sputtering for High Rate Niobium deposition (Cristian Pira - 15')
Speaker: Cristian Pira - INFN-LNL | Duration: 15 min.
Abstract
The use of Nb/Cu cavity at CERN for the LEP and at the INFN-LNL for Alpi Linac has demonstrated the possibility to use this technology for particles accelerators to substitute the more expensive technology of niobium bulk cavity. The limit of the Nb/Cu cavity is the Q-slope, which decreases the Q factor at high accelerating fields. The accelerators community supposes that it’s possible to eliminate, or to decrease, the problem of Q-slope with high pure films of sputtered niobium. One way to obtain pure films is to decrease the number of impurities enclosed in the growing film.
It’s possible to reduce the number of impurities when the sputtering rate process increases.
We study the possibility to enhance the plasma density in order to increase the sputtering rate and then reduce the impurities in the niobium sputtered film and finally obtain high pure films.
In order to enhance the plasma density we sputter the niobium target with high currents to heat it and get to thermoionic emission. This sputtering method is called high rate sputtering.
First results of Niobium coatings will be presented.
Lobanov - Nb-sputtered 150 MHz Quarter-wave Resonators for ANU Linac Upgradethinfilmsworkshop
http://www.surfacetreatments.it/thinfilms
Nb sputtered 150 MHz quarter-wave resonators for ANU LINAC Upgrade (Nikolai Lobanov - 20')
Speaker: Nikolai Lobanov - The Australian National University | Duration: 20 min.
http://www.surfacetreatments.it/thinfilms
Cylindrical Post-Magnetron sputtering for High Rate Niobium deposition (Cristian Pira - 15')
Speaker: Cristian Pira - INFN-LNL | Duration: 15 min.
Abstract
The use of Nb/Cu cavity at CERN for the LEP and at the INFN-LNL for Alpi Linac has demonstrated the possibility to use this technology for particles accelerators to substitute the more expensive technology of niobium bulk cavity. The limit of the Nb/Cu cavity is the Q-slope, which decreases the Q factor at high accelerating fields. The accelerators community supposes that it’s possible to eliminate, or to decrease, the problem of Q-slope with high pure films of sputtered niobium. One way to obtain pure films is to decrease the number of impurities enclosed in the growing film.
It’s possible to reduce the number of impurities when the sputtering rate process increases.
We study the possibility to enhance the plasma density in order to increase the sputtering rate and then reduce the impurities in the niobium sputtered film and finally obtain high pure films.
In order to enhance the plasma density we sputter the niobium target with high currents to heat it and get to thermoionic emission. This sputtering method is called high rate sputtering.
First results of Niobium coatings will be presented.
Práctica de laboratorio referente a las operaciones fundamentales de un laboratorio. Experimentos sobre la medición, peso, mezcla, disolución, filtración, evaporización, precipitación de sustancias. Cuestionario y conclusiones del trabajo.
Esperemos que este trabajo te sea de ayuda. Estudiantes de Ingeniería unidos unos a otros. Por favor, divulga el material si le es necesario a otro estudiante. Gracias.
Enzo palmieri experimental results on thermal boundary resistance for niobi...thinfilmsworkshop
Unless of a few eclectic scientists that have studied the problem of Kapitza resistance, a superconducting cavity is almost always seen as an adiabatic system of the electromagnetic fields interacting with a Niobium sheet cooled at 4,2K or at temperatures between 1,8K and 2 K. In this talk it will be shown that the real system to consider is that of Electromagnetic fields, Niobium and liquid Helium.
And liquid Helium is a component much more complex than an infinite heat exchanger at fixed temperature. Even at superfluid temperatures indeed, at the interface between Helium and the superfluid, it will be always a nanometric thick layer of normal helium and the thickness of this layer depends on the RF power.
Niobium sputtered cavities will be also examined under the point of view of thermal boundary Resistance, arriving to the conclusion that more advanced comprehension of SRF cannot prescind from a deep understanding of Cryogenics
Paul welander cryogenic rf characterization of sc materials at slac with cu...thinfilmsworkshop
A second-generation, X-band cryostat has been developed for the characterization of superconducting materials at low temperatures and high powers. The system utilizes two interchangeable hemisperhical cavities that can accommodate 50 mm-diameter samples on the flat surface. Both operate in a TE013-like mode where the magnetic field is strongest on the sample surface, which accounts for about 1/3 of the total cavity loss. The first cavity is a medium-Q copper one, and is utilized for measuring the sample’s critical temperature and magnetic quenching field. The second is a high-Q niobium-coated cavity that is employed for measuring surface resistance in the low-temperature, low-power limit. We will discuss cryostat design, measurement limits, and testing of samples grown both at SLAC and elsewhere.
Yulia trenikhina tem studies of niobium hydrides participants in supercondu...thinfilmsworkshop
Nanoscale near-surface investigation of cutouts from niobium cavities is the most direct way to understand the material features affecting the SRF performance. We will present temperature dependent TEM studies on cutouts from Q-disease free cavities prepared by EP, EP+120C baking, and N doping. We have found that several niobium hydride phases form upon cooldown to <100K in the penetration depth for EP and EP/120C cutouts with the difference in the density/size caused by 120C. No hydrides were found in the first few tens of nanometers of the N doped cutouts.These findings support the proposed involved of niobium nanohydrides in the high field Q slope, and the effect of N doping.
Daniel adrien franco lespinasse - status of magnetron sputtered qwrthinfilmsworkshop
The objective of this research is the deposition of a superconductive thin film onto copper Quarter Wave Resonator cavities that can be used in the HIE-ISOLDE facility at CERN. To do this, it was developed an innovative magnetron configuration source. Our experience has shown the efficiency of this particular configuration in order to deposit a uniform thin film, and also improve the superconductive properties of the niobium (Residual Resistance Ratio and Critical Temperature). This presentation presents the recent improvement of the niobium thin film properties and the procedure used to deposit and measure the first resonator at LNL of HIE-ISOLDE type.
Práctica de laboratorio referente a las operaciones fundamentales de un laboratorio. Experimentos sobre la medición, peso, mezcla, disolución, filtración, evaporización, precipitación de sustancias. Cuestionario y conclusiones del trabajo.
Esperemos que este trabajo te sea de ayuda. Estudiantes de Ingeniería unidos unos a otros. Por favor, divulga el material si le es necesario a otro estudiante. Gracias.
Enzo palmieri experimental results on thermal boundary resistance for niobi...thinfilmsworkshop
Unless of a few eclectic scientists that have studied the problem of Kapitza resistance, a superconducting cavity is almost always seen as an adiabatic system of the electromagnetic fields interacting with a Niobium sheet cooled at 4,2K or at temperatures between 1,8K and 2 K. In this talk it will be shown that the real system to consider is that of Electromagnetic fields, Niobium and liquid Helium.
And liquid Helium is a component much more complex than an infinite heat exchanger at fixed temperature. Even at superfluid temperatures indeed, at the interface between Helium and the superfluid, it will be always a nanometric thick layer of normal helium and the thickness of this layer depends on the RF power.
Niobium sputtered cavities will be also examined under the point of view of thermal boundary Resistance, arriving to the conclusion that more advanced comprehension of SRF cannot prescind from a deep understanding of Cryogenics
Paul welander cryogenic rf characterization of sc materials at slac with cu...thinfilmsworkshop
A second-generation, X-band cryostat has been developed for the characterization of superconducting materials at low temperatures and high powers. The system utilizes two interchangeable hemisperhical cavities that can accommodate 50 mm-diameter samples on the flat surface. Both operate in a TE013-like mode where the magnetic field is strongest on the sample surface, which accounts for about 1/3 of the total cavity loss. The first cavity is a medium-Q copper one, and is utilized for measuring the sample’s critical temperature and magnetic quenching field. The second is a high-Q niobium-coated cavity that is employed for measuring surface resistance in the low-temperature, low-power limit. We will discuss cryostat design, measurement limits, and testing of samples grown both at SLAC and elsewhere.
Yulia trenikhina tem studies of niobium hydrides participants in supercondu...thinfilmsworkshop
Nanoscale near-surface investigation of cutouts from niobium cavities is the most direct way to understand the material features affecting the SRF performance. We will present temperature dependent TEM studies on cutouts from Q-disease free cavities prepared by EP, EP+120C baking, and N doping. We have found that several niobium hydride phases form upon cooldown to <100K in the penetration depth for EP and EP/120C cutouts with the difference in the density/size caused by 120C. No hydrides were found in the first few tens of nanometers of the N doped cutouts.These findings support the proposed involved of niobium nanohydrides in the high field Q slope, and the effect of N doping.
Daniel adrien franco lespinasse - status of magnetron sputtered qwrthinfilmsworkshop
The objective of this research is the deposition of a superconductive thin film onto copper Quarter Wave Resonator cavities that can be used in the HIE-ISOLDE facility at CERN. To do this, it was developed an innovative magnetron configuration source. Our experience has shown the efficiency of this particular configuration in order to deposit a uniform thin film, and also improve the superconductive properties of the niobium (Residual Resistance Ratio and Critical Temperature). This presentation presents the recent improvement of the niobium thin film properties and the procedure used to deposit and measure the first resonator at LNL of HIE-ISOLDE type.
Anne marie valente-feliciano - multilayer approach to increase the performanc...thinfilmsworkshop
For the past three decades, bulk niobium has been the material of choice for SRF cavities applications. RF cavity performance is now approaching the theoretical limit for bulk niobium. For further improvement of RF cavity performance for future accelerator projects, Superconductor-Insulator-Superconductor (SIS) multilayer structures (as proposed by Alex Gurevich) present the theoretical prospect to reach RF performance beyond bulk Nb, using thinly layered higher-Tc superconductors with enhanced Hc1. Jefferson Lab (JLab) is pursuing this approach with the development of NbTiN and AlN based multilayer SIS structures via magnetron sputtering and High Power Impulse Magnetron Sputtering (HiPIMS). This contribution presents the characterization of NbTiN and insulator films and some RF measurements on NbTiN-based multilayer structures.
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.
Anne marie valente feliciano - nucleation of nb films on cu substratesthinfilmsworkshop
In the pursuit of niobium (Nb) films with similar performance with the commonly used bulk Nb surfaces for Superconducting RF (SRF) applications, significant progress has been made with the development of energetic condensation deposition techniques. The controlled incoming ion energy enables a number of processes such as desorption of adsorbed species, enhanced mobility of surface atoms and sub-implantation of impinging ions, thus producing improved film structures at lower process temperatures. All these along with the quality of the Cu substrate have an important influence on the nucleation and subsequent growth of the Nb film, creating a favorable template for growing the final surface exposed to SRF fields. This contribution shows how the structure and defect density thus electron mean free path (represented by residual resistance ratio values) of Nb films can be tailored on Cu substrates, by varying the ion energy and thermal energy provided to the substrate, favoring the hetero-epitaxial or the fiber growth mode.
Master Thesis Total Oxidation Over Cu Based Catalystsalbotamor
The evolution in the oxidation state of Cu and Ce in a benchmark catalyst is studied
under different conditions: temperature programmed reduction with propane and hydrogen,
and isothermal reduction with propane and hydrogen.
Analytical methods used involve operando X-ray absorption spectroscopy (XAS) in
transmission mode at the Cu K edge and Ce LIII edge, as well as online mass spectrometry
(MS) at the outlet of the reactor.
Magnetic Gold; Structure Dependent Ferromagnetism in Au4VDamon Jackson
A description of the ferromagnetic interactions found in crystallographic Au4V is investigated through high pressure (P<35 GPa) electrical resistivity measurements. The results suggest an intimate connection between crystallographic structure and ferromagnetism for this material.
1. Yulia Trenikhina
SRF 2015
Whistler, Canada
09/16/2015
Nanostructure of the penetration depth
in Nb cavities: debunking the myths
and new findings
2. Yulia Trenikhina SRF’15 Whistler, Canada2
16
EP + 120C ba
50 100 150
2
4
6
8
10
12
14
16
Electropolish
Angl
Sensornumber
50 100 150
109
1010
1011
FG
FGB
Q0
Bpeak
(mT)
(a)
(b)
(c)
(d)
HFQS elimination in FG
EP cavities after 120°C
bake
HFQS-producing treatments
High Field
Q-slope
HFQS recipes:
EP
EP+800C bake+BCP
EP+800C bake
EP
EP+120C
3. Yulia Trenikhina SRF’15 Whistler, Canada
Cavity diagnostics: EP vs. EP+120C baked
3
the peak surface mag-
orresponding excitation
cavities. The Q0ðBpeakÞ
the maps are shown in Fig. 1(b). Samples 2-EP and 6-BCP
had DTðBÞ curves of the shape similar to 1-EP, and that for
4-BCP would be expected to be the same. All mild baked
s on fine grain electropolished cavities before and after mild baking; (b) individual DTðBÞ for samples 1-EP and
tached to the outside cavity walls; three boards are removed for demonstration purposes; (d) single individual
EP and 120C bakedEP (not baked)
T-maps @ 28 MV/m
4. Yulia Trenikhina SRF’15 Whistler, Canada
EP vs. EP+120C baked: what is causing HFQS?
4
few monolayers of hydrocarbons
Nb2O5 2-5nm
NbOx x<2.5
Nb bulk
magnetic field
penetration
depth @2K
<100 nm
Near-surface layer of SRF cavity
after typical processing
What in the near-surface is causing different dissipation character?
5. Yulia Trenikhina SRF’15 Whistler, Canada
Hypothesis for the HFQS problem: what is the difference?
5
,&-$ *'<$ (.8'.,.%*')$ 1#'8)"$ &,$ ).3#$ .'$ )"#(#$ #';.-&'T
3#')(D$@&I#;#-B$-#%&32.'*).&'$*'=$20221#$'0%1#*).&'
).&'$ =.*8-*3$ ("&I'$ .'$ A.8D P4*6D$ !"
("&I($P$H"*(#(O
>FP
@*."2D" K.&2.03T@<=-&8#'$H"*(#$=.*8-*3$-#H&-)#=$2<$`*'%"#()#-$*'=$G.)-#$^FV_$4*6$*'=$5S hN$#/0.1.2-.03$H-#((0-#$*'=$H&)#')
"<=-.=#$H"*(#($2*(#=$&'$)"#$=*)*$&,$A-&33$*'=$#"'$^P9_$,&-$)"#$α *'=$α i β -#8.&'($*'=$`*'%"#()#-$*'=$G.)-#$^FV_$,&-$)"#$β i
Nb hydride
precipitation
Tool:
T-dependent TEM electron diffraction
phase characterization
Why to look at Nb-H system?
1. H concentration in near-surface
of cutouts > 10 at.%
2. ε, β are NOT superconducting
Difference in precipitation state of
Nb-H in the near-surface?
6. Yulia Trenikhina SRF’15 Whistler, Canada
Hypothesis: Nb hydrides and HFQS
6
• Normal conducting Nb hydrides are SC by proximity effect up to Hcritical = HFQS
onset (A. Romanenko et.al., Supercond. Sci. Technol. 26, 035003 (2013));
• Major role of vacancies and vacancy-hydrogen complexes in the 120C baking
effect (A. Romanenko et.al., Appl. Phys. Lett. 10, 232601 (2013)).
NbOx
Nb2O5
Nb
H
NbOx
Nb2O5
Nb
V-nH
complex
EP cavity 120˚C-baked EP cavity
Less/no NbHx precipitation!
~50 nm
7. Yulia Trenikhina SRF’15 Whistler, Canada7
30TEM Sample Preparation with FIB @ Ben Myers - 2009
L 0° Tilt
L Raise Omniprobe ~10 m
L Retract Pt GIS needle
L Send Omniprobe to Eucentric High
L Retract Omniprobe
FIB
FIB
J Shape: Rectangle
J Size: ~10 m (X) x ~2 m (Y)
J 5kV, ~46pA
J ~2-5min per side
FIB -
S
22TEM Sample Preparation with FIB ? Ben Myers - 2009
E Application: Pt e-Dep
E Shape: Rectangle
E 15 m (X) x 1.5 m (Y) x 200nm (Z)
E 2-5kV, >1.4nA
E-beam dep at
0° Tilt (SEM)
E-beam dep at
52° Tilt (SEM)
SEM
~10 μm
~3μm
SEM images during the FIB sample preparation
TEM sample preparation: focused ion beam
Cugrid
Pt protective layer
Courtesy of B. Meyer
8. Yulia Trenikhina SRF’15 Whistler, Canada
Nb near-surface at room T
8
[113] [011]
[-111]
EP and EP+120C baked at room T
SAD, NED, SEND: only Nb at room T
H in solid solution (α-phase)
[100]
Pt protective layer
Nb bulk
Nb oxide
200 nm
TEM: low mag overview
9. Yulia Trenikhina SRF’15 Whistler, Canada
Nb near-surface at cryogenic T
9
βε
ε+β
βε
ε β β
ε ε ε+β ε+β
ε ε ε
ε
ε
ε
ε
ε ε
ε
ε
ε+β
ε+β
εε+β β
_ _ _ _
EP at 94K EP+120C baked at 94K
Nb+ε(Nb4H3)
Nb+β(NbH)
Nb+ε,β
Nb hydrides precipitation
Nb
NO Nb hydrides precipitation
Nb
10. Yulia Trenikhina SRF’15 Whistler, Canada
Nb near-surface at cryogenic T continue
10
NED: Nb hydrides precipitation in all cutouts,
amount and/or size of Nb hydrides is different
EP at 94K EP+120C baked at 94K
Nb hydrides
Nb hydrides
12. Yulia Trenikhina SRF’15 Whistler, Canada
HFQS recipes:
EP
EP+800C bake+BCP
EP+800C bake
large size or large amount of
Nb hydrides at 94K
=
HFQS-free recipe:
EP+120C bake
Cause of HFQS
12
small/widely spread Nb
hydrides at 94K=
13. Yulia Trenikhina SRF’15 Whistler, Canada
Grain boundaries in EP and EP+120C baked
13
grain 1 grain 2
SEM image of GB
Pt layer
Nb2O
5
HRTEM image of GB
14. Yulia Trenikhina SRF’15 Whistler, Canada
EELS study of Nb oxides in EP and EP+120C baked cavities
14
120x10
3
100
80
60
40
20
0
counts,arb.units
395390385380375370365360355
energy loss, eV
region 1
region 2
region 3
region 4
Nb
Nb oxides
Pt layer
STEM Z-contrast image
Oxygen inward diffusion during the bake
EELS Nb M2,3 edge
EP+120C
EP
1
2
3
4
15. Yulia Trenikhina SRF’15 Whistler, Canada
Nb hydrides in N-doped cavity cutouts and samples
15
• Nb hydrides do precipitate in N
doped cavities and samples!
Most of the probed area is affected by
hydride precipitation in quench spot.
• Do Nb hydrides cause quench in N
doped cavities?
Cryogenic temperature structural
characterization of non-dissipating spot
is needed.
More about N doped
cavities in MOPB055
Quench Spot at 94K
baked with N @800C + 5 μm EP
?
16. Yulia Trenikhina SRF’15 Whistler, Canada
Conclusions
16
• Combination of T-dependent macro- and microscopic
characterization revealed precipitation of Nb hydrides in the state-
of-the-art SRF resonators for the 1st time;
• We showed that micro- and nanoscopic characterization gives a
valuable insight into mechanisms that governs the performance of
SC cavities;
• Routine use of micro- and nanoscopic characterization for the
development of new SC materials and treatments for the SRF
cavities.
17. Yulia Trenikhina SRF’15 Whistler, Canada
Microscopic characterization for new materials/treatments
17
We are working on: Nb3Sn coating of Nb cavities with Cornell
Nb3Sn coated Nb cavity: SEM/EDX on cavity cutouts
More about Nb3Sn in Sam Posen’s
posters TUPB048, TUPB049 and
Yulia’s poster TUPB056.
Thanks for your attention!