Martinet - Commissioning of a TE011 cavity for surface resistance measurement by calorimetric method
Commissioning of a TE011 cavity for surface resistance measurement by calorimetric method G. Martinet , M. Fouaidy, N. Hammoudi, S. Blivet, M. Labaste <ul><li>Motivations </li></ul><ul><li>Principle of the method </li></ul><ul><li>First test of the TE011 cavity at IPN </li></ul><ul><li>Status and schedule </li></ul>
Motivations <ul><li>Improve accuracy, sensitivity and reliability of Rs Measurement </li></ul><ul><li>Investigate Rs(T) in the temperature range 1.8-4.2K </li></ul><ul><li>Improve the sensitivity at 4.2K compared to RF method </li></ul><ul><li>Study spatial Rs distribution on the sample </li></ul><ul><li>Progress in the understanding of SRF properties and deposition process for thin films </li></ul>
Principle of the method For radius r>40mm P STAT =P RF T STAT = T RF Determination of R S coefficients (a, b, c) by least square method R=0 Rcav=55 Rseal=58 q HF Nb Cavity RF part LHe Thermometric part q STAT Vacuum Heater
Advantages and limitations of calorimetric method <ul><li>Better accuracy compared to RF method </li></ul><ul><li>Direct measurement method of dissipated power on the sample </li></ul><ul><li>No perturbations from extra losses </li></ul><ul><li>Measurements at 3.88 and 5.19 GHz </li></ul>T=1.7K T=4.2K Field Limitations For Bs<5mT: thermal instabilities due to switching from natural convection to nucleate boiling (Not hard limit!) For Bs>15mT: power limitation due to dissipations in the cylindrical part of the cavity (bulk Nb)
Expected performances With a detectable heating of 0.1 mK, the expected sensitivity should correspond to the following tables <ul><li>Limitation for maximum field reachable : </li></ul><ul><li>For high quality thin films and @T=1.8K the limitation should be the quench of the niobium cavity. </li></ul><ul><li>In other cases, it is depending of RF power dissipated on the sample, the critical field dependence with temperature and the cooling of the sample </li></ul>1 40 45 20 75 5 Sensitivity (n Ω ) @1.8K B s (mT) 5 15 10 10 45 5 Sensitivity (n Ω ) @4.2K B s (mT)
Thermometric system <ul><li>30 encapsulated carbon thermometers mounted in stainless steel chamber. Fixation with epoxy rod rounded by bronze/beryllium spring to guarantee thermal contact on the back side of the sample. </li></ul><ul><li>mapping of the surface resistance : 3 arms of 6 sensors for radial mapping at 120 degrees and 2 paired sensors between each one to access precisely to the RF power dissipated. </li></ul><ul><li>Possibility to localize defects (depending on their size and localization) </li></ul><ul><li>Liquid helium cooling all around the disc. Exchange surface increased by a 1 mm gab. </li></ul><ul><li>Arms support cooled down by 4 copper rods. </li></ul>
Reception of mechanical parts Thermometric chamber and niobium cavity has been received (august 2009) Dedicated system developed for chemical treatment and HPR process Design of a new nozzle to prevent electrical discharge
Conditioning for RF test Discs support for chemical treatment (“handmade” process) Cavity handling frame for chemical treatment and clean room assembly Preparation for HPR treatment of the sample and the cavity
RF results for the TE011 cavity Estimated Q0 value and dissipated power for theoretical R BCS (Nb RRR300) : @4.2K: 1.6 10 8 (1.1 10 8 ) and P cav =152W (62mT) @1.8K: 2.0 10 10 (1.4 10 10 ) and P cav =1.2W(62.mT) Huge residual resistance due to bad chemical treatment (80µm BCP, T ≈20°C)
Thermometric measurement Bpeak=52mT @ 4.2K reached! Good sensitivity (200mT/W for Nb@4.2K)
Schedule <ul><li>2 nd chemical treatment and improvement of HPR nozzle to measure ultimate performances of the cavity </li></ul><ul><li>Commissioning of movable coupler </li></ul><ul><li>Start characterisation of used niobium for current projects to improve preparation process and tools for analysis </li></ul><ul><li>Definition of thin films samples to characterize (films, substrates and process…) </li></ul>
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