Etude du comportement de l'helium superfluide soumis a des flux de chaleur provoquant des changements de phase en paroi

SIGLEINIST T 75590 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Low Temperature Thermal Conductivity of Niobium and Materials for SRF Cavities

International audienceA test facility, allowing the test of 4 samples simultaneously during each run, was developed for measuring at low temperature (T= 1.5 K - 10 K) the thermal conductivity k(T) of niobium and other materials used for the fabrication of SRF cavities. The measurements are performed using steady-state axial heat flow method with a careful control of heat leaks to the surrounding. Several samples of different materials (industrial Nb sheets, Ti’) were either tested as received or/and subjected to various Heat Treatment (H.T) prior to the experiment then tested. The resulting experimental data are presented and compared to the experimental results previously reported by other groups. As expected, H.T @ 1200°C with Ti gettering improves the Nb RRR by a factor of 3 and consequently k(T). Finally, the correlation between the Niobium RRR and the thermal conductivity. at T=4.2 K is confirmed in good agreement with the Wiedemann-Franz law

Full Characterization at Low Temperature of Piezoelectric Actuators Used for SRF Cavities Active Tuning

In the frame of the CARE project activities, supported by EU, IPN Orsay participate to the development of a fast cold tuning system for SRF cavities operating at a temperature T=2 K. The study is aimed at full characterization of piezoelectric actuators at low temperature. A new experimental facility was developed for testing various prototypes piezoelectric actuators and successfully operated for T in the range 1.8 K-300 K. Different parameters were investigated as function of T: piezoelectric actuator displacement vs. applied voltage V, capacitance vs. T, dielectric and thermal properties vs. T and finally heating DT due to dielectric losses vs. modulating voltage Vmod and frequency. We observed a decrease of the Full Range Displacement (FRD or DX) of the actuator from ~40μm @ 300K down to 1.8μm-3μm @ 1.8K, depending on both material and fabrication process of the piezostacks. Besides, both material and fabrication process have a strong influence on the shape of the characteristics DX vs. T dependence. Moreover, the variations of losses tangent with T show a maximum at T in the range 30 K-120 K. Finally a dedicated facility located at CERI (Orléans, France) for radiation hardness tests of actuators with fast neutrons at T=4.2 K was developed and the first beam tests results are summarized

Recent Results of High Temperature Vacuum Heat Treatment Program of SRF Resonators at IJCLab

International audienceIn the framework of ESS, a vacuum furnace dedicated to High Temperature Heat Treatment under Vacuum (VH2T2) of SRF bulk niobium (Nb) cavities was developed and commissioned in May 2016. This furnace is mainly used for the reduction of interstitial hydrogen in niobium. VH2T2 is an effective process for curing SRF cavities from the so-called Q0-deases phenomenon, which is due to Nb hydrid formation on the RF surface during the cool down of the resonator to cryogenic temperatures. IJCLab VH2T2 process is done at 650 °C during 10h00. The main differences between IJCLab recipe and the standard VH2T2 (SVH2T2) are 2 folds: 1) SVH2T2 is performed at 800 °C during 3h00, 2) IJCLab recipe is applied to spoke resonators equipped with Ti LHe tank. This process, will be applied to the whole series (26 cavities) of ESS 352 MHz Double-Spoke resonators. More than 28 cavities of various type (ESS Double-Spoke resonators, MYRRHA single spoke, ESS elliptical medium and high β cavities) were successfully heat treated according to our recipe and the last results are reported. Moreover, since 2 years we have launched the R&D program HELOISE with the financial support of IN2P3/CNRS. HELOISE is dedicated to Heat Treatment of SRF niobium cavities: it includes Low Temperature Baking, VH2T2, Nitrogen Infusion and Nitrogen Doping processes. HELOISE main objectives are: 1) understand the complex mechanisms of the physical phenomena involved in heat treatment processes, 2) investigate the effect of the parameters impacting the process, 3) develop and master, at large scale and with good reliability, heat treatment processes in order to produce low RF losses and high gradient SRF bulk niobium cavities. Finally, we will focus on the first experimental data on Nitrogen Infusion we obtained: the corresponding results are reported and discussed

Commissioning of Vacuum Furnace and First Successful Heat Treatment of SRF Bulk Nb Cavities at IPN Orsay

International audienceA new vacuum furnace dedicated to high temperature heat treatment under vacuum (VH2T2) of superconducting radio frequency (SRF) bulk Nb cavities was developed, and operated. This furnace will be used for interstitial hydrogen removal (10h00 @ 650 degrees C) of similar to 26 spoke 352 MHz ESS cavities. We commissioned the furnace in May 2016: all the measured parameters of the intrinsic performances (i.e., residual pressure, thermal performance) are better than the specified values. Prior to applying VH2T2 to SRF cavities various qualification tests were performed on several samples: RRR, SIMS analysis, mechanical, and thermal properties at cryogenic temperature (as received samples versus VH2T2 samples). After the successful qualification, we performed VH2T2 at 650 degrees C on various bulk Nb SRF cavities (i.e., 1.3 GHz elliptical resonators and 352 MHz spoke resonators). All these heat treatments were successful. In this paper, we will report about: 1) furnace commissioning and qualification tests on samples, 2) RF tests of VH2T2 cavities

Status of High Temperature Vacuum Heat Treatment Program at IPN Orsay

International audienceIn the framework of ESS, a vacuum furnace dedicated to High Temperature Heat Treatment under Vacuum (VH2T2) of SRF bulk Nb cavities was developed and commissioned in May 2016. This furnace is currently used for interstitial hydrogen removal (10h00 @ 650 °C) of two type of cavities: 1) the whole series of 26 ESS 352 MHz spoke resonators equipped with their Ti LHe tank well, 2) some prototypes of ESS high beta and medium beta cavities. Up to know IPN Orsay VH2T2 (10h00 @ 650 °C) was successfully applied to more than 16 cavities. In this paper we will first report about these VH2T2 tests. Finally, we have just started testing nitrogen infusion and nitrogen doping processes on samples and 1.3 GHz cavities: the preliminary results will be discussed