RRR of Copper Coating and Low Temperature Electrical Resistivity of Material for TTF Couplers

In the framework of the R&D program on the TTF III main RF coupler, IPN Orsay developed in close collaboration with LAL institute, a dedicated facility for the electrical characterization of different materials at low temperature. This apparatus was used for measuring the electrical resistivity versus temperature (4.2 K- 300K) of various samples produced in the industry. These tests were performed in order to compare the RRR of the samples, qualify and find the optimum parameters for the coating process. Seven flat samples were tested in a saturated liquid helium bath under ~1013 mbar pressure: measurements were performed on bare 316L samples, nickel coated 316L samples, and copper coated 316L samples with a nickel under layer. We investigated, in particular, the effect of vacuum annealing at 400°C on the RRR of the copper coating. Our experimental data are compared to previous measurements reported by other groups, and theoretical results (e.g. Gruneisen-Bloch equation) and a good agreement was found. Finally, the tested samples fulfil the TTF III coupler design parameters requirements in terms of heat loads to the refrigerator at 2 K, 4 K and 70 K

Electromechanical characterization of piezoelectric actuators subjected to a variable preloading force at cryogenic temperature

A dedicated apparatus was designed and constructed for studying the electromechanical behavior of prototype piezoelectric actuators subjected to a variable preloading force at cryogenic temperatures. This device was successfully used for testing a piezoelectric actuator of PICMA type from PI™, for T in the range 2 K-300 K. The dielectric properties as well as dynamic properties were measured including the actuator characteristics when used as force sensor. The corresponding data are reported and discussed

Development of a TE011 Cavity for Thin-Films Study

Bulk niobium cavities have almost reached their maximum performances. Maximum accelerating gradient field is above 35-40 MV/m for a multi-cells cavity at 1.8 Kelvin and it achieves 25-30 MV/m with high reliability. The question of increasing the accelerating gradient in a significant way is running regarding the huge amount of units required for new projects (16000 units for ILC). A promising solution is to use thin films of new materials deposited on copper or niobium. In order to investigate the behaviour of these materials for the accelerating cavities, we have developed a dedicated setup based on thermometric method and a TE011 cavity. We present here the design study of the setup and the expected sensitivity of the method for the surface measurement of materials properties under RF fields