Study of thermal interaction between a 150 KW CW POWER coupler and a superconducting 704 MHZ elliptical cavity

The power coupler needed for β=0.65 SRF elliptical cavities dedicated to the driver of XADS (eXperimental Accelerator Driven System) should transmit a CW RF power of 150 kW to a 10 mA proton beam. The estimated average values of the RF losses in the coupler are 130 W (respectively 46 W) for the inner (respectively outer) conductor in SW mode. Due to such high values of RF losses, it is necessary to very carefully design and optimize the cooling circuits of the coupler in order to efficiently remove the generated heat and to reduce the thermal load to the cavity operating at T=2 K. An experiment simulating the thermal interaction between the power coupler and a 700 MHz SRF five cells cavity was performed in the CRYHOLAB test facility in order to determine the critical heat load that can be sustained by the cavity without degradation of RF performance. Experimental data are compared to numerical simulation results obtained with the Finite Element code COSMOS/M. These data allow us also to perform in-situ measurements of thermal parameters needed in the thermal model of the coupler (thermal conductivity, thermal contact resistance) and they were used to validate numerical simulations