High Power Rf Input Couplers and Test Stand for the Berlinpro Project

The bERLinPro project [1], under construction at HZB, is a 100 mA, 50 MeV superconducting RF (SRF) energy recovery linac (ERL) being built to study the accelerator technology and physics of operating a high current SRF ERL. For this high current operation, coaxial RF power couplers capable of handling 115 kW of power (per coupler, dual couplers per cavity), continuous wave (cw) at 1.3 GHz are required for both the SRF photo injector and booster cavities. In order to sustain this power level a coupler has been designed based on the high power coupler currently in use at the KEK-cERL. Two key changes that were made to the coupler were the modification of the coupler tip, termed a golf-tee, as well as increased cooling of the inner conductor. This former modification is incorporated so as to achieve the desired coupling, Qext ~10, with minimal coupler penetration into the beam pipe. Herein, we discuss the RF design and properties of the high-power coaxial coupler for the photo injector as well as booster cavities of bERLinPro, along with the design of the test stand for conditioning a pair of couplers.