Development of fundamental power coupler for high current superconducting RF cavity

Brookhaven National Laboratory took a project of developing a 704 MHz five-cellsuperconducting RF cavity for high-current linacs, including Energy Recovery Linac (ERL)for planned electron-hadron collider eRHIC. The cavity will be fed by a high-power RFamplifier using a coaxial Fundamental Power Coupler (FPC), which delivers 20 kW of CW RFpower to the cavity. The design of FPC is one of the important aspects as one has to takeinto account the heat losses dissipated on the surface of the conductor by RF fields alongwith that of the static heat load. Using a simple simulation model we show the temperatureprofile and the heat load dissipated along the coupler length. To minimize the heat load onFPC near the cavity end, a thermal intercept is required at an appropriate location on theFPC. A 10 K intercept was chosen and its location optimized with our simulation code. Thehelium gas flow rate required for effective heat removal from the thermal intercept is alsodiscussed.