NEW HOM COUPLER DESIGN FOR ERL INJECTOR AT KEK

The development of superconducting cavities and cavity package for ILC and ERL project is under way at STF (Superconducting RF Test Facility) in KEK. The TESLA-style coaxial HOM couplers have a problem at CW operation, which it is pick-up probe and inner conductor heating of HOM coupler. The pick-up probe heating was observed at vertical tests. The probe heating study for CW operation (changing pick-up probe geometry and probe gap) tried at vertical tests by using the KEK STF Baseline 1.3 GHz 9-cell superconducting cavity, and simulated by using HFSS code ver9.1 for estimate the relation of the limit E-field of probe heating and the probe surface current. The design of proto-type coaxial HOM couplers of CW operation for ERL-injector at KEK was tried based on this information. The probe heating is generated due to the probe surface current by the RF load of accelerating mode. Therefore, as one method, it can be controlled if the RF load of accelerating mode is reduced by putting the high pass filter between the coupling loop and the notch filter. In addition, the target beam current of ERL is about 100mA, therefore, we were considered that the cooling of inner conductor of HOM coupler by liquid He. It is necessary to be expected the heating of inner conductor by RF load of accelerating mode and HOM power of excited in the beam. The design was held based on these. In this report, a design of HOM coupler for ERLinjector at KEK is presented.