The calculation of transverse kick by the input coupler of superconducting cavity for ERL main linac

Energy Recovery Linac (ERL) for future light source has been developed by KEK, JAEA, ISSP and other institutes in Japan. An input coupler must feed high power, which is estimated about 20 kW for 20 MV/m ERL operation, into the main linac superconducting cavities. Because the input coupler induced an asymmetric electromagnetic field in the cavity, accelerating TM010 mode produce a transverse kick similar to higher order modes. Using CST Microwave-Studio (MW-Studio), we calculated the transverse kick of accelerating mode induced by the input coupler. In case of the 'on crest' acceleration, the transverse kick by the transverse electric field and magnetic field are small as compared with the accelerating voltage. We also calculated the dependence with various inserted position of the coupler. In this paper, we will report the calculation of transverse kick and an arrangement of cavities to reduce the transverse kick. (author)