Input coupler for ERL injector cavities

A conceptual design of the input coupler for superconducting injector cavities of Cornell/JLab ERL project is presented. The injector cavities are two-cell structures operating at 1300 MHz in CW mode. The coupler has a symmetric design to accommodate requirements for small transverse kick, high RF power delivery to the cavity, and high input coupling value. Therefore it consists of two identical antenna type couplers symmetrically attached to a beam pipe of the cavity. Each coupler delivers 50 kW of CW RF power to the beam. The coupler has a variable coupling. Q/sub ext/ should be varied from 4.6 /spl times/ 10/sup 4/ to 4.1 /spl times/ 10/sup 5/. The symmetric design of the coupler dramatically reduces the transverse kick, a critical requirement for the ERL project. Estimates of the influence of coupler induced fields on beam dynamics are given.