High power input coupler development for BEPCII 500 MHz superconducting cavity

A high power input coupler for a 500 MHz superconducting cavity (SCC) of the upgrade project of Beijing Electron Positron Collider (BEPCII) has been developed in China. Several prototypes have been fabricated and tested successfully. A maximum of 420 kW continuous wave (CW) RF power in traveling wave (TW) mode was achieved in the high power test. The detailed design, fabrication and test of the coupler are described in this paper.