Overview of RF system for C-ADS injector Ⅱ radio frequency quadrupole

The RF system is a key part of the high intensity RFQ (Radio Frequency Quadrupole) accelerator in the project of Chinese Accelerator Driven System (C-ADS), which provides and transfers power for a quadrilateral four-vane resonator with two coupling ports. A special scheme was considered for accelerating 10 mA proton beam since the beginning of RFQ design. In this paper, the strategy for RF system, which is very important for demand of CW (continuous wave) operating mode, is considered; performance of the elements including an RF amplifier, couplers and a transmission system will be calculated and analyzed carefully to ensure they can operate reliably and safely. A test with 10 mA CW proton beam was carried out in 2015 to verify the design and configuration. Specially, a new kind of coupler with bowl-shaped ceramic window and a novel tuning method without circulator during beam commissioning are presented in detail, and the specific two-port configuration is deduced for accelerator operation firstly.