Conceptual design of an RF-input coupler for the IFMIF RFQ linac

Maebara, Sunao; Moriyama, Shinichi; Fujii, Tsuneyuki; Okumura, Yoshikazu

In the preliminary design of prototype RFQ linac in the IFMIF/EVEA, a coupled cavity type 10.5 m-long RFQ is proposed to accelerate deuteron beam up to 5 MeV. The operation frequency of 175 MHz was selected to accelerate the large current of 125 mA in CW mode at the conceptual design phase. The driving RF power of 1.5 MW has to be injected to the RFQ cavity, and a stable CW injection without RF breakdown is essential to attain the required availability. It is designed to employ the input coupler system with multi-drive loop antennas connecting to co-axial waveguides. As the validation works, it is planned to measure the coupling factors of the loop antenna with varied insertion depths using RFQ test module and to test the RF power capability of 4- and 6-inch RF windows using a high-Q load circuit. The conceptual design of the RF-input coupler system for the IFMIF RFQ linac will be presented with the simulation results of coupling factor and multipactor phenomena.