Development of an RF-input coupler with a multi-loop antenna for the RFQ linac in IFMIF project

Abstract An radio-frequency (RF)-input coupler with a multi-loop antenna using co-axial waveguides has been developed for the radio-frequency quadrupole (RFQ) linac on International Fusion Materials Irradiation Facility (IFMIF). In the case of using a multi-loop antenna, the antenna structure affects the phase difference and the power balance in each cavity. A mock-up loop antenna using a pipe diameter of 10 mm has been fabricated, and phase differences and power balances were measured by a low power test. It was found that the installed depth has to be shortened by 3 cm to make phase differences small. But, due to voltage limits, it is difficult to couple multi-MW using a single coupler. Coupling using two-loop or four-loop antenna is better than one-loop antenna. Phase differences and power balances were also measured in both cases. When a four-loop antenna was installed into the RFQ, a good average phase difference of 180° and a good RF power balance within 8% variation was obtained. The electric field profiles in the beam bore were also calculated by MW-Studio. It was found that distortion of electric field is negligible small in the case of using four-loop antenna. These results showed the feasibility of using as an RF-input coupler comprising a four-loop antenna in the IFMIF 175 MHz RFQ.

[1]  M. Saigusa,et al.  Low power test of RFQ mock-up modules at 175 MHz for IFMIF project , 2003, Proceedings of the 2003 Particle Accelerator Conference.

[2]  L. M. Young,et al.  Operations of the LEDA resonantly coupled RFQ , 2001, PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268).

[3]  Tatsuo Kondo,et al.  IFMIF, its facility concept and technology , 1998 .

[4]  M. J. Rennich,et al.  Conceptual design of the international fusion materials irradiation facility (IFMIF) , 1998 .

[5]  Lloyd M. Young,et al.  CW RFQ fabrication and engineering , 1998 .

[6]  Richard L. Sheffield,et al.  Low-Energy Demonstration Accelerator (LEDA) test results and plans , 2001, PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268).