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

Maebara, Sunao; Moriyama, Shinichi; Saigusa, Mikio*; Sugimoto, Masayoshi; Imai, Tsuyoshi; Takeuchi, Hiroshi

Fusion Engineering and Design, 75-79, p.823 - 827, 2005/11

https://doi.org/10.1016/j.fusengdes.2005.06.346

An RF-Input coupler with a multi-loop antenna using co-axial waveguides has been developed for the RFQ linac on IFMIF. In case of using a loop antenna, the loop antenna structure will affected phase difference and power balance in each cavity. A mock-up loop antenna using the pipe diameter of 10mm was fabricated, phase differences and power balances were measured by a low power test. It is found that it is necessary to shorten the installed depth up to 3 cm to make the phase differences and power balance small. But, from a withstanding voltage, it is difficult to couple multi-MW with the single coupler. The coupling with multi-loop antennas using two or four loops is better than one loop antenna from the point views of both withstanding voltage and power balance. The phase difference and power balance were also measured in both cases. A good average phase-difference of 179. and a good RF power balance within 8% error for each cavity were obtained. These results showed one of feasibility for an RF-Input coupler with a multi-loop antenna in the IFMIF 175 MHz RFQ.