Measurement of RF transmission mode in ITER relevant EC H&CD transmission line

小田 靖久; 梶原 健; 高橋 幸司; 春日井 敦; Shapiro, M.*; Temkin, R.*; 坂本 慶司

Journal of Infrared, Millimeter, and Terahertz Waves, 31(8), p.949 - 957, 2010/08

In this report, the preliminary results of the mode measurement in the ITER relevant 40 m distance transmission test line composed from 63.5 mm corrugated waveguides and miter bends are presented. The field patterns were measured by taking temperature profiles on a paper screen placed in front of the waveguide end using an infrared imaging camera. The complex electric field at the waveguide end was retrieved from the measured temperature profiles. As a result, the transmission power included 87% of HE mode and 6% of LP odd (HE+TE) mode and small ratios of other modes and the mode content ratio had small dependence on length of the transmission line. This was because LP mode which was generated at the initial coupling propagated through the transmission line. Hence the initial coupling of gyrotron beam into the transmission line is important to improve mode purity.