High transmission mode purity coupling of gyrotron beam into EC transmission line

電子サイクロトロン伝送系へのジャイロトロンビームの高効率結合

小田 靖久; 梶原 健; 高橋 幸司; 春日井 敦; 坂本 慶司

Oda, Yasuhisa; Kajiwara, Ken; Takahashi, Koji; Kasugai, Atsushi; Sakamoto, Keishi

A long transmission line for ECH/CD system of ITER requires high transmission power efficiency. Good mode purity of the fundamental HE11 mode in the transmission line is necessary to minimize losses in the system. A coupling method of a 170 GHz gyrotron beam into a corrugated waveguide is proposed to achieve high HE mode purity in ECH/CD transmission line. A matching optical unit (MOU) with two phase correcting mirrors is used. Each mirror is mounted on a goniometer stage for angle control. The mode content in the waveguide is measured for several sets of mirror angles to maximize the mode purity. The mode content is deduced using RF field profiles radiated from the waveguide outlet. As a result, the beam coupling achieved greater than 90% of HE mode in the transmission power.