Study of sub-terahertz high power gyrotron for ECH&CD system of DEMO

DEMO炉に向けた電子サイクロトロン加熱電流駆動システムのためのサブテラヘルツ帯大電力ジャイロトロンの研究

坂本 慶司; 假家 強*; 小田 靖久; 南 龍太郎*; 池田 亮介; 梶原 健; 小林 貴之; 高橋 幸司; 森山 伸一; 今井 剛*

Sakamoto, Keishi; Kariya, Tsuyoshi*; Oda, Yasuhisa; Minami, Ryutaro*; Ikeda, Ryosuke; Kajiwara, Ken; Kobayashi, Takayuki; Takahashi, Koji; Moriyama, Shinichi; Imai, Tsuyoshi*

For the Electron cyclotron resonance heating and current drive (ECH&CD) system on fusion DEMO reactor, the high power mm-wave of 200 GHz 300 GHz is expected. To increase the gyrotron frequency, extremely high-order oscillation mode should be adopted to suppress the Ohmic loss on the resonator wall less than ~20 MW/m. Here, we designed and fabricated a 300 GHz gyrotron of TE32,18 mode oscillation and started a short pulse experiment to investigate the oscillation characteristics of the high order mode at ~300 GHz. As a preliminary result, we demonstrated the power generation of ~0.5 MW at ~300 GHz oscillation at the oscillation mode of TE32,18, and other modes. A height of the test gyrotron is ~2 m. The electron gun is diode type magnetron injection gun (MIG), to maximize the diameter of an electron emitter (d = 74 mm). The resonator is a conventional open cavity. The diameter is 31.6 mm, which corresponds to the 300 GHz oscillation with TE32,18 mode. This mode is capable of 0.5 MW/300 GHz at CW operation. The distance from the emitter to the resonator is ~520 mm. The oscillation power is transmitted by the collector as a waveguide, and outputted as the oscillation mode through the sapphire window of 102 mm in diameter. A super-conducting magnet (SCM) is a 13 T liquid-He-free-magnet, which has a room temperature bore diameter of 110 mm. A dummy load is put on the top of the gyrotron to absorb and measure the output power. In the experiment, we demonstrated the power generation of ~0.5 MW at ~300 GHz oscillation at the TE32,12 mode. The applied beam voltage is 80 kV, and the beam current is 36.8 A. Pulse duration is ~2 msec. A MIG field is optimized to oscillate the target mode. The power peak was around 12.0 T, which corresponds to the TE32,18 mode. By decreasing the magnetic field to ~11.73 T, lower adjacent mode TE31,18 appeared. Detailed studies of the mode competition, etc., will be carried out.