ITER用ミリ波源ジャイロトロンの現状と核融合炉に向けた展望

Present status of gyrotron development for ITER and prospect of advanced gyrotron for fusion reactor

春日井 敦; 高橋 幸司; 梶原 健; 小林 則幸; 坂本 慶司

Kasugai, Atsushi; Takahashi, Koji; Kajiwara, Ken; Kobayashi, Noriyuki; Sakamoto, Keishi

原子力機構では、高周波を用いたITER用プラズマ加熱装置ジャイロトロンの開発を進めている。これまでにITER用ジャイロトロンについて、50%の効率の達成,人工ダイヤモンド窓の開発,1MW級高周波の発振などを達成し、長パルス化研究を進めてきた。しかしジャイロトロン内部での発熱や長パルス時における発振出力の低下等により、総合効率は40%程度、出力時間は100秒程度に制限されてきた。そこでこれらの課題を克服するため、高周波回路,電子銃,制御方式の改良等を行った。その結果、出力0.6MW,総合効率46%,動作時間1時間(3600秒)の大電力定常動作の実証に成功した。動作時間1時間はITERで要求される燃焼時間400秒より十分長く、将来ITERで想定されるさまざまな運転モードにも対応できる動作時間である。さらに、長パルス動作時の発振特性を明らかにし、長パルス動作過程で電子ビームのピッチファクター,空胴磁場強度を制御することで、ジャイロトロンの運転領域を高効率領域まで引き上げる運転モードを新たに確立し、その結果、出力0.82MW,56%の高効率で600秒(10分)以上動作させることに成功した。

In Japan Atomic Energy Agency, the development of the 170 GHz gyrotron with the oscillation mode of TE31,8 for ITER have been carried out aiming at the achievement of the high power, the long pulse and the high efficiency operation. It was cleared that the enhancement of the gyrotron power and the extension of the pulse length were restricted by unusual oscillation due to a beam current decrease and local heating due to stray radiation loss inside the gyrotron. To solve these problems, the improvement of a radiator and an output circuit on the internal mirror were modified. Furthermore, the beam current was controlled by pre-programming of the cathode heater voltage. And, the oscillation efficiency was enhanced by improvement of the electron beam quality. As the result of these improvements, the steady state operation of 1 hour (3600 s) with the output power of 0.6 MW, which significantly exceeded the typical operation time 400 s of ITER was demonstrated. The operation of a 0.6 MW/1 hour could be obtained by the usual operation method which fixed the cavity magnetic field and the pitch factor of the electron beam. However, it was possible that the state of oscillation is controlled by changing these operation parameters during the shot in the long pulse operation. By the advanced operation mode, the gyrotron output power increased to 0.82 MW with the same beam power (the beam current and the beam voltage) of the 0.6 MW/1 hour operation. The oscillation characteristics in the long pulse operation was clarified, and the advanced operation mode of the gyrotron to the high efficiency oscillation was newly established by controlling a pitch factor of the electron beam and the cavity magnetic field in the long pulse operation. As a result, the high efficiency operation of 56 % with the output power of 0.82 MW was succeeded beyond 600 s (10 min).