@article{oai:repo.qst.go.jp:00048868,
 author = {假家, 強 and 今井, 剛 and 南, 龍太郎 and 坂本, 慶司 and 小田, 靖久 and 池田, 亮介 and 下妻, 隆 and 久保, 伸 and 出射, 浩 and 沼倉, 友晴 and 津村, 康平 and 江橋, 優斗 and 岡田, 宏太 and 中嶋, 洋輔 and 吉村, 泰夫 and 高橋, 裕己 and 伊藤, 哲 and 花田, 和明 and 長崎, 百伸 and 小野, 雅之 and 江口, 濯 and 満仲, 義加 and 坂本 慶司 and 小田 靖久 and 池田 亮介},
 issue = {6},
 journal = {Nuclear Fusion},
 month = {Apr},
 note = {Megawatt power gyrotrons are being developed for collaborative electron cyclotron heating (ECH) studies of advanced fusion devices and demonstration power plant (DEMO). (1) In the first experiment of a 300 GHz gyrotron, an output power above 0.5 MW in the TE32,18 single mode was achieved with a pulse width of 2 ms. This was the first observation of MW-scale oscillations in a DEMO-relevant gyrotron mode. It was also found that the reflection at the output window affected the determination of the oscillation mode. Furthermore, several single mode oscillations in the 226–254 GHz range were confirmed, which is important for the step-frequency tunable gyrotron in the sub-THz frequency range. (2) Based on the successful results of the 77 and 154 GHz large helical device (LHD) tubes, a new 154/116 GHz dual-frequency gyrotron with an output of over 1.5 MW is being designed. (3) A new record output of 1.38 MW was obtained using an existing 28 GHz gyrotron. A newly designed tube aimed at achieving a dual-frequency output power of 2 MW at 28 GHz (0.4 MW continuous wave) and 1 MW at 35 GHz was built. In the first experimental test, main mode oscillations were observed at the frequencies of 28.036 and 34.831 GHz with Gaussian-like output beams and output power of 1.27 and 0.48 MW, respectively. A total efficiency of 50% was achieved at 28 GHz operation.},
 pages = {066001 -1--066001 -9},
 title = {Development of over-MW gyrotrons for fusion at 14 GHz to sub-THz frequencies},
 volume = {57},
 year = {2017}
}