X-ray Measurements during Plasma Current Start-up Experiments using the lower hybrid wave on the TST-2 spherical tokamak

Takuma Wakatsuki, Akira Ejiri, Hidetoshi Kakuda, Yuichi Takase, Takanori Ambo, Hirokazu Furui, Takahiro Hashimoto, Junichi Hiratsuka, Hiroshi Kasahara, Kunihiko Kato, Ryuhei Kumazawa, Yoshihiko Nagashima, Kenji Saito, Takuya Sakamoto, Tetsuo Seki, Fujio Shimpo, Ryota Shino, Takahiro Shinya, Masateru Sonehara, Osamu WatanabeTakashi Yamaguchi, Charles P. Moeller

    Research output: Contribution to journalArticlepeer-review

    4 Citations (Scopus)


    Non-inductive plasma current start-up experiments using RF power in the lower hybrid frequency range is being conducted on the TST-2 spherical tokamak. Plasma currents of up to 15 kA have been achieved. The effect of direct current drive can be seen by comparing the cases with co-drive and counter-drive. X-rays in various energy ranges were measured to investigate the interaction between the wave and the electrons. Soft X-ray (SX) measurements revealed that the perpendicular SX emission increased significantly as the plasma current increased, and that the tangential SX emission in the direction of RF drive was enhanced more strongly in the co-drive case compared to the counter-drive case. These observations imply that the fast electrons accelerated by the lower hybrid wave contribute to the plasma current. However, RF amplitude modulation experiments showed that the confinement time of these fast electrons are very short (less than 0.05 ms), much shorter than the collisional slowing down time. Hard X-ray spectral measurements showed that the radiation temperature of fast electrons in the co-direction for current drive was higher than that in the counter-direction. These observations are consistent with the existence of RF-driven fast electrons.

    Original languageEnglish
    Pages (from-to)485-489+5
    JournalIEEJ Transactions on Fundamentals and Materials
    Issue number7
    Publication statusPublished - 2012

    All Science Journal Classification (ASJC) codes

    • Electrical and Electronic Engineering


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