Second harmonic EC plasma ramp-up through production of energetic electrons on the QUEST spherical tokamak

POSTER

Abstract

Plasma current is started up solely by electron cyclotron wave (ECW) in QUEST spherical tokamak. The beam of 28 GHz second harmonic ECW is injected obliquely from low field side, and hence parallel refractive index at the resonant layer is N|| = 0.78. A steering antenna, consisting of two quasi-optical mirrors, can turn direction of the focused Gaussian beam. Polarization of the ECW is controlled as X-mode is superior to O-mode. In the experiment, achieved peak plasma current has been high record, as non-inductive RF start-up, reaching Ip > 75 kA. The count number and the averaged energy of Hard X-ray attributed to energetic electrons increase with Ip ramp-up. Analysis through TASK-WR simulation demonstrates that power of 28 GHz ECW is absorbed dominantly to energetic electrons via single-pass cyclotron damping, and that X-mode absorption into particle is adequately higher than that of O-mode.

*This work is supported by MEXT funding for young scientists associated with active promotion of national university reforms, and NIFS Collaboration Research program (NIFS13KUTR085, NIFS17KUTR128)

Presenters

  • Takumi Onchi

    • Kyushu Univ

Authors

  • Takumi Onchi

    • Kyushu Univ

  • Hiroshi Idei

    • Kyushu University
    • Kyushu Univ

  • Makoto Hasegawa

    • Kyushu Univ

  • Kengoh Kuroda

    • Kyushu Univ

  • Ryuya Ikezoe

    • Kyushu Univ

  • Kazuaki Hanada

    • Kyushu University
    • Research Institute for Applied Mechanics, Kyushu University, 816-8580, Fukuoka, Japan
    • Kyushu Univ

  • Akira Ejiri

    • Univ of Tokyo

  • Tsuyoshi Kariya

    • Univ of Tsukuba

  • Shin Kubo

    • National Institute for Fusion Science, Nagoya Univ.
    • NIFS, Japan
    • NIFS

  • Toru Tsujimura

    • National Institute for Fusion Science
    • NIFS

  • Atsushi Fukuyama

    • Kyoto Univ