Plasma and Fusion Research

Volume 16, 2402024 (2021)

Regular Articles

Effects of Toroidally Distributed Divertor Biasing on Scrape-Off-Layer Plasma in the QUEST Spherical Tokamak
Kazuo TOI, Takumi ONCHI1), Kengo KURODA1), Shinichiro KOJIMA1), Hideki ZUSHI1), Makoto HASEGAWA1), Masaharu FUKUYAMA1), Shoji KAWASAKI1), Aki HIGASHIJIMA1), Tatsuya IKEZOE1), Hiroshi IDEI1), Takeshi IDO1), Kazuaki HANADA1) and QUEST Experiment Group1)
National Institute for Fusion Science, Toki 509-5292, Japan
Research Institute for Applied Mechanics, Kyusyu University, Kasuga 816-8580, Japan
(Received 18 November 2020 / Accepted 7 January 2021 / Published 5 March 2021)


A novel divertor biasing using four biasing plates that are arranged toroidally every 90° on the upper divertor plate is applied to low-density plasmas of the QUEST spherical tokamak. When some of these plates are biased in-phase by applying a sawtooth waveform voltage of 85-V amplitude and 50-Hz repetition, up to approximately 35% reduction of the particle flux to the divertor is observed during positive biasing. The input power for the flux reduction is approximately 0.2 kW for low-density tokamak plasmas produced by ∼130-kW electron cyclotron wave injection. Additionally, the signal of a plate probe placed in the low-field side of the mid-plane of the vacuum vessel indicates enhanced losses of fast electrons during positive biasing. The enhanced loss is attributed to small resonant magnetic perturbations produced by the bias-driven currents in the scrape-off layer. This novel divertor biasing is expected to provide a new experimental tool for studying divertor heat load control and fast electron confinement in a tokamak device.


scrape-off layer (SOL), divertor heat load, divertor biasing, radial transport in SOL, SOL current, resonant magnetic perturbation

DOI: 10.1585/pfr.16.2402024


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