Plasma and Fusion Research

Volume 17, 2405090 (2022)

Regular Articles

Absorption Analysis of Electron Cyclotron Waves in the Magnetospheric Plasma Device RT-1
Takahiro MORI1), Masaki NISHIURA1,2), Naoki KENMOCHI2), Kenji Ueda1), Takuya Nakazawa1) and Zensho Yoshida2)
1)
Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Chiba 277-8561, Japan
2)
National Institute for Fusion Science, Toki 509-5292, Japan
(Received 10 January 2022 / Accepted 1 June 2022 / Published 24 August 2022)

Abstract

The absorption efficiency of electron cyclotron heating is investigated theoretically and experimentally to understand the wave heating mechanisms under the overdense state and the density limit. The features of self-organizing mechanisms have been observed in the dipole confinement system [M. Nishiura et al., Nucl. Fusion 55, 053019 (2015)]. The modulated 2.45 GHz electromagnetic (EM) wave is applied to the RT-1 plasmas to evaluate the EM wave's absorption efficiency from the diamagnetic signals' response. The absorption efficiency maintains a constant 100% beyond the O-mode's cutoff density. However, it decreases rapidly near the 1.6 × 1017 m−3 line-averaged density, which is twice higher than the 2.45 GHz O-mode cutoff. At less than 0.6 × 1017 m−3, the absorption efficiency simulated by a ray-tracing code in a two-dimensional model explains the experimental absorption efficiency. However, it deviates from the experimental value near the cutoff density and is more significant at the density limit. We discuss the difference between the experimental and numerical results.

Keywords

magnetospheric plasma, electron cyclotron heating, electron cyclotron wave, overdense plasma, electromagnetic wave propagation

DOI: 10.1585/pfr.17.2405090

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