Plasma and Fusion Research

Volume 17, 2402039 (2022)

Regular Articles

Investigation of Capability of Current Control by Electron Cyclotron Waves in the Quasiaxisymmetric Stellarator CFQS
Yasuo YOSHIMURA1), Motonari KANDA1), Ryoma YANAI1), Akihiro SHIMIZU1,2), Shigeyoshi KINOSHITA1), Mitsutaka ISOBE1,2), Shoichi OKAMURA1), Kunihiro OGAWA1,2), Hiromi TAKAHASHI1,2), Takanori MURASE1), Sho NAKAGAWA1), Hiroyuki TANOUE1), Haifeng LIU3) and Yuhong XU3)
1)
National Institute for Fusion Science, National Institutes of Natural Sciences, Toki, Gifu 509-5292, Japan
2)
The Graduate University for Advanced Studies, SOKENDAI, Toki, Gifu 509-5929, Japan
3)
Institute of Fusion Science, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu, China
(Received 9 January 2022 / Accepted 3 March 2022 / Published 13 May 2022)

Abstract

The capability of plasma current control by the second harmonic electron cyclotron current drive in the quasiaxisymmetric stellarator CFQS is investigated. We used the ray-tracing code TRAVIS to evaluate the electron cyclotron (EC) wave power deposition and driven current. In the standard magnetic field configuration of CFQS, the poloidal distribution of the magnetic field is nearly axisymmetric, i.e., equivalent at all toroidal positions as tokamaks. In the calculation, a flat electron density profile at the core region with ne0 = 1 × 1019 m−3 and a center-peaked electron temperature profile with Te0 = 3.5 keV are assumed. The EC wave beam direction is scanned mainly in the toroidal direction, aiming at the plasma axis. The vertical injection angle of the beam and magnetic field strength are varied and optimized to keep on-axis power deposition to maximize driven current at each toroidal direction of the EC wave beam. According to the calculation, the maximum driven current at optimum beam direction, with an expected maximum EC wave power of 400 kW, is approximately 80 kA. Meanwhile, approximately 26 kA of bootstrap current in CFQS with the volume-averaged β value of 1.2% is estimated using the BOOTSJ code. Hence, sufficient on-axis EC-driven current can be expected for compensation of the possible bootstrap current, although the current profiles are different. Moreover, a driven current of over 30 kA can be expected even in extreme cases where the magnetic field on-axis has ripples by modified modular coil currents by 20%. The possibility of compensation of bootstrap current in total amount and current profile is also discussed.

Keywords

electron cyclotron current drive, ECCD, quasiaxisymmetric stellarator, CFQS

DOI: 10.1585/pfr.17.2402039

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