Plasma and Fusion Research

Volume 13, 3402114 (2018)

Regular Articles

Current Drive Experiment Using Top/Outboard Side Lower Hybrid Wave Injection on TST-2 Spherical Tokamak
Satoru YAJIMA, Yuichi TAKASE, Akira EJIRI, Naoto TSUJII, Hibiki YAMAZAKI, Charles P. MOELLER1), Takahiro SHINYA2), Yuki TAKEI, Yoshiyuki TAJIRI, Yusuke YOSHIDA, Akito SATO, Akichika KITAYAMA and Naoki MATSUMOTO
The University of Tokyo, Kashiwa 277-8561, Japan
1)
General Atomics, San Diego, CA 92186, USA
2)
National Institute for Quantum and Radiological Science and Technology, Rokkasho 039-3212, Japan
(Received 27 December 2017 / Accepted 3 August 2018 / Published 25 September 2018)

Abstract

In the TST-2 spherical tokamak device, we carried out a fully non-inductive current startup experiment by Landau damping of the Lower Hybrid Wave (LHW). Capacitively Coupled Combline Antennas (CCCAs) were used for wave injection. The antennas are located on the outboard side and the top side of the vacuum vessel, and by reversing the toroidal magnetic field, it is possible to simulate the case of wave injection from the bottom side. The highest plasma current of 26.7 kA was achieved by top injection with the reversed toroidal magnetic field. According to numerical calculation using ray tracing and Fokker-Planck codes (GENRAY/CQL3D), the downshift of the parallel wavenumber helped the tail of the electron velocity distribution extend to higher energy than the other cases. Additionally, in order to evaluate the directionality of the wavenumber spectrum which is also important for efficient current drive, a finite element solver (COMSOL) was used. In order to avoid deterioration of the wavenumber spectrum, one limiter of the outboard antenna should be moved away toroidally by 70 mm from the current position, and the preferred distance between the antenna and the cutoff density layer is about 2 cm.

Keywords

spherical tokamak, lower hybrid wave, non-inductive plasma start-up

DOI: 10.1585/pfr.13.3402114

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