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Flux amplification of a translated field-reversed configuration plasma

Author: Tomohiko Asai
Requested Type: Consider for Invited
Submitted: 2014-05-30 02:19:06

Co-authors: J. Sekiguchi, H. Ando, M. Arai, S. Katayama, Ts. Takahashi, M. Inomoto, To. Takahashi

Contact Info:
Nihon University
1-8-14 Kanda-Surugadai
Chiyoda, Tokyo   101-830

Abstract Text:
A field-reversed configuration (FRC) is a compact toroid confined with a poloidal magnetic field[1]. Because of its extremely high-beta i.e. low magnetic field feature, an effective fusion-relevant current drive method onto an FRC is only a neutral beam injection. However, the highest quality (temperature and density) FRC formed by a field-reversal theta-pinch (FRTP) has never attained required amount of trapped poloidal flux to confine the tangentially injected fast beam ions.

Because of its simply-connected configuration, an FRC can be translated axially along a gradient of guide magnetic field, and trapped in a confinement region with quasi-static external magnetic field. The translation speed reaches a range of Alfven velocity. In this study, two methods of flux amplification during and after translation process have been evaluated on the newly built FRC machine FAT (FRC amplification via translation).

The background gas in the translation region works as a low-energy high-current axially injected NBI onto a translating FRC[2]. In the first series of FAT experiments, the FRCs translated into statically filled deuterium gas showed dramatically increased plasma volume. In the case of translation with a vacuum state, no significant increment of separatrix volume was observed. This suggests the existence of regeneration mechanism of kinetic energy of translated FRC back into internal plasma energy during the translation process.

A center solenoid (CS) has also been employed to drive toroidal plasma current. A quasi-spherical, large bore confinement region of FAT realizes application of a CS onto the geometrical axis of FRC through a topological transition of magnetic configuration from a simply-connected to a torus structure during the translation process. Initial result of the inductive current drive onto a translated FRTP-FRC will also be presented.

[1] M. Tuszewski, Nucl. Fusion 28, 2033(1988).
[2] Y. Matsuzawa, T. Asai et al., Phys. P

Characterization: 1.0,1.1

This abstract is submitted for the US-Japan Compact Torus Workshop (CT).

Workshop on Exploratory Topics in Plasma and Fusion Research (EPR) and US-Japan Compact Torus (CT) Workshop
August 5-8, 2014
Madison, Wisconsin

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