[Table of Contents]

Plasma and Fusion Research

Volume 8, 1402023 (2013)

Regular Articles

Merging Experimental Study of High-Beta ST Formation for Non-Inductive Plasma Start-Up Assisted by NBI in TS-4
Keii GI, Toru II1), Toshiyuki UMEZAWA, Michiaki INOMOTO and Yasushi ONO
Graduate School of Frontier Sciences, The University of Tokyo, Chiba 277-8561, Japan
1)
Graduate School of Engineering, The University of Tokyo, Tokyo 113-8656, Japan
(Received 14 November 2012 / Accepted 18 February 2013 / Published 27 March 2013)

Abstract

Spherical tokamak (ST) merging start-up for high-beta ST formation was developed in the TS-4 merging/reconnection experiment under a high external toroidal magnetic field. We optimized the formation of a stable high-beta ST (βt > 30%) by adjusting the initial parameters of two low-beta STs. We precisely analyzed the produced high-beta STs by MEUDAS using the measured and fitted profiles, and found that they exhibited low-plasma internal inductance because of a hollow current profile, a paramagnetic toroidal field, and weakly reversed shear. A pressure-driven instability analysis indicates that the merging STs become unstable when their q-values are less than 1. In the first high-power neutral beam injection experiment (#1 and #2, PNBI ∼ 0.4 MW) in TS-4, the decay time and magnetic flux of the produced STs were improved, mainly because of pre-ionization and merging/reconnection effects.

Keywords

ST, non-inductive start-up, plasma merging, magnetic reconnection, high-beta, NBI, MHD equilibrium reconstruction, pressure-driven instability

DOI: 10.1585/pfr.8.1402023

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References

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This paper may be cited as follows:

Keii GI, Toru II, Toshiyuki UMEZAWA, Michiaki INOMOTO and Yasushi ONO, Plasma Fusion Res. 8, 1402023 (2013).