Plasma and Fusion Research
Online ISSN : 1880-6821
ISSN-L : 1880-6821
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Merging Experimental Study of High-Beta ST Formation for Non-Inductive Plasma Start-Up Assisted by NBI in TS-4
Keii GIToru IIToshiyuki UMEZAWAMichiaki INOMOTOYasushi ONO
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2013 Volume 8 Pages 1402023

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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.

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© 2013 by The Japan Society of Plasma Science and Nuclear Fusion Research
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