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(EX/P4-10) Ion Temperature Increase During MHD Events on the TST-2 Spherical Tokamak

A. Ejiri¹⁾, S. Shiraiwa¹⁾, Y. Takase¹⁾, H. Kasahara¹⁾, D. Iijima¹⁾, Y. Kobori¹⁾, T. Nishi¹⁾, T. Yamada²⁾, M. Ushigome²⁾, Y. Nagashima²⁾, T. Taniguchi²⁾, K. Yamagishi^2)
 
1) Graduate School of Frontier Sciences, University of Tokyo, Tokyo, Japan
²⁾ Graduate School of Science, University of Tokyo, Tokyo, Japan

Abstract.  MHD events including Internal Reconnection Events (IREs) are studied on the TST-2 spherical tokamak. Besides the previously reported IREs with positive current spikes which have drastic effects, more benign ones which have no positive current spikes or ones which have small magnetic fluctuations have been observed. Some IREs are accompanied by a rapid ion temperature increase during a current. Typical parameters of analyzed plasmas are: major radius R < 0.36 m, minor radius a < 0.23 m, aspect ratio A > 1.6, elongation k < 1.8, toroidal magnetic field B_T0 =0.15 T, plasma current I_p $\sim$70 kA, electron density $\sim$ 10¹⁹m^{- 3}, electron temperature $\sim$100 eV, ion temperature $\sim$70 eV and discharge duration $\sim$20 ms. In the case of benign MHD events, the plasma current drops without a positive spike, while bursts of magnetic fluctuations and hard X-ray emission and H_$\alpha$ were observed. In some IREs, ion temperature measured by the Doppler broadening of O^{4 +} starts to increase before the current spike, and the temperature decays to the original level after the current spike.

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