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(EX7/5) Ultra-High-Beta Spherical Tokamak with Absolute Minimum-B in TS-3 Spherical Torus Experiments

Y. Ono¹⁾, M. Inomoto¹⁾, Y. Ueda¹⁾, M. Katsurai¹⁾, T. Matsuyama¹⁾, Y. Murata¹⁾, T. Tawara^1)
 
1) High Temperature Plasma Center, University of Tokyo

Abstract.  An absolute minimum-B configuration was obtained when applied external toroidal magnetic field transformed a field-reversed configuration (FRC) into an ultra-high-beta (> 50%) spherical tokamak (ST). High-power heating ($\approx$ 5-30MW) of magnetic reconnection was used to form the oblate FRC and to increase thermal pressure (beta) of STs. High-beta STs with a variety of pressure and q profiles revealed their stability boundaries and possible ballooning collapses. The high-beta ST with maximum pressure gradient p_$\Psi$ in the periphery was maintained stably, while another high-beta ST with maximum p_$\Psi$ in the core collapsed due to high-n ( n > 8) localized modes.

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