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(EX/P3-15) High-Beta Characteristics of First and Second-Stable Spherical Tokamaks in Reconnection Heating Experiments of TS-3

Y. Ono¹⁾, T. Kimura¹⁾, Y. Murata¹⁾, S. Miyazaki¹⁾, Y. Ueda¹⁾, M. Inomoto¹⁾, A.L. Balandin¹⁾, M. Katsurai^1)
 
1) High Temperature Plasma Center, University of Tokyo, Tokyo, Japan

Abstract.  Novel formations of ultra-high-beta Spherical Tokamak (ST) have been developed in the TS-3 device using high power heating of merging/ reconnection. In Type-A merging, two STs were merged together to build up the plasma beta. In Type-B merging, an oblate FRC was initially formed by merging of two spheromaks with opposing toroidal field B_t. and was transformed into an ultra-high-beta ST by applying external B_t. Ballooning stability analyses confirmed formations of the first-stable STs by Type-A merging and the second-stable STs by Type-B merging and also the unstable STs by both mergings, revealing the ballooning stability window consistent with measured high-n instabilities. We made (1) those model analyses of the produced STs for the first time using the BALLOO stability code, revealing that hollowness/ broadness of current/ pressure profiles widen significantly the window to the second-stable regime. This paper also addresses (2) normalized betas of the second-stable STs as large as 6-17 for comparison with the Troyon scaling and (3) a promising scaling of the reconnection heating energy.

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