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(EXP4/12) Merging Formation of FRC and its Application to High-Beta ST Formation

Y. Ono, M. Inomoto, Y. Ueda, T. Matsuyama, Y. Ohshima, M. Katsurai

Department of Electrical Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113, Japan

Abstract.  Merging formation of field-reversed configuration (FRC) explored not only a new scenario of highly-efficient FRC formation/amplification experiment but also a new boundary research between FRC, spheromak and spherical tokamak (ST). A new finding is that the produced FRC is transformed stably into an ultra-high-$\beta$ ST by applying external toroidal field B_{t, ext}. The toroidal field was observed to vanish around magnetic axis after the B_{t, ext} application to the FRC, indicating formation of diamagnetic ST. The hollow current profile of FRC was maintained during the equilibrium transition, eliminating a need for the difficult hollow-current-formation process of start-up discharge of high-$\beta$ ST. The energy-conversion effect of merging transformed the force-free merging spheromaks with paramagnetic current into the FRC with diamagnetic current and the further application of B_{t, ext} did the FRC into the ultra-high-$\beta$ (> 60%)/diamagnetic ST, indicating the close relationship between FRC and ST in second stability.

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