MERGING FORMATION OF FRC AND ITS APPLICATION TO HIGH-BETA ST FORMATION

MERGING FORMATION OF FRC AND ITS APPLICATION TO HIGH-BETA ST FORMATION ONO Y., INOMOTO M., UEDA Y., MATSUYAMA T., OHSHIMA Y., KATSURAI M. 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-ß ST by applying external toroidal field Bt,ext. The toroidal field was observed to vanish around magnetic axis after the Bt,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-ß 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 Bt,ext did the FRC into the ultra-high-ß (>60%)/diamagnetic ST, indicating the close relationship between FRC and ST in second stability.