Merging formation and current amplification of field-reversed configuration

The merging formation of the field-reversed configuration (FRC) has been developed in the TS-3 merging experiment, leading us to a new scenario of FRC slow formation, heating and current amplification. Two force-free spheromaks with opposing toroidal fields were merged together in the axial direction to form a high-beta FRC with higher efficiency than the conventional field-reversed theta-pinch method. This unique relaxation from the force-free (beta similar to 0.05 - 0.1) spheromaks to the high-beta (beta similar to 0.7 - 1) FRC is attributed to the conversion of toroidal magnetic energy into ion thermal energy through the reconnection outflow. A central ohmic heating (OH) coil worked successfully to amplify the FRC plasma current by a factor of 2. Toroidal mode analysis of magnetic structure indicated that the tilting stability of the oblate FRC was provided by an ion kinetic effect. This oblate FRC is also useful as an initial equilibrium to produce a high-beta(p) spherical tokamak (ST) with diamagnetic toroidal magnetic field, suggesting the close relationship between FRCS and high-beta(p) STs in the second stable region of the ballooning mode. (c) 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.