Dynamic process during axial magnetic compression of field-reversed configuration for equilibrium shape control

Adiabatic magnetic compression experiments on a field-reversed configuration (FRC) plasma are reported. The compression is performed on a long FRC held in a straight mirror field. The separatrix length of the FRC is limited by the distance between the magnetic mirrors. The mirror distance is compressed in time to 35% of the original one by the compression coil installed inside the chamber, and the separatrix length is shortened to 38%. The separatrix radius of the compressed FRC increases by 56% and the aspect ratio (separatrix length/separatrix diameter) changes from 12.6 to 4.1. Magnetic probes with the compensation circuit are utilized to investigate the dynamic transition phase during the compression. The transition process is found from these measurements to be divided into three stages, where a new equilibrium state is achieved in the final stage.