Magnetic field structure evolution in rotating magnetic field plasmas

Abstract

A study of magnetic field structure evolution during 40-ms plasma discharge has been performed in a new device with 80cmlong/40cm diameter cylindrical chamber, in which a plasma current Ip≈2kA was driven and sustained by a rotating magnetic field. The main focus of the experiments is on how the changes in externally applied magnetic field affect the current profile and magnetic field in plasma. During plasma discharge, a pulse current was briefly fed to a magnetic coil located at the midplane (middle coil). The magnetic field in cross section of plasma was scanned with pickup probes. Two regimes were studied: without and with an external toroidal field (TF) produced by axial Iz current. With a relatively small current (Im⩽600A) in the middle coil, the plasma current is boosted up to 5kA. The magnetic flux surfaces become extended along the axial Z direction, sometimes with the formation of doublet shape plasma. The regime without TF appears to be less stable, presumably due to the reversal of plasma current in central area of plasma column.