Mirror stabilization experiments in the Hanbit device

Abstract

The Hanbit magnetic mirror device has been involved in a series of experiments on stabilization of the MHD flute type mode. We undertook investigations to see whether a divertor and the kinetic stabilizer (KS) of Post et al can stabilize the MHD instability. The Hanbit divertor configuration used one of the central cell coils with reversed current as the divertor coil and two other coils with increased current to compensate the field droop. The divertor eliminated the m = −1 instability when the null point was inside the vacuum tank. The KS used microwave produced plasmas on field lines in the cusp tank region. Two coils on the cusp tank were configured to produce expanding field lines with a large positive radius of curvature. A 5 kW 2.45 GHz magnetron was used to produce an electron cyclotron resonance heated plasma pressure in this region. A reduction in instability duration was observed for high power plasmas. However, for low power plasmas that terminate violently with an m = −1 instability, the KS action made the duration of the instability longer.