MEASUREMENTS OF ION ANGULAR VELOCITY OF FIELD REVERSED CONFIGURATION WITH SUPPRESSED ROTATIONAL INSTABILITY

The angular velocity OMEGA-c of the impurity ions (CV) is measured spectroscopically for the FRC (Field-Reversed-Configuration) plasmas confined in the theta-pinch region and translated into the confinement region with magnetic mirror field. The FRC plasma confined in the theta-pinch region becomes unstable due to the n = 2 rotational instability which can be suppressed by the multipole magnetic field. The ion rotation in the stabilized plasma is almost equal to the velocity in the unstabilized case, suggesting that the multipole field acts on the plasma surface due to the skin effect and suppresses the instability without changing the field configuration within the separatrix radius. The FRC plasma translated in the confinement region is stable without destructive instability. The ion rotation in such a plasma indicates that a suppression mechanism of the n = 2 instability exists, which is excited by the rotation in the confinement region.