RF stabilization of high-density plasma in an axisymmetric mirror I: Identification and stabilization of flute mode

Abstract

The low-frequency instability observed in an axisymmetric mirror is identified as a curvature-driven flute instability for a wide range of densities up to 1014cm−3. It is demonstrated that this flute instability is stabilized by the RF field which is coupled electromagnetically and applied only in the bad-curvature region. Radial plasma loss is significantly reduced by the stabilization. This method of stabilization is revealed to be effective for densities from 1010 to 1014cm−3, indicating the possibility of a purely axisymmetric tandem mirror.