Axial feedback stabilization of flute modes for mirror machines

A novel scheme of feedback stabilization of the m=1 flute mode for axisymmetric mirror machines is proposed that has potential for reactor extrapolation. A three-region plasma model is analyzed, consisting of a hot core surrounded by a warm transition annulus, which in turn is surrounded by a warm halo annulus that is in contact with segmented annular feedback plates at the two end walls. For plasma parameters characteristic of the TMX-U and MFTF-B devices at the Lawrence Livermore National Laboratory and the MMX device at the University of California, Berkeley, the required feedback power is calculated. The results show that stability can be achieved in the MMX and TMX-U devices with a modest feedback gain and power. The power requirement for the near-reactor conditions of MFTF-B is more severe, but can be reduced by a modified choice of plasma parameters