Generalized energy principle for flute perturbations in axisymmetric mirror machines.

摘要

Axial symmetry is a very desirable property of the mirror devices both for fusion and neutron source applications. The main obstacle to be circumvented in the development of such systems, is the flute instability of axisymmetric mirrors. In recent years there appeared a number of proposals, devoted to the stabilization of the flute perturbations in the framework of axisymmetric magnetic configurations, which are based on the combining of the MHD unstable central cell with various types of end-cell stabilizers. In the present paper we concentrate ourselves just on this scheme, including long solenoid with a uniform field, conjugated with the end stabilizing anchor, intended to provide MHD stability of the system as a whole. The attractive feature of such a configuration is that it allows to exploit finite larmor radius (FLR) effects for the stabilization of the flute perturbations. As is well known, FLR effects, being strong, stabilize all flute modes, except the one with azimuthal number m = 1, corresponding to the ''rigid'' displacement of the plasma column (the ''global'' mode). Consequently, in the conditions when FLR effects dominate, the anchor has to stabilize the ''global' mode only. Bearing in mind a favorable influence of FLR effects we, however, don't restrict our paper by discussion of only ''global'' mode stability and consider a general case of an arbitrary azimuthal mode.