On the stability of the $m=1$ rigid ballooning mode in a mirror trap with high-beta sloshing ions

Abstract

Stability of the ``rigid'' $m = 1$ ballooning mode in a mirror axisymmetric trap is studied for the case of oblique neutral beam injection (NBI), which creates an anisotropic population of fast sloshing ions. Since small-scale modes with azimuthal numbers $m>1$ in long thin (paraxial) mirror traps are easily stabilized by finite Larmor radius (FLR) effects, suppression of the rigid ballooning and flute modes would mean stabilization of all MHD modes, with the exception of mirror and fire-hose disturbances, which are intensively studied in geophysics, but have not yet been identified in mirror traps. Large-scale ballooning mode can, in principle, be suppressed either by the lateral perfectly conducting wall, or by the end MHD anchors such as cusp, or by biased limiters, or by combination of these two methods. The effect of the wall shape, vacuum gap width between the plasma column and the lateral wall, angle of oblique NBI, radial profile of the plasma pressure, and axial profile of the vacuum magnetic field are studied.