ALFVEN ION-CYCLOTRON INSTABILITY IN A MIRROR TRAP WITH HIGHLY ANISOTROPIC PLASMA

The Alfven ion cyclotron instability is studied for mirror-confined bi-Maxwellian highly anisotropic plasmas. In such plasmas the wave length of unstable modes is of the order of the plasma scale length. Another specific feature is that a typical ion can execute several bounce oscillations along the strongly non-uniform plasma during the time of the phase divergence between the wave and cyclotron rotation. Traditional approaches such as WKB method and local dispersion relation fail under these conditions. An integral equation for the modes is derived. The spatial distribution of the eigenmodes as well as the marginal stability conditions are found by numerical solution of this equation. The asymptotics of these results in the limit of infinitely large anisotropy are obtained analytically. It is found that the mirror-confined highly anisotropic plasma can be much more stable than it follows from the traditionally used scaling.