Cyclotron instability of a plasma in magnetic mirror machines

Abstract

The authors consider cyclotron instability in a homogeneous plasma with anisotropic non-monotonic ion distribution in velocity space. In the plane of the parameters and τ = ϵ⊥i/ϵ‖i (where ω0e is the plasma frequency of the electrons, ωi is the Larmor frequency of the ions, ϵ⊥i and ϵ‖i are the transverse and longitudinal energy of the ions respectively) regions are constructed by numerical methods which correspond to the unstable states of a plasma at cyclotron resonances of different orders. The authors study the dependence of these regions on electron temperature, the dimensions of the trap, and the width of the ion transverse-velocity distribution peak. The stability of a plasma in machines of the Ogra-2 type is discussed. It is shown that the results of recent experiments on the Phoenix device aimed at suppressing cyclotron instability cannot be explained by broadening of the ion distribution peak. To stabilize the oscillations in this machine it is sufficient to increase the temperature of the electrons to 30 – 50 eV, which is apparently what happens in the experiment.