Nonlinear Mirror Modes in a Plasma with Nonzero Electron Temperature

Abstract

The nonlinear theory of magnetic mirror instability (MI) accounting for the nonzero electron temperature effect is developed. Using our previous low‐frequency approach to the analysis of this instability but including nonzero electron temperature effect a set of equations describing nonlinear dynamics of mirror modes was derived. In the linear limit a Fourier transform of these equations recovers the linear MI growth rate in which the finite ion Larmor radius and nonzero electron temperature effects are taken into account. When the electron temperature Te becomes of the same order as the parallel ion temperature T‖ the growth rate of the mirror instability is reduced by the presence of the parallel electric field. The latter arises because the electrons are dragged by nonresonant ions which are mirror accelerated from regions of high into regions of low parallel magnetic flux. The nonzero electron temperature effect also substantially modifies the mirror mode nonlinear dynamics. It is found that when Te≃T‖ the transition from the linear to nonlinear regime occurs already for the wave amplitude twice smaller than that inherent to the cold electron temperature limit. The further nonlinear dynamics develops with the explosive formation of the magnetic holes and then ends with the saturated state in the form of solitary structures or cnoidal waves. It is shown that incorporation of nonzero temperature results in a weak decreases of the spatial dimensions of the holes and increase of their depth.