Evolution modeling of fast and slow magnetoacoustic waves in thermally unstable plasma

Abstract

The nonlinear evolution of fast and slow magnetoacoustic waves in the plasma medium with non-adiabatic heating/cooling processes is under consideration. The magnetic field is assumed to be inclined at an arbitrary angle to the direction of wave propagation. The non-adiabatic processes depend on temperature and density and result in the steady non-equilibrium state of the medium. The steady state caused by the balance between heating and cooling rates makes it possible for thermal instabilities to appear. This research is focused on the wave mode of thermal instability (isentropic instability). The presence of other modes of the thermal instability is neglected. The isentropic instability influences on acoustic and magnetoacoustic waves and causes wave amplification. Linear analysis predicts simultaneous amplification of fast and slow magnetoacoustic waves with different increments. Furthermore, analysis predicts simultaneous disintegration of fast and slow waves on the sequences of autowave (self-sustaining) shock pulses. Numerical simulation of full system of one-dimensional magneto-hydrodynamic equations supports these results. The parameters of described autowave pulses are in good agreement with values predicted by our analytical model.