Magnetoacoustic heating in a quasi-isentropic magnetic gas
The nonlinear heating of a plasma which associates with the transfer of energy of magnetoacoustic waves into that of the entropy mode, is analytically studied. A plasma is uniform and motionless at equilibrium. Perturbations in a plasma are described by a system of ideal magnetohydrodynamic equations. The equilibrium straight magnetic strength and the wave vector form a constant angle which varies from 0 to π/2. There exist four magnetosound branches (two slow and two fast) which differ by the speed and direction of propagation in this geometry. Various cases of a nonlinear flow take place due to the kind of external source of energy. This may make plasma isentropically or/and thermally unstable. We consider magnetoacoustic heating which is excited by any one of the magnetosound perturbations in the different cases of a flow. The nonlinear instantaneous equations, which describe the dynamics of the entropy mode in the field of intense magnetoacoustic perturbations, are analytically derived and discussed in regard to some physically meaningful cases. We use special projecting in order to derive weakly nonlinear evolutionary equations.
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