Analysis of Acoustic Wave Phenomena in Radiation Magnetic Hydrodynamics

Abstract

The propagation of linear acoustic disturbances in an infinite, homogeneous, gray radiating plasma, initially in mechanical and radiation equilibrium, is considered. An exact governing equation for radiation acoustics in a radiating gray gas is derived, taking into account the influence of the transverse magnetic field. Radiation magnetohydrodynamics (MHD) is described by three hydrodynamic equations and two radiative momentum equations, making extensive use of the formalism of radiation thermodynamics. With the aim of more reliably describing the evolution of radiation magnetic–acoustic disturbance waves with scattering and attenuation, the conditions of radiation-thermal dissipation, the force of radiation resistance, as well as magnetic force and Joule heat are introduced into these equations. In this case, the Eddington approximation is used, which allows one to study the modes of radiation magnetohydrodynamic waves in two asymptotic cases—optically thin and thick gas. The exact control equation derived in the work made it possible, using the heuristic Whitham method, to obtain a set of approximate control equations of the lowest order, each of which is part of a reliable approximation to the exact equation in a certain region of the independent time variable. The relatively simple form of such equations made it possible to study the physical processes occurring in each radiation magnetic–acoustic wave without a formal solution to the full problem.