Magnetoacoustic nonlinear waves in a heat-releasing plasma

The evolution of weak magnetoacoustic waves in a heat-releasing completely ionized plasma medium with a thermal instability is investigated. The nonlinear magnetoacoustic equations describing the evolution of fast and slow magnetoacoustic waves are obtained. The correlation between the obtained nonlinear magnetoacoustic equations and the nonlinear acoustical equation of nonequilibrium medium with exponential relaxation law is shown. The dispersion properties of the wave modes existing in the plasma medium are discussed. The acoustic amplification and damping conditions are defined by solving the dispersion relation. The influence of the thermal conduction and finite electrical conductivity on the process of nonlinear acoustical structure formation is discussed. The shape and parameters of the magnetoacoustic pulse that is an automodel solution of this equation under conditions of magnetoacoustic thermal instability have been determined analytically. Results of the numerical simulation of the full one-dimensional system of magneto-hydrodynamics equations are compared with the solutions of the nonlinear magnetoacoustic equation obtained for these unstable regions. The disintegration of any initial weak perturbation of compression into sequence of self-sustained magnetoacoustic pulses is shown numerically.