Generation of acoustic waves by alfven waves at a diffusive boundary with an un-ionized medium

Yu. N. Savchenko - L. P. Gorbachev

Abstract
Two media are considered, one un-ionized and the other a partially ionized cold plasma, which are separated by a layer formed by diffusion of charged particles into the un-ionized region. The properties of the medium are assumed to be uniform in the horizontal directions and non- uniform along the directionoffree-fallacceleration. The excitation of acoustic waves by Alfven waves is studied for small angles of inclination of the external magnetic field to the vertical. The medium is treated as a three-component gas consisting of ions, electrons, and neutral particles. The frequencies studied are much larger than the collision frequencies between neutral and charged particles, and much less than the ion-cyclotron frequencies. The pressure in an acoustic wave generated by an Alfven wave in a diffusive layer with a gyrotropic conductivity is determined. A generation coefficient is introduced for the acoustic waves and its behavior as a function of the wave frequency and medium parameters is examined. It is shown that the most intense wave coupling occurs at low frequencies. The existence is noted of local extrema in the behavior of the generation coefficient which are explained by the appearance of resonance properties in the region of most intense generation of acoustic waves.