Transmission of acoustic wave energy across a magnetic flux sheath

Abstract

The transmission of the energy of an acoustic wave incident on a magnetic flux sheath embedded in a homogeneous nonmagnetic plasma is analyzed for the case where finite current sheets are situated between the flux sheath and the nonmagnetic region outside. It is assumed that the magnetic field in the current sheets has a constant spatial gradient along the x-direction, levels off at a constant value in the flux sheath, continues through the flux-sheath thickness, and then reduces symmetrically to zero at the edge of the field-free plasma. The transverse transmission efficiency of an acoustic wave whose wavelength is implied to be equal to the thickness of the flux sheath is computed for specific values of the relevant parameters; the calculation is also performed for an acoustic wave of the same wavelength propagating across a flux sheath bounded by infinitesimally thin current sheets. It is found that the structure with finite current sheets allows less transmission of acoustic waves for identical values of the relevant parameters, but the transmission efficiency is of the same order of magnitude for both kinds of magnetic structure.