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Landau Damping of Sound in a Rarefied Neutral Gas

P. Stubbe
Journal / Anthology

Phsyics of Fluids
Year: 1994
Volume: 6
Issue: 9
Page range: 3164-3174

It is shown that the damping of sound, as measured in highly rarefied neutral gases, can be quantitatively described in terms of Landau damping. The theoretical method is based on determining the unknown pressure tensor gradient in the equation of motion by using the solution of the linearized kinetic equation, treating the occurring integrals over velocity space by Landau's integration prescription. Collisions are taken into account by means of a relaxation model that meets all conservation requirements. The resulting equation of motion is formulated such that the entirety of linear kinetic effects is encapsulated in two coefficients, gamma and Gamma, which do not depend on particle charge, and are thus applicable to plasmas and neutral gases alike. The only occurrence of charges and electric fields in the equation of motion is in the form of a cold plasma force term. The coefficients gamma and Gamma are, in general, nonlocal in time and space, but become constants in certain limits. Application of the theory to neutral sound absorption leads to a good agreement with experimental data (Meyer and Sessler [Z. Phys. 149, 15 (1957)]) over the entire range of experimental parameters, from the near-collisionless to the collision-dominated limit.

*Science > Astronomy