A new collisional relaxation model for small deviations from equilibrium

Abstract

A new collisional relaxation model, applicable to small deviations from equilibrium, is established. In distinction from previous models, the new model involves three different collision frequencies for momentum transfer, energy transfer and randomization, extends the relaxation function to include the full pressure tensor rather than only its trace, and describes relaxation to individual rather than composite Maxwellian distributions. The new model is deduced in §2, and the final result is represented by equations (28) to (31). Simplified versions of the model are given in §3, and all relevant collision frequencies are quantitatively specified there. In §4, the model is applied to the kinetic theory of waves in a magnetized two-component plasma. As a particular example, magnetosonic waves are discussed for the sake of demonstrating a wave damping mechanism due to incomplete collisional activation of translatorial degrees of freedom.