Non-Markovian scattering and the condition of applicability for the quasiclassical description of collisions in plasma

Abstract

It is shown that because of the non-Markovian character of momentum transfer the scattering of a test particle in plasma cannot always be described by a diffusion process. The braking of a particle by plasma occurs in three different stages: short and long times, when scattering is nondiffusive, and intermediate times, when scattering can be described by a diffusion process. The mechanism responsible for nondiffusive scattering at long times results in a new condition of applicability of classical mechanics for describing collisions in plasma v _T >ℏω_pe/m _e e ² L, where L is the Coulomb logarithm and e, m _e , and ω_pe are, respectively, the electron charge and mass and the plasma frequency. A high-temperature, almost ideal, plasma is an example of a medium where the instantaneous character of collisions makes the classical description applicable even when binary collisions should be described by quantum mechanics (the Born approximation), i.e., the plasma demonstrates the possibility of suppression of quantum effects by collective interaction.