Kinetics of weakly collisional plasma

Under conditions which are usually associated with collisionless plasma, and in which the mean free path of charged particles considerably exceeds the characteristic size of the spatial inhomogeneities involved, plasmas always contain slow particles whose mean free path proportional to the fourth power of their velocity is less than the inhomogeneity scale. Although relatively few in number, these subthermal particles play a dominant role in such 'weakly collisional' plasmas. In this paper, the results of the analytical kinetic theory of plasma are discussed, which highlight the determining role slow collisional particles play in such plasma phenomena as ion-acoustic wave damping and nonlinear electron-density perturbations due to the inhomogeneous intensity of the plasma-heating electromagnetic field. It is shown that by affecting these plasma properties the subthermal electrons correspondingly make an impact on parametric instabilities such as plasma radiation filamentation and stimulated Mandelstam– Brillouin scattering. Theoretical predictions are compared with numerical solutions of the Boltzmann equation. The concept of nonlocal plasma transfer processes, attracted to the interpretation of such solutions, is also discussed.