Quasi-linear plasma theory (theory of a weakly turbulent plasma)

The basic principles of the quasi-linear theory of a weakly turbulent plasma are presented. Several processes occurring in a plasma in which collective degrees of freedom are excited are considered: the dynamics of noise build-up in an unstable plasma, the interaction of a beam of charged particles with the plasma, the damping of the plasma waves. The properties of the stationary weakly turbulent state arising in a plasma when a current passes through it are discussed, and so also is the problem of the anomalous diffusion of the plasma across a magnetic field. The phenomenon of `threshold absorption' of large amplitude waves in a plasma, leading to the collisionless heating of the particles, is also examined.