Screw and flute instabilities in a low-pressure plasma

Abstract

A plasma can escape across a magnetic field as a result of instabilities which produce an electric field and an associated transverse drift motion. The electric field is due to a charge separation which arises from a differential motion between ions and electrons. Such a motion can take place both in the longitudinal and the transverse directions of the magnetic field. For the former a helical perturbation of the density distribution may become the source of a screw-type instability. For the latter a transverse perturbation of the same distribution may lead to a flute-type instability. The present paper gives a survey of different effects which produce screw and flute instabilities in a fully ionized plasma. It also demonstrates the close connexion between their driving mechanisms. A number of special solutions are studied in detail. They apply to the conditions of a rotating plasma, to magnetic compression effects, finite Larmor radius effects, and to viscous effects produced by ion-ion collisions.