A formalism is presented which is suitable for the analysis of a collisionless plasma sheet confined by a static magnetic field in the presence of a small-amplitude alternating electromagnetic field. Each particle is described by angular and action variables which allow the calculation of the stationary state of the plasma in the presence of the alternating field by a variational method. A dispersion relation for the actual eigenmodes of the plasma is also derived.This formalism is used to study a stabilizing effect of the alternating field which takes place when the field has a standing-wave structure along the direction of the confinement. This effect is connected with the mean particl e velocities which are induced along the direction of the diamagnetic current. It is shown that th e drift modes and the interchange modes in the plasma may be stabilized, when discarding the parametric amplification effects and the non-linear Landau effects, if the values assumed by these mean velocities are spread over an interval of the order of the diamagnetic velocity.
Intrinsic suppression of turbulence in linear plasma devices