Shielding of resonant magnetic perturbations in the long mean-free path regime

The effect of diamagnetic drifts and of long electron mean free path on the shielding of resonant magnetic perturbations by plasma rotation is investigated. The nature of the force exerted on a moving plasma by a resonant perturbation is qualitatively altered by both drift and long mean-free-path effects. The force is found to have three minima, each of which is a possible locus for discontinuous transitions in plasma velocity. Between these minima are two points where the force exerted by the perturbation is resonant. These points describe locked states where shielding is ineffective and a magnetic island will grow. They correspond to rotation velocities such that either the electrons or the ions are at rest in the frame of the perturbation. The ion root, however, is unstable.