Dynamic Stabilization of a Plasma Column

A cylindrical plasma column is confined by a magnetic field whose z component is constant while the φ component oscillates sinusoidally. The skin depth is assumed to be negligible so that the boundary can be considered as sharp and the interior of the plasma as field free. The plasma itself is treated as an assembly of noncolliding particles which are specularly reflected at the plasma surface. The oscillating pressure of the applied field causes the plasma surface to execute a small periodic motion independent of φ and z. All other components of the displacement decay in time. Thus the plasma is positively stable against all deformations. For magnetostatic confinement this treatment yields the usual instabilities, but, in contrast to earlier work, the growth rates are bounded as the deformation wavelength approaches zero. This appears to be in better agreement with experiment.