Diocotron instability of an intense relativistic electron beam in an accelerator.

Abstract

A high-current annular electron beam in an accelerator is subject to various instabilities. A general fluid-Maxwell theory of the diocotron instability is developed for an infinitely long and azimuthally symmetric annular electron beam propagating along an external magnetic field. In contrast with the treatment used in the conventional diocotron instability, the assumptions of tenuous electron beam and strong magnetic field have been eliminated. Furthermore, the restriction of infinite axial wavelength perturbation has been removed and the approximation of \ensuremath{\omega}\ensuremath{\sim}ck\ensuremath{\beta} is no longer applied. Instead, we conduct full electromagnetic perturbation in the macroscopic cold-fluid description of plasma dynamics with the beam parameters of general interest. In the special case of a sharp-boundary density profile, the diocotron instability which dominates in the low-frequency region is investigated in a broad range of beam parameters and geometries. The results are significantly different from that obtained from the conventional diocotron instability; the kink mode can be destabilized and the growth rates are much larger for every azimuthal mode.