The Instability of an Annular Electron Beam Propagating along a Guided Magnetic Field

Abstract

The instabilities of an infinitely long and azimuthally symmetric annular electron beam propagating along an external applied magnetic field are investigated using the fluid-Maxwell theory. Unlike the treatment in the conventional diocotron instability, full electromagnetic perturbations have been emphasized and no approximation has been made such as k& <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">#x02016;</sub> ~ 0 and ω ~ckß in the macroscopic cold fluid description. There have been found two distinct and different instabilities depending on the value of doppler-shifted eigenfrequency ω-ckß. The diocotron instability dominates in the low frequency region while cyclotron resonance perturbation plays a major role in the high frequency domain. In the case of a sharp boundary density profile, the growth rates versus different wavenumber k are shown for both instabilities in the beam parameters of out interest.