Plasma instabilities of a finite‐radius electron beam in a uniform plasma

Abstract

To study electromagnetic radiation induced by electron beam injection from the space shuttle, the electromagnetic dispersion equation of a finite‐radius cold electron beam in a neutralizing background was solved numerically. The numerical solutions indicate that a keV electron beam can drive the beam and whistler modes unstable, regardless of whether the beam is homogeneous or has a finite radius. Although the beam mode is excited for frequencies up to the electron plasma frequency, only waves with frequencies below the electron cyclotron frequency can propagate outside the beam. The parallel wave numbers of the whistler waves excited by the finite‐radius and the homogenous electron beams are similar, suggesting that the finite‐radius electron beam also excites the whistler waves near the resonance cone. These results are applied to explain the whistler waves radiated from the keV electron beam injected from Spacelab 2.