Interaction of a high intensity short pulse-width relativistic electron beam with plasma

Abstract

The interaction of a high intensity relativistic electron beam with plasma is studied using a short pulsewidth electron beam source. The beam is injected axially into a magnetized plasma column with density np=4*1011-1*1013 cm-3. The beam current is completely neutralized by a 'reverse current' when the plasma density is sufficiently high. In a low density region decay of the reverse current appears, explained by enhanced collisions due to plasma instabilities. Though the pulsewidth is as short as 3 ns, the beam energy is efficiently transferred and the plasma is heated. Dependence of plasma energy increment upon initial plasma density and beam current are studied. As a result of the beam-plasma interaction, strong microwave emissions are observed at frequencies near electron cyclotron harmonics that last long after the termination of the beam, and the fundamental emissions are very weak. A possible explanation is to attribute the microwave emissions to electrostatic cyclotron harmonic wave instabilities excited in non-Maxwellian plasma heated by the electron beam and trapped in the magnetic field.