Limitation of accelerating process in the partly neutralized relativistic electron hollow beam

Abstract

A fluid-Maxwell thoery of the diocotron instability is developed for a relativistic electron hollow beam which is assumed in rigid-rotor and cold laminar flow equilibria. Stability analysis is performed for a sharp boundary electron density profile including the influence of positive ions which can accumulate in a long pulse device, and which form a partially neutralizing background. In the case of the strong magnetic field and tenuous electron beam (plasma frequency ωpb ≪gyrofrequency ωc) a partially neutralizing ion background staying uniformly within the beam annulus (R1<r<R2) has a stabilizing effect on the diocotron instability, R1 and R2 are the inner and outer radius of the annular hollow beam, respectively. However, the ions accumulating in the center of the beam (0<r<R1) have a destabilizing effect on the diocotron instability. Most importantly the kink mode becomes unstable with a growth rate several tenths of the diocotron frequency ωD ≡ ω2pb/2γ2ωc, where γ is the relativistic scaling factor.

The influence of azimuthal motion on ion resonance instability for a non-neutral plasma column

“…Ions are commonly produced from the residual gas in the apparatus. Without taking ion dynamics into account, the fractional charge neutralization / has a strong stabilizing influence on stability behaviour (Chen 1984), particularly in relativistic electron beams. Nevertheless, when the ion dynamics is considered, because of the angular rotational shear of the plasma column, surface waves of electrons and ions propagate relative to one another.…”