Stability of relativistic electron beaj1s in density channels-I

We have conducted a theoretical and computational study of electron beam stability in density channels whose radii are comparable with the pinched beam radius. The principal instabilities of interest are the resistive hose, which has been treated by the multi-component code VIPER and particle simulation code SIMM1, and the axisymmetric hollowing instability, which has been treated by the particle simulation code SLMMO. If beam and channel properties are chosen so that the peak E/p is ∼10² kV/cm-atm, then avalanche breakdown will be a strong function of radial distance r. For the usual case in which the channel density has an on-axis minimum (simple channel), avalanche ionization may increase return current flow inside the beam and strongly enhance both instabilities. If an annular channel is produced, however, avalanche may cause most of the return current to flow outside the beam, thus enhancing beam stability. Model calculations for both types of channels will be compared with recent experiments on beams propagating in laser-produced channels.