Propagation of High Current Relativistic Electron Beams

Abstract

Theoretical self-consistent relativistic electron beam models are developed which allow the propagation of relativistic electron fluxes in excess of the Alfven-La.wson critical-current limit for a fully neutralized beam. Development of a simple, fully relativistic, self-consistent equilibrium is described which can carry arbitrarily large currents at or near complete electrostatic neutralization. A discussion of a model for magnetic neutralization is presented wherein it is shown that large numbers of electrons from a background plasma are counterstreaming slowly within the beam so that the net current density in the system, and therefore, the magnetic field, is nearly zero. A solution of an initial-value problem for a beam-plasma system is given which indicates that magnetic neutralization can be expected to occur for plasma densities that a.re large compared with beam densities. It is found that the application of a strong axial magnetic field to a uniform beam allows propagation regardless of the magnitude of the beam current. Some comparisons are made with recent experimental data.

Multidimensional electron beam-plasma instabilities in the relativistic regime

“…The tenuous beam electrons are channeled into beams, which are immersed in the almost uniform background of the electrons of the dense beam. Such current filaments can be remarkably stable, 189 which has been confirmed with PIC simulations. 51,58 Further magnetic pinching of the beam electrons produces a strong electric field accelerating the ions in the radial direction.…”

Estimates of dense plasma heating by stable intense electron beams

“…When co,a/c >> 1 (a = beam radius), this region is just the relativistic beam region* (HAMMER and ROSTOKER, 1970). The dependence of the anomalous resistivity 7 (or equivalently, of vS) on U and U is in considerable dispute (for a review, see SELF, 1970).…”

“…The return current will be spatially restricted to the beam channel if o,2a2/c2 > 1 (U, is the background electron plasma frequency) (HAMMER and ROSTOKER, 1970). Ordinarily the plasma density np must exceed the beam density n,-1012-lQ13 by at least an order of magnitude.…”

Status and Prospects of the Fast Ignition Inertial Fusion Concept

“…At this limit the self generated B field makes the Larmor radius smaller than the beam diameter and stops the beam propagation. Hot electrons entering the dense plasma are initially 100% compensated by a return current of background electrons 35 . The finite resistivity to the return current sets up an Ohmic E field which slows and can reflect the hot electrons.…”