High-current fast electron beam propagation in a gas

Abstract

Propagation of high-current relativistic electron beam in a gas has been studied experimentally in [1] in connection with the fast ignition concept of the inertial confinement fusion. In this paper, our numerical code based on the Particle-in-Cell method is utilized to simulate the electron beam propagation under the conditions similar to those of the experiment [1]. Our results demonstrate generation of a strong electrostatic field at the surface of the target from which the beam enters into the gas. The strength of this field depends in particular on the density of the gas and the field may reflect a significant part of the beam back into the target and decelerate the propagating beam. Ionization of the gas is provided by the electric field created by a dense bunch of runaway electrons and the ionization front may propagate with the velocity close to the velocity of light until the runaway bunch is depleted.