2-D studies of Relativistic electron beam plasma instabilities in an inhomogeneous plasma

TL;DR

This paper investigates how inhomogeneous plasma can suppress relativistic electron beam instabilities, using analytical methods and 2-D Particle-In-Cell simulations, revealing reduced growth rates and current channelization.

Contribution

It provides the first detailed analytical and simulation study showing inhomogeneous plasma density reduces instability growth in relativistic electron beams.

Findings

Inhomogeneous plasma density decreases dominant instability growth rates.

Current channelization occurs in inhomogeneous plasma conditions.

Scale length of inhomogeneity less than plasma skin depth is critical.

Abstract

Relativistic electron beam propagation in plasma is fraught with several micro instabilities like two stream, filamentation etc., in plasma. This results in severe limitation of the electron transport through a plasma medium. Recently, however, there has been an experimental demonstration of improved transport of Mega Ampere of electron currents (generated by the interaction of intense laser with solid target) in a carbon nanotube structured solid target [Phys. Rev Letts. 108, 235005 (2012)]. This then suggests that the inhomogeneous plasma (created by the ionization of carbon nano tube structured target) helps in containing the growth of the beam plasma instabilities. This manuscript addresses this issue with the help of a detailed analytical study and simulations with the help of 2-D Particle - In - Cell code. The study conclusively demonstrates that the growth rate of the dominant instability in the 2-D geometry decreases when the plasma density is chosen to be inhomogeneous, provided the scale length 1/ks of the inhomogeneous plasma is less than the typical plasma skin depth (c/{\omega}p0 ) scale. At such small scale lengths channelization of currents are also observed in simulation.