# Generation of forerunner electron beam during interaction of ion beam pulse with plasma

## TL;DR

This study uses large-scale simulations to analyze the evolution of two-stream instability in ion beam-plasma interactions, revealing the formation of a forerunner electron beam and subsequent nonlinear dynamics.

## Contribution

It provides a detailed, stage-by-stage analysis of the instability process, including the formation of a forerunner electron beam during ion beam propagation through plasma.

## Key findings

- Formation of a forerunner electron beam ahead of the ion pulse.
- Secondary two-stream instability causes upstream plasma preheating.
- Ion trapping leads to nonlinear beam ion heating and instability cessation.

## Abstract

The long-time evolution of the two-stream instability of a cold ion beam pulse propagating though the background plasma is investigated using a large-scale one-dimensional electrostatic kinetic simulation. The three stages of the instability are identified and investigated in detail. After the initial linear growth and saturation by the electron trapping, a portion of the initially trapped electrons becomes detrapped and moves ahead of the ion beam pulse forming a {forerunner} electron beam, which causes a secondary two-stream instability that preheats the upstream plasma electrons. Consequently, the self-consistent nonlinear-driven turbulent state is set up at the head of the ion beam pulse with the saturated plasma wave sustained by the influx of the cold electrons from the upstream of the beam that lasts until the final stage when the beam ions become trapped by the plasma wave. The beam ion trapping leads to the nonlinear heating of the beam ions that eventually extinguishes the instability.