Identification of electrostatic two-stream instabilities associated with a laser-driven collisionless shock in a multicomponent plasma

TL;DR

This study uses simulations and linear analysis to identify the dominant electrostatic two-stream instabilities in laser-driven collisionless shocks within multicomponent plasmas, revealing their role in ion acceleration.

Contribution

It provides a detailed identification of the ion-beam two-stream instability as the primary mechanism in such shocks, including its dependence on plasma components and temperature effects.

Findings

Ion reflection and acceleration observed at shock front

Ion-beam two-stream instability identified as dominant

Enhanced ion beam brightness due to IBTI excitation

Abstract

Electrostatic two-stream instabilities play essential roles in an electrostatic collisionless shock formation. They are a key dissipation mechanism and result in ion heating and acceleration. Since the number and energy of the shock-accelerated ions depend on the instabilities, precise identification of the active instabilities is important. Two-dimensional particle-in-cell simulations in a multicomponent plasma reveal ion reflection and acceleration at the shock front, excitation of a longitudinally propagating electrostatic instability due to a non-oscillating component of the electrostatic field in the upstream region of the shock, and generation of up- and down-shifted velocity components within the expanding-ion components. A linear analysis of the instabilities for a C2H3Cl plasma using the one-dimensional electrostatic plasma dispersion function, which includes electron and ion temperature effects, shows that the most unstable mode is the electrostatic ion-beam two-stream instability (IBTI), which is weakly dependent on the existence of electrons. The IBTI is excited by velocity differences between the expanding protons and carbon-ion populations. There is an electrostatic electron-ion two-stream instability with a much smaller growth rate associated with a population of protons reflecting at the shock. The excitation of the fast-growing IBTI associated with laser-driven collisionless shock increases the brightness of a quasi-monoenergetic ion beam.