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

Area of Science:

• Plasma Physics
• Astrophysics
• Laser-Plasma Interactions

Background:

• Electrostatic two-stream instabilities are vital for collisionless shock formation, driving ion heating and acceleration.
• Precise identification of these instabilities is crucial as they influence the number and energy of shock-accelerated ions.

Purpose of the Study:

• To identify the specific electrostatic instabilities driving ion acceleration in a multicomponent plasma during collisionless shock formation.
• To analyze the role of ion velocity differences in exciting these instabilities.

Main Methods:

• Two-dimensional particle-in-cell simulations of multicomponent plasma.
• Linear analysis using a one-dimensional electrostatic plasma dispersion function, incorporating electron and ion temperature effects.

Main Results:

• Simulations revealed ion reflection, acceleration, and the excitation of a longitudinally propagating electrostatic instability.
• Linear analysis identified the electrostatic ion-beam two-stream instability (IBTI) as the most unstable mode, driven by velocity differences between protons and carbon ions.
• A weaker electrostatic electron-ion two-stream instability was observed, associated with reflected protons.

Conclusions:

• The fast-growing IBTI, excited by velocity differences in laser-driven collisionless shocks, significantly enhances the brightness of quasimonoenergetic ion beams.
• IBTI's weak dependence on electrons highlights its primary role in ion acceleration mechanisms within these shocks.