Observations of a Field-Aligned Ion/Ion-Beam Instability in a Magnetized Laboratory Plasma

TL;DR

This study experimentally observes a field-aligned ion/ion-beam instability, specifically the resonant right hand instability (RHI), in a laboratory plasma, providing insights into collisionless plasma coupling relevant to shock formation.

Contribution

The paper introduces a novel experimental setup using high-energy lasers to generate super-Alfvénic debris plasma and directly observes the RHI in a controlled laboratory environment.

Findings

Detection of super-Alfvénic debris ions exciting RHI

Magnetic flux probes observed right-hand circular polarization

Measurements agree with 2D hybrid simulations

Abstract

Collisionless coupling between super Alfv\'{e}nic ions and an ambient plasma parallel to a background magnetic field is mediated by a set of electromagnetic ion/ion-beam instabilities including the resonant right hand instability (RHI). To study this coupling and its role in parallel shock formation, a new experimental configuration at the University of California, Los Angeles utilizes high-energy and high-repetition-rate lasers to create a super-Alfv\'{e}nic field-aligned debris plasma within an ambient plasma in the Large Plasma Device (LAPD). We used a time-resolved fluorescence monochromator and an array of Langmuir probes to characterize the laser plasma velocity distribution and density. The debris ions were observed to be sufficiently super-Alfv\'{e}nic and dense to excite the RHI. Measurements with magnetic flux probes exhibited a right-hand circularly polarized frequency chirp consistent with the excitation of the RHI near the laser target. We compared measurements to 2D hybrid simulations of the experiment.