Laboratory measurements of electrostatic solitary structures generated by electron beam injection

TL;DR

This study reports laboratory observations of electrostatic solitary structures generated by electron beam injection, revealing their properties and potential wave mode origins in plasma physics.

Contribution

The paper provides the first laboratory measurements of electrostatic solitary structures and identifies their likely origin as electrostatic whistler mode waves.

Findings

Positive potential pulses with specific widths and velocities were measured.

Nonlinear wave packets with similar characteristics were observed.

Results suggest the structures originate from an instability driven by field-aligned currents.

Abstract

Electrostatic solitary structures are generated by injection of a suprathermal electron beam parallel to the magnetic field in a laboratory plasma. Electric microprobes with tips smaller than the Debye length ($\lambda_{De}$) enabled the measurement of positive potential pulses with half-widths 4 to 25$\lambda_{De}$ and velocities 1 to 3 times the background electron thermal speed. Nonlinear wave packets of similar velocities and scales are also observed, indicating that the two descend from the same mode which is consistent with the electrostatic whistler mode and result from an instability likely to be driven by field-aligned currents.