# Experimental Observation of Electron-Acoustic Wave Propagation in Laboratory Plasma

## TL;DR

This paper reports the first laboratory observation of electron-acoustic waves propagating with phase velocity about 1.8 times the electron thermal velocity, facilitated by cold electron drift reducing damping effects.

## Contribution

It demonstrates experimental detection of electron-acoustic waves in a laboratory plasma and shows how cold electron drift can enable their propagation despite damping.

## Key findings

- Electron-acoustic waves observed with phase velocity ~1.8 times electron thermal velocity.
- Cold electron drift reduces damping and allows wave growth.
- Experimental results agree with theoretical predictions.

## Abstract

In the field of fundamental plasma waves, direct observation of electron-acoustic wave (EAW) propagation in laboratory plasmas remains a challenging problem, mainly because of heavy damping. In the MaPLE device, the wave is observed and seen to propagate with phase velocity $\sim1.8$ times the electron thermal velocity. A small amount of cold, drifting electrons, with moderate bulk to cold temperature ratio ($\approx 2 - 3$), is present in the device. It plays a crucial role in reducing the damping. Our calculation reveals that the drift relaxes the stringent condition on the temperature ratio for wave destabilization. Growth rate becomes positive above a certain drift velocity even if the temperature ratio is moderate. The observed phase velocity agrees well with the theoretical estimate. Experimental realization of the mode may open up a new avenue in EAW research.