Electron Evaporation from an Ultracold Plasma in a Uniform Electric Field

TL;DR

This study investigates how a uniform electric field influences electron evaporation from an ultracold plasma, combining experimental observations with theoretical calculations to understand electron flux during plasma expansion.

Contribution

The paper introduces a model predicting electron evaporation rates in ultracold plasmas under electric fields, validated by experimental data.

Findings

Electric field increases electron evaporation rate.

Calculated electron flux matches experimental observations.

Electron cloud distribution remains Gaussian during expansion.

Abstract

Electrons in an expanding ultracold plasma are expected to be in quasi-equilibrium, since the collision times are short compared to the plasma lifetime, yet we observe electrons evaporating out as the ion density decreases during expansion. We observe that a small electric field that shifts the electron cloud with respect to the ions increases the evaporation rate. We have calculated the spatial distribution of a zero-temperature electron cloud as a function of applied field and ion density, which is assumed to be Gaussian at all times. This calculation allows us to predict the flux of cold electrons from the plasma at all times, and is in good agreement with our observed electron signal.