Ultracold Plasma Expansion as a Function of Charge Neutrality

TL;DR

This paper develops a theoretical model to analyze how the charge neutrality of ultracold plasmas influences their expansion rate and electron temperature, highlighting the importance of neutrality in experimental measurements.

Contribution

The work introduces a model that predicts the impact of charge neutrality on ultracold plasma expansion and electron temperature, emphasizing effects despite small Debye lengths.

Findings

Expansion rate depends on plasma neutrality.

Electron temperature in the interior is sensitive to neutrality.

Implications for accurate measurement of plasma properties.

Abstract

Ultracold plasmas (UCPs) are created under conditions of near but not perfect neutrality. In the limit of zero electron temperature, electron screening results in non-neutrality manifesting itself as an interior region of the UCP with both electrons and ions and an exterior region composed primarily of ions. The interior region is the region of the most scientific interest for 2-component ultracold plasma physics. This work presents a theoretical model through which the time evolution of non-neutral UCPs is calculated. Despite Debye screening lengths much smaller than the characteristic plasma spatial size, model calculations predict that the expansion rate and the electron temperature of the UCP interior is sensitive to the neutrality of the UCP. The predicted UCP dependence on neutrality has implications for the correct measurement of several UCP properties, such as electron temperature, and a proper understanding of evaporative cooling of the electrons in the UCP.