Expansion Dynamics of Cold Non-Neutral Plasma

TL;DR

This paper investigates the expansion behavior of cold, strongly coupled non-neutral plasma in different density regimes, revealing shock fronts, focusing effects, and ion correlations through experiments and simulations.

Contribution

It provides new experimental observations of plasma shock fronts, focusing, and ion correlations in cold non-neutral plasma, supported by simulation validation.

Findings

Observation of plasma shock fronts in high-density regime

Detection of plasma focusing effects due to external fields

Development of ion correlations and asymmetries in low-density regime

Abstract

We study the expansion of a strongly coupled, non-neutral, and cylindrically arranged ion plasma into the vacuum. The plasma is made from cold rubidium atoms in a magneto-optical trap (MOT) and is formed via ultraviolet photoionization. Higher-density and lower-density plasmas are studied to exhibit different aspects indicative of strong coupling. In a higher-density regime, we report on the formation and persistence of plasma shock fronts, as well as external-field-induced plasma focusing effects. In the lower-density regime, conditions are ideal to observe the development and evolution of nearest-neighbor ion correlations, as well as geometry-induced asymmetries in the pair correlation function. Simulated results from a trajectory model and a fluid model are in good agreement with the measurements.