Temperature Relaxation in Strongly-Coupled Binary Ionic Mixtures

Luciano G Silvestri,R Tucker Sprenkle,Michael S Murillo,Scott D Bergeson

doi:10.1109/icops36761.2021.9588497

Luciano G Silvestri, R Tucker Sprenkle + Show 2 more

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https://doi.org/10.1109/icops36761.2021.9588497

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Abstract

Relaxation in non-ideal plasmas is a complex process that involves expansions/contractions, thermal conduction, thermalization and temperature equilibration. Unfortunately, very little is known experimentally about these processes because of the challenges associated with isolating them individually. As such, we rely heavily on unvalidated theoretical models. This knowledge gap is particularly large for the very challenging case of ionic relaxation. Current improvements in experimental techniques now allow for the creation of ultracold binary mixtures for the investigation of equilibrium relaxation phenomena dominated by ion-ion collisions. These experiments, when complemented by large-scale molecular dynamics (MD) simulations, promise to provide detailed data on these processes. We have modeled a binary relaxing ultracold neutral plasma with MD, motivated by experiments at Brigham Young University, and compared the results to the most common theoretical models. None of the temperature relaxation rates from current theoretical models is within an order of magnitude of the MD simulations, suggesting serious gaps in our knowledge of ionic relaxation. We argue that such disagreement is due to dynamical correlations neglected by the currently available theoretical models 1 , 2 .

Highlights

Advancing the frontier of dense plasma science requires a deep understanding of plasma processes in extreme conditions
In this paper we report the first measurements of the ion-ion temperature relaxation rate using a strongly-coupled dual-species ultracold neutral plasmas (UNPs) [46]
We show that within the experimental uncertainties, the measured temperature relaxation rates match the results of classical molecular dynamics (MD) simulations

Summary

Introduction

Advancing the frontier of dense plasma science requires a deep understanding of plasma processes in extreme conditions. Dense plasma models must include effects of Fermi degeneracy [19], atomic physics [24], and strong scattering [25]. Temperature relaxation has been studied extensively for electron-ion systems [19,20,25,26,27,28,36,37,38,39] and plasma theories are tailored for the case of disparate mass. Recent laboratory experiments have shown ultracold neutral plasmas (UNPs) to be effective HEDP simulators over a limited range of parameters [11, 43,44,45,46,47,48,49,50].

Results

Conclusion