Sculpted ultracold neutral plasmas.

Vikram S Dharodi,Michael S Murillo

doi:10.1103/physreve.101.023207

Abstract

Ultracold neutral plasma (UNP) experiments allow for careful control of plasma properties across Coulomb coupling regimes. Here, we examine how UNPs can be used to study heterogeneous, nonequilibrium phenomena, including nonlinear waves, transport, hydrodynamics, kinetics, stopping power, and instabilities. Through a series of molecular dynamics simulations, we have explored UNPs formed with spatially modulated ionizing radiation. We have developed a computational model for such sculpted UNPs that includes an ionic screened Coulomb interaction with a spatiotemporal screening length, and Langevin-based spatial ion-electron and ion-neutral collisions. We have also developed a hydrodynamics model and have extracted its field quantities (density, flow velocity, and temperature) from the molecular dynamics simulation data, allowing us to investigate kinetics by examining moment ratios and phase-space dynamics; we find that it is possible to create UNPs that vary from nearly perfect fluids (Euler limit) to highly kinetic plasmas. We have examined plasmas in three geometries: a solid rod, a hollow rod, and a gapped slab; we have studied basic properties of these plasmas, including the spatial Coulomb coupling parameter. By varying the initial conditions, we find that we can design experimental plasmas that would allow the exploration of a wide range of phenomena, including shock and blast waves, stopping power, two-stream instabilities, and much more. Using an evaporative cooling geometry, our results suggest that much larger Coulomb couplings can be achieved, possibly in excess of 10.

Highlights

Knowledge of the physics of nonideal plasmas [1] is important both at a fundamental level, to understand how correlations and collisions impact plasma properties, and for a wide range of applications, including astrophysics [1,2,3], pulsed power [4,5,6], inertially confined plasmas [7], and laserexcited solids [8,9,10,11,12], among other applications
Molecular dynamics (MD), and we use an electronic energy equation that accounts for electronic temperature changes arising from those variations. With this model of Ultracold neutral plasma (UNP), we explore the physics of hydrodynamics, including the perfectfluid limit, as well as kinetic processes associated with beams, such as stopping power and two-stream instabilities; we explore these processes in the contexts of three different initial density distributions
We turn to the nonequilibrium molecular dynamics (NEMD) computational procedure for studying sculpted ultracold neutral plasmas (SUNPs) and present the results of our studies

Summary

Introduction

Knowledge of the physics of nonideal plasmas [1] is important both at a fundamental level, to understand how correlations and collisions impact plasma properties, and for a wide range of applications, including astrophysics [1,2,3], pulsed power [4,5,6], inertially confined plasmas [7], and laserexcited solids [8,9,10,11,12], among other applications. The plasma properties that have been studied are primarily relevant for macroscopically homogeneous and isotropic plasmas, whereas real plasmas tend to have important density gradients and transient behavior, as in the cases of implosion dynamics in inertial-confinement fusion experiments [20] and of shocks and instabilities [21,22], in general.

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