Sculpted ultracold neutral plasmas

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.

Ring structural transitions in strongly coupled dusty plasmas

“…shown for sculpted ultracold neutral plasmas in [55]. Since the transition from a ring monolayer to a cylindrical shell structure is highly sensitive to the dust interaction potential, we further conjecture that it can be used to investigate the dust particle charging in laboratory settings.…”

Expansion of Ultracold Neutral Plasmas with Exponentially Decaying Density Distributions

“…It would be informative to compare the observations described here with two-component MD codes with open boundary conditions 71 and recently developed tools for describing heterogeneous, non-equilibrium plasmas subject to effects of strong coupling. 72 This would provide validation of numerical methods and additional insight into some aspects of the expansion of the exponential plasma, such as electron temperature evolution and the influence of Coulomb-explosion effects on ion temperature near the plasma center. Further study is also needed to explore the possible formation of shock waves associated with the extrema in the velocity transects and steepening of the density gradient.…”

Sarkas: A Fast Pure-Python Molecular Dynamics Suite for Plasma Physics

“…In contrast, the field of computational plasma physics has traditionally relied on hydrodynamics [5,6] and kinetic [7,8] codes because the temporal and spatial scales of interest are much too large for MD to be tractable; moreover, the detailed description of discrete particles is less important and instead macroscopic field variables are computed. However, MD plays a central role in a diverse set of plasma subfields concerned with understanding microscopic particles such as astrophysical systems [9,10], dusty plasmas [11,12], ultracold neutral plasmas [13,14], dense plasmas [15,16], low temperature plasmas [17,18], plasma beams [19,20], quark-gluon plasmas [21,22], etc.…”