Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session UM9: Mini-conference on the Crossover between High Energy Density Plasmas and Ultracold Neutral Plasmas: II |
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Chair: Jacob Roberts, Colorado State University Room: OCC C123 |
Thursday, November 8, 2018 2:00PM - 2:20PM |
UM9.00001: The High Energy Density Science Center: From Warm Dense to Hot Dense Matter Frank R Graziani The mission of the High Energy Density Science Center is to strengthen fundamental research collaborations in the field of high energy density science (HEDS) between Lawrence Livermore National Laboratory (LLNL) and the academic community. Our approach includes four pillars of action: Building Bridges with the HEDS Community Developing Educational/Training Programs to Advance Knowledge Fostering Research that Strengthens Core Technical Competencies Addressing HEDS Challenges Impacting LLNL Missions We will discuss the various activities associated with the Center, including educational programs for graduate students and staff. We will also discuss new and on-going collaborative experimental and computational research in such varied fields as pressure ionization in dense plasmas, kinetic theory, relativistic shocks, hydrodynamic instabilities, alternative ignition designs. Finally, we will look to the future and the role that ultra-cold plasmas play in our research portfolio. |
Thursday, November 8, 2018 2:20PM - 2:40PM |
UM9.00002: X-Ray Diffraction of Ramp-Compressed Sodium Danae Polsin, Thomas Boehly, Gilbert W Collins, James R Rygg, Xuchen Gong, Jon Henry Eggert, Amy Jenei, Malcolm I McMahon Extreme compression can alter the free-electron behavior of “simple” metals such as sodium. At pressures greater than 200 GPa, Na is predicted to transform into a transparent electride structure where valence electrons are localized in interstitial regions. Laser-driven ramp compression is used to compress Na into this unexplored pressure regime to investigate the crystal structure, optical properties, and melting behavior of Na. X-ray diffraction is used to constrain the crystal structure and detect melting. Optical reflectivity measurements are used to detect metal-insulator transitions and simultaneous velocimetry is used to infer the Na pressure. We show the highest‑pressure solid x-ray diffraction and reflectivity data on Na to date. |
Thursday, November 8, 2018 2:40PM - 3:00PM |
UM9.00003: Laser Cooled Neutral Plasmas: A Laboratory for the Study of Strongly Coupled Systems Thomas Killian, Thomas Langin, Grant M Gorman Strong coupling arises when interaction energies are comparable to, or exceed, kinetic energies, and this occurs in diverse systems such as white dwarf stars, strongly correlated electron systems, and cold quantum gases. Ultracold neutral plasmas (UNPs), generated by photoionization of a laser-cooled gas, are a powerful platform for studying the physics of strongly coupled Yukawa plasmas. I will briefly describe experimental studies of self-diffusion and thermal equilibration, and describe the role of strong coupling in these phenomena. I will also present results from the first application of laser-cooling to a neutral plasma. Through laser-cooling we have created plasmas with ion temperatures as low as 50 mK and achieved a factor of 4 enhancement in the coupling strength to \Gamma=11, allowing for experimental benchmarking of new models and molecular dynamics simulations of transport across a range of coupling strength. |
Thursday, November 8, 2018 3:00PM - 3:20PM |
UM9.00004: Charged Particle Transport in Non-Ideal Plasmas Liam G Stanton, Michael Sean Murillo Coulomb collisional processes in plasmas occur in many scenarios, ranging from particle and energy transport to wave damping, particulate drag, wake formation, and others. The theoretical description of these processes can be particularly challenging for plasmas, as the long range interactions preclude the use of simplifying approximations such as neglecting many-body effects, which are particularly important for non-ideal plasmas, such as dense plasmas found in inertial confinement fusion (ICF) experiments and ultra-cold neutral plasmas (UCP). We have developed a simplified effective potential approach within a Boltzmann-type framework that yields accurate and computationally efficient fits for all of the relevant cross sections and collision integrals needed to construct transport coefficients. Our results, which span the UCP to ICF regimes, have been validated with molecular dynamics simulations for self-diffusion, interdiffusion, viscosity, thermal conductivity and stopping power. Molecular dynamics has also been used to examine the underlying assumptions of this Boltzmann approach through a categorization of behaviors of the velocity autocorrelation function in the Yukawa phase diagram. |
Thursday, November 8, 2018 3:20PM - 3:40PM |
UM9.00005: Theory for Ion Transport in Ultracold and High Energy Density Plasmas Scott D Baalrud, Jerome Daligault, Charles Starrett, Didier Saumon This talk will review a recent example where synergies between ultracold neutral plasmas (UNPs) and high energy density plasmas (HEDP) were used to advance both fields. A common challenge is to understand how strong Coulomb coupling of ions influences transport properties in a neutral plasma. We recently developed a theory (EPT) that extends Landau-Spitzer theory into the strongly coupled regime [1]. It uses the radial distribution function as input. The theory was tested in UNP experiments [2], and found to accurately predict ion transport coefficients. It was later applied to HEDP systems by using a model for the ion radial distribution function that accounts for degenerate electrons in dense plasmas [3]. The predictions were tested over a variety of conditions relevant to HEDP experiments using quantum molecular dynamics simulations [4]. Similar good agreement was found. This illustrates an example where knowledge gained from tabletop UCP experiments directly advanced understanding of dense HED plasmas. [1] Baalrud and Daligault, PRL 110, 235001 (2013). [2] Strickler, et al, PRX 6, 021021 (2016). [3] Starrett and Saumon, PRE 87, 013104 (2013). [4] Daligault, et al., PRL 116, 075002 (2016). |
Thursday, November 8, 2018 3:40PM - 4:00PM |
UM9.00006: Phase-Space Dynamics of Sculpted Ultracold Neutral Plasmas. Vikram Dharodi, Michael Sean Murillo Through a series of molecular dynamics simulations we have explored the non-equilibrium dynamics of heterogeneous non-ideal plasmas formed with spatially modulated ionizing radiation. We have developed a computational model for such sculpted ultracold neutral (SUN) plasmas formed by ionizing an ultracold neutral gas. We model ion dynamics through a screened Coulomb interaction in which the screening length varies according to the dynamics. Ion-electron and ion-neutral collisions are modeled though Langevin forces, allowing us to examine the role of heating or cooling due to background species. We constructed a hydrodynamic model for SUN plasmas and compute its field quantities (density, flow velocity and temperature) in the molecular dynamics simulations, included examining the accuracy of a local-equilibrium closure. We have examined these quantities and others, such as the spatial Coulomb coupling parameter, in three geometries, including a double slab, a solid rod and a hollow rod. Our results suggest that a wealth of plasma physics can be explored with SUN plasmas; however, we also discuss where further improvements to our computational tools are warranted for future studies. |
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