FLEXO (Flux-Limited Extended-MHD Ohm's Law) is a multi-physics extendedmagnetohydrodynamics (MHD) discontinuous Galerkin code being developed at Sandia National Laboratories for modeling high-energy-density (HED) plasma in a pulsed-power device [1]. We present recent results from simulations of a flyer plate typical of those used in dynamic compression experiments. A beryllium flyer is compressed and accelerated by an electromagnetic drive, and comparisons are made to existing simulation and experimental results. We examine sensitivity of flyer velocities, burn-through times, and other properties to the tabular conductivity model being used, where a set of conductivity tables has been generated using a Bayesian inference scheme [2], and we compare the sensitivities in FLEXO to those seen in existing MHD simulation results.

An extended-MHD model, interfaced with tabular equation-of-state and conductivity models, has been developed in PERSEUS (Physics as an Extended-MHD Relaxation System with an Efficient Upwind Scheme) for simulating a plasma-vacuum interface under experimentally-relevant conditions for a pulsed-power system, and with minimal sensitivity to parameters characterizing the numerical vacuum. For several test problems, we demonstrate convergence of this model for sufficiently low density floors and with respect to certain vacuum parameters. This capability is crucial for predictively modeling the coupling of energy and current onto a target in a pulsed-power system.

This report describes the high-level accomplishments from the Plasma Science and Engineering Grand Challenge LDRD at Sandia National Laboratories. The Laboratory has a need to demonstrate predictive capabilities to model plasma phenomena in order to rapidly accelerate engineering development in several mission areas. The purpose of this Grand Challenge LDRD was to advance the fundamental models, methods, and algorithms along with supporting electrode science foundation to enable a revolutionary shift towards predictive plasma engineering design principles. This project integrated the SNL knowledge base in computer science, plasma physics, materials science, applied mathematics, and relevant application engineering to establish new cross-laboratory collaborations on these topics. As an initial exemplar, this project focused efforts on improving multi-scale modeling capabilities that are utilized to predict the electrical power delivery on large-scale pulsed power accelerators. Specifically, this LDRD was structured into three primary research thrusts that, when integrated, enable complex simulations of these devices: (1) the exploration of multi-scale models describing the desorption of contaminants from pulsed power electrodes, (2) the development of improved algorithms and code technologies to treat the multi-physics phenomena required to predict device performance, and (3) the creation of a rigorous verification and validation infrastructure to evaluate the codes and models across a range of challenge problems. These components were integrated into initial demonstrations of the largest simulations of multi-level vacuum power flow completed to-date, executed on the leading HPC computing machines available in the NNSA complex today. These preliminary studies indicate relevant pulsed power engineering design simulations can now be completed in (of order) several days, a significant improvement over pre-LDRD levels of performance.

helical pitch angle of the MRTI even when other proposed helical seeding mechanisms are either not present in the experiments or not accounted for in the simulations. For example, this mechanism does not require low-density power-feed plasmas to be swept in from large radius or the development of electrothermal instabilities. The Hall Instability is, thus, a new, independent explanation for the origin of the helical instabilities observed in axially premagnetized liner experiments. Simulation results supporting this mechanism are presented.

Submitted for the DPP19 Meeting of The American Physical Society Hybrid fluid-kinetic models for high-energy-density plasmas1 SEAN MILLER, ERIC CYR, THOMAS GARDINER, MATTHEW BETTENCOURT, NATHANIEL HAMLIN, KRISTIAN BECKWITH, SIDNEY SHIELDS, Sandia National Lab — Plasma physics in the high-energy-density regime can be dominated by collisional interactions between particles. Particle-in-cell (PIC) based kinetic representations have classically been used to represent these systems in rarefied regimes, however as the density of the plasma increases or a neutral gas is introduced the computational costs of particle methods increase. The goal of this research is to develop hybrid representations where the addition of continuum fluid components to the particle solve reduces runtimes in dense plasma simulations while retaining physical accuracy in rarefied regimes. Two approaches will be presented: (1) a species-based coupling where each species is represented by a different discretization (e.g. PIC ions with fluid electrons/neutrals), and (2) a PIC discretization is used to close the fluid model commonly known as a delta-f method. The current state of our implementation will be presented and the benefits and challenges of these approaches will be discussed. 1Sandia National Labs is managed and operated by National Technology Engineering Solutions of Sandia, LLC, a subsidiary of Honeywell International, Inc., for the U.S Dept. of Energys National Nuclear Security Administration under contract DE-NA0003525. Sean Miller Sandia National Lab Date submitted: 02 Jul 2019 Electronic form version 1.4