Nathaniel Donald Hamlin

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.

We identify the time-dependent physics responsible for the critical reduction of current losses in magnetically insulated transmission lines (MITLs) due to uninsulated space charge-limited currents of electrons emitted by field stress. A drive current of sufficiently short pulse length introduces a strong enough time dependence that steady-state results alone become inadequate for the complete understanding of current losses. The time-dependent physics can be described as a nonlocal, diamagnetic electromagnetic response of space charge limited currents. As the pulse length is increased or equivalently, the MITL length reduced, these time-dependent effects diminish and current losses converge to those predicted by the well-known Child–Langmuir law in the external (vacuum) fields. We present a simple one-dimensional (1D) model that encapsulates the essence of this physics. We find excellent agreement with 2D particle-in-cell simulations for two MITL geometries, Cartesian parallel plate and azimuthally symmetric straight coaxial. Based on the 1D model, we explore various scaling dependencies of MITL losses with relevant parameters, e.g., peak current, pulse length, geometrical dimensions, etc. We propose an improved physics model of magnetic insulation in the form of a Hull curve, which could also help improve predictions of current losses by common circuit element codes, such as BERTHA. Finally, we describe how to calculate the temperature rise due to electron impact within the 1D model.

• FLEXO (Flux-Limited Extended-MHD Ohm's Law) is a production-line extended-magnetohydrodynamics (MHD) code being developed at Sandia National Laboratories for modeling high-energy-density (HED) plasma in a pulsed-power device, primarily with applications to the study of inertial confinement fusion (ICF). Results are presented from various verification and validation tests of extended-MHD and multi-material modeling capabilities.

Magnetized liner inertial fusion (MagLIF) is a magneto-inertial-fusion concept that is studied on the 20-MA, 100-ns rise time Z Pulsed Power Facility at Sandia National Laboratories. Given the relative success of the platform, there is a wide interest in studying the scaled performance of this concept at a next-generation pulsed-power facility that may produce peak currents upward of 60 MA. An important aspect that requires more research is the instability dynamics of the imploding MagLIF liner, specifically how instabilities are initially seeded. It has been shown in magnetized 1-MA thin-foil liner Z-pinch implosion simulations that a Hall interchange instability (HII) effect [J. M. Woolstrum et al., Phys. Plasmas 29, 122701 (2022)] can provide an independent seeding mechanism for helical magneto-Rayleigh–Taylor instabilities. In this paper, we explore this instability at higher peak currents for MagLIF using 2D discontinuous Galerkin PERSEUS simulations, an extended magneto-hydrodynamics code [C. E. Seyler and M. R. Martin, Phys. Plasmas 18, 012703 (2011)], which includes Hall physics. Our simulations of scaled MagLIF loads show that the growth rate of the HII is invariant to the peak current, suggesting that studies at 20-MA are directly relevant to 60-MA class machines.