Numerical Simulations of Thick-Aluminum-Wire Behavior Under Megaampere-Current Drive

Abstract

A series of experiments to study the behavior of thick wires (0.5-2 mm in diameter) driven by currents of about 1 MA has recently been conducted on the Zebra facility at the University of Nevada, Reno. The objective of these experiments was to study plasma formation on the surface of conductors under the influence of megagauss magnetic fields. Laser shadowgraphy, filtered optical and extreme ultraviolet photodiodes, and extreme ultraviolet spectroscopy used in the experiments provided data on radial expansion of wires and on plasma radiation. This paper focuses on numerical simulations of these experiments. Simulations with wires having diameters up to 1.6 mm demonstrated plasma formation with temperatures above 3 eV, which is in preliminary agreement with the experiment. For 2-mm-diameter wires, although plasma can be observed in the simulations, it has substantially smaller optical thickness than in the simulations of the smaller diameter wires, and the radiation fluxes prove to be much lower. This can shed light on the experimental results where the radiation of the 2-mm wires was very weak. The simulated time dependences of the wire radii agree rather well with the experimental results obtained using laser diagnostics and visible-light imaging. The experimental data of the photodiodes also agree well with the simulated time dependence of the detected radiation.

Simulations of electrothermal instability growth in solid aluminum rods

“…Most of the attention thus far has been on the study of single mode 8 and multi-mode 9 magneto Rayleigh-Taylor (MRT) instability growth. 10 However, it is also important to understand the physics that precedes MRT instability growth including the physical processes of surface initiation [11][12][13] as current first begins to flow in a liner. In this context, the striation form of the electrothermal instability (referred to subsequently as just electrothermal instabilities) is particularly important since the wavevector of the instability allows for coupling to MRT instability growth.…”

Numerical simulation of metallic surface plasma formation by megagauss magnetic fields

“…Results from the Los Alamos National Laboratory (LANL) Lagrangian code Raven are also discussed. Results obtained by the Russian UP-MHD Lagrangian code are reported separately by Garanin, et al, in a companion paper in these proceedings [4].…”

“…As will be shown later, plasma forms near the initial surface and at very low density. This means that Lagrangian codes must expand by a large factor in a very small distance, necessitating very small initial computational cells [4]. Even with small initial cells, a yet-to-be-resolved issue is whether or not Lagrangian computations reach a sufficiently low density, since, in principle, the leading edge of an expansion material may have zero density.…”

“…Combination B is a combination that has been widely used to model wires and imploding liners, etc. Combination D is a SESAME-format implementation of analytic models developed at the All-Russian Scientific Research Institute of Experimental Physics (VNIIEF) and is approximately the same as the models described in [4]. As shown in the table, C combines a commonly used SESAME EOS with VNIIEF transport coefficients.…”

Study of the feasibility of warm dense matter generation using metal foil electric explosion under megaampere current drive

“…Simulations [9] suggest, however, that in addition to the comparatively hot (tens of electron volts) low-density coronal plasma generated on the surface of the metal, the interior of the aluminum post relaxes to a region of comparatively homogeneous dense plasma of about 4 eV temperature and ~60% initial solid density, i.e. the substance in the state of WDM [1].…”