Verification and Validation of Magnetohydrodynamics Simulations of Electrically Exploded Conductors
Dense Z-pinches, magnetically-driven flyer plates, and electrically exploded wires and foils all take advantage of the extreme Lorentz forces and/or Ohmic heating generated by intense electrical current pulses through an initially solid conductor. Magnetohydrodynamics (MHD) simulations are used to interpret results of these pulsed power systems and design targets for future experiments. Formal testing of the numerical codes is necessary and broken into two categories: verification and validation. Verification tests how precisely a code solves the physics model implemented in it while validation describes how accurate the physics model is at capturing the system being modeled.MHD simulations of electrically exploded aluminum and copper rods demonstrate a novel technique to validate equations of state (EOS) for rapidly Ohmic-heated conductors. The single-fluid, resistive MHD code FLAG was used to simulate the phase transitions and bulk hydrodynamic motion of these conductors. The balance of internal and magnetic forces at the conductor-insulator interface drives the metal along the vaporization phase boundary. Variations between critical points and vaporization curves in existing models predict differing densities/temperatures in MHD simulations for these models. The inclusion of Maxwell constructs in the liquid/vapor biphase region of the EOS caused the rod surface to vaporize earlier in time than unmodified tables with Van der Waals (VdW) loops. Fully resolved 1D calculations did not heat up enough for the surface to exit the liquid/vapor biphase--suggesting 2D/3D effects are significant for plasma formation. Experimental velocimetry measurements were used to validate the location of the vaporization curve in existing EOS models and differentiate between the vapor dome treatments. Dielectric coatings applied to the metal surface restricted the conductor's expansion and diverted the metal into the warm dense matter regime.
Electrothermal Instability, High Energy Density, Magnetohydrodynamics, Mykonos, Photonic Doppler Velocimetry, Validation
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