Numerical simulation of metallic surface plasma formation by megagauss magnetic fields

Plasma formation on the surface of thick metal in response to a pulsed multi-megagauss magnetic field is being investigated at the University of Nevada, Reno, using aluminum rods that have radii larger than the magnetic skin depth. US and Russian radiation-magnetohydrodynamic codes are being used to help interpret the experimental results such as time of plasma formation and rate of current channel expansion. The best results obtained to date with the UNR code MHRDR use a standard SESAME Maxwell-construct EOS and a Russian resistivity model, and the computed times of formation agree well with the observations across the full range of wire diameters. This leads to the conclusion that plasma formation is an MHD effect and does not involve the non-MHD processes often evoked in other contexts. The computations show that plasma is formed in low-density material that is resistive enough to expand across the magnetic field and yet conductive enough that Ohmic heating exceeds expansion cooling as the expanding material undergoes the liquid-vapor transition.