Validating Copper Equation of State Models in Electrically Exploding Metal Rods with MHD Simulations

Abstract

The fundamental limits of high-current conduction and response of metal conductors to large, fast current pulses are of interest to high-speed fuses, exploding wires and foils, and magnetically driven dynamic material property and inertial confinement fusion experiments. A collaboration between the University of Nevada, Reno, University of New Mexico, and Sandia National Laboratory has fielded an electrically thick (R~400-μm > skin-depth) cylindrical metal rod target in a Z-pinch configuration driven by the Sandia 100-ns, 900-kA Mykonos linear transformer driver [1] . Photonic Doppler velocimetry (PDV) measuring the expansion velocity of pure copper rods [2] coated with ~30-μm of Parylene-N was used to benchmark magnetohydrodynamics simulations of the rods with the Los Alamos National Laboratory code FLAG [3] . Simulations of uncoated copper rods showed the metal surface followed the liquid-vapor coexistence curve to near the critical point. The dielectric coating, however, acts as an inertial tamper that opposes the rod’s expansion and compresses the surface into a low-density liquid as it heats up—eventually bypassing the vapor state and forming warm dense matter. The expansion velocities associated with simulations using various equation of state models were then compared to the PDV data to validate these models for MHD simulations of expanded Cu.