Self-consistent, two-dimensional, magnetohydrodynamic simulations of magnetically driven flyer plates

Abstract

The intense magnetic field generated by the 20 megaampere Z machine [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] at Sandia National Laboratories is being used as a pressure source for material science studies. An application we have studied in great detail involves using the intense magnetic field to accelerate flyer plates (small metal disks) to very high velocities (>20 km/s) for use in shock loading experiments. We have used two-dimensional (2D) magnetohydrodynamic (MHD) simulation to investigate the physics of accelerating flyer plates using multi-megabar magnetic drive pressures. A typical shock physics load is comprised of conducting electrodes that are highly compressible at multi-megabar pressures. Electrode deformation that occurs during the rise time of the current pulse causes significant inductance increase, which reduces the peak current (drive pressure) relative to a static geometry. This important dynamic effect is modeled self-consistently by driving the MHD simulation with an accurate circuit model of Z. Self-consistent, 2D, MHD simulations are able to produce and predict time resolved velocity interferometry measurements when the drive circuit includes models of current losses and short circuiting in Z. Simulation results elucidate the phenomena contributing to the flyer velocity history, and show that electrical and hydrodynamic optimization of the load are necessary to minimize effects of time varying inductance. Details of the modeling, the physics, and comparisons with experiment are presented.