Magnetic diffusion in conductors at ultrahigh current density

Summary form only given. Recent experiments on the Z-Accelerator at Sandia National Laboratories were performed to characterize magnetic diffusion in aluminum and copper at currents of 3-4MA/cm and pulsewidths of 200ns. Principal diagnostics include a unique type of B-dot probe and VISAR laser interferometry. Streak camera spectroscopy and pyrometry were also fielded on representative shots. These experiments were designed to allow comparison between magnetic field diffusion rate and the pressure wave propagation resulting in the onset of motion. As the magnetic field diffuses into the conductive material the current causes joule heating which changes both the thermal and electrical conductivity of the material resulting in energy losses. These nonlinear effects are not well known at these current densities Magnetic diffusion and energy deposition are important in several areas including the following. First, it is desirable to understand the losses associated with magnetic diffusion for the upward power scaling of the next generation Z-Accelerator, and to characterize potential construction materials. Second, it is necessary to understand the rate of magnetic diffusion when designing isentropic compression experiments on solids such that materials and sample thickness can be selected in order to study pressure wave loading and unloading without the confounding effects of magnetic diffusion. Third, there is an ongoing push to improve the predictive capabilities of magnetohydrodynamic (MHD) codes such as MACH2 and Alegra in order to more accurately model experiments in this current density regime. Fourth, several groups are interested in understanding the physics of exploding wires driven by very high currents. And finally, several other groups are interested in magnetized target fusion, which incorporates driven aluminum liners used to compress a plasma in a field reversed configuration.