Design and Optimization of MAPS Experiments on Sandia's Z Machine

Summary form only given. Magnetically-applied pressure-shear (MAPS) is a recently developed technique to directly measure material shear strength using magnetohydrodynamic (MHD) pulsed power platforms1,2. The method has been prototyped on Sandia's Veloce pulser, but was limited to strength measurements at modest pressures of ~10 GPa. Our present aim is to develop MAPS into a robust technique to measure strength at higher pressure achievable on Sandia's Z pulsed power machine.By applying an external static magnetic field to a tri-layer driver/sample/anvil region, the MHD drive directly induces a shear stress wave in addition to the usual longitudinal stress wave. The longitudinal and shear deviatoric stresses are coupled through a von Mises yield criterion, hence the transmissible shear wave at a given pressure is limited by the sample material strength. The transmitted pressure and shear are directly related to the measured free surface velocities of the anvil which are measured using a transverse VISAR diagnostic. Complex wave interactions among forward and reflected longitudinal and shear waves, the advancing magnetic diffusion front of the MHD drive, the shape of the current drive, as well as the applied magnetic field strength and uniformity, can make the design of the experiments complex. This paper will present the design and optimization of MAPS experiments to be fielded on Z. The MAPS experiments are modeled using Sandia's ALEGRA MHD code. We will detail the numerical investigations into MHD shear generation, longitudinal and shear wave coupling, timing of the wave interactions, and transmission of shear at material interfaces.