A Novel Technique to Measure the Viscosity of Solid MgO at High Pressures and Strain Rates Using Laser-Driven Richtmyer-Meshkov Instabilities

Solids are often assumed to behave as viscous fluids under high-strain rates. This behavior has been studied experimentally in metals but rarely with a brittle ceramic material. In this study, we present a new technique for measuring the viscosity of MgO using time-resolved velocimetry to track the growth rate of Richtmyer-Meshkov instabilities generated by laser shock compression at the OMEGA EP laser facility. To interpret the results, we use an in-house Eulerian hydrocode to simulate our experiments and model the plastic deformation of solid MgO as a highly viscous fluid. Results indicate that MgO has a surprisingly low upper bound to its effective viscosity of ~100 Pa*s at 175(15) GPa, ~3500 K, and ~10^6 s^-1 strain rate.