Viscosity measurements of shock-compressed Epoxy*

Viscosity gives insight into the momentum transport in a system and plays a crucial role in mixing and growth of hydrodynamic instabilities. Viscosity measurements in High Energy Density (HED) states are particularly important to accurately develop hydrodynamic models and to bridge the gap between simulations and experimental results of complex systems such as Inertial Confinement Fusion. We measured viscosity in dynamically compressed Stylist 1266 (CH, 1.1 g/cc) by tracing the acceleration of particles embedded in the target. The OMEGA-60 laser facility was used to drive a shock (?240 GPa) through the CH target, which was embedded with 40 and 60 μm stainless steel spherical particles (7.8 g/cc) that would be accelerated by the flow behind the shock. The particle positions were recorded with time-resolved X-ray radiography. The velocities of the particles and CH were used to determine the viscous and inviscid force contributions acting on the particles using a shock-particle forcing model. From the forces, we calculated the dynamic viscosity of CH to be less than 10 Pa-sec . A Bayesian inference analysis on the force model was performed to determine the probability distribution of viscosity for a given range of input variables.