Viscosity Measurements in 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 (ICF). Inclusion of viscous dissipation in the modelling of ICF implosions has led to a better understanding of hot spot turbulence (C. R. Weber, 2014), (B. M. Haines, 2014), demonstrating the importance of further studies in the direction.

We measured viscosity at high pressures (peak⁓248 GPa), in CH under laser-driven shock compression.We measured viscosity in dynamically compressed Stycast 1266 (CH, 1.1

g/cc) by tracing the acceleration of particles embedded in the target. The OMEGA-60 laser facilitywas used to drive a shock (peak⁓248 GPa) through the CH target, which was embedded with stainless steel (7.8 g/cc) and titanium (4.56 g/cc) microspheres that were accelerated by the flow behind theshock. The particle positions were recorded with time-resolved X-ray radiography. The velocities of the particles and Stycast 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 Epoxy to be O(1) Pa-sec. We have perfomed X-ray diffraction experiments to determine the physical state of shocked Epoxy, to understand its effect on the magnitude of viscosity. A Quasi-steady analysis of the problem is also being performed to study the viscous effects on deformed particle and compare it with the viscosity calculated from the force model.