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).We measured the dynamic viscosity of epoxy at high pressures (peak⁓248 GPa) by tracing the motion of stainless steel particles embedded in the target. The OMEGA-60 laser facility was utilized to generate shocks within a Stycast 1266 (epoxy, 1.1 g/cc) target, causing the displacement and deformation of spherical particles under the forces applied by the surrounding epoxy. Time-resolved X-ray radiography recorded the particle positions, 2D xRAGE simulations of the experiments were also used to calculate the fluid velocity and density.These measurements were used in determining the viscous and inviscid force contributions using a shock-particle forcing model. The forces thus obtained are used to calculate dynamic viscosity. Additionally, a Bayesian inference analysis of the force model was employed to reconstruct the particle displacement for given viscosity at a given range of input parameters. The integration of experimental data and simulation results yields valuable insights into the behavior of Epoxy under extreme conditions, offering essential data for various high-pressure applications.