Viscosity Measurements in CH at extreme conditions

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 epoxy (CH, 1.1 g/cc) by tracing the acceleration of particles embedded in the target. The OMEGA-60 laser facility was used to generate laser beams to drive a shock (peak⁓248 GPa) through the CH target, which was embedded with stainless steel (7.8 g/cc) or tungsten (19.3 g/cc) microspheres that were accelerated by the flow behind the shock. The particle positions were recorded with time-resolved X-ray radiography. The velocity of CH was calculated with the VISAR shock speed and the relation for polystyrene [1]. 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 viscous unsteady force, we determined the dynamic viscosity of shock compressed CH to be less than 10 Pa.sec.

References

[1] M.A. Barrios, D.G. Hicks, T.R. Boehly, D.E. Fratanduono, J.H. Eggert, P.M. Celliers, G.W. Collins, and D.D. Meyerhofer. “High-precision measurements of the equation of state of hydrocarbons at 1-10 Mbar using laser-driven shock waves,” Physics of Plasmas, 17, 056307 (2010).