Adiabatic Index in Shock‐Compressed Beryllium

We present a method to measure the adiabatic index of a material under shock compression by X-ray Thomson Scattering. A beryllium target is symmetrically compressed by two counterpropagating shock waves that collide in the target center, producing super dense states of matter of up to 6 fold compression. We measure the density before and after the shock collision and solve the Hugoniot relations for colliding shocks to infer the adiabatic index. Our results indicate that the adiabatic index stays rather high even in the high compression regime. This agrees with a linear scaling model taken from the SESAME equation of state and shows that the adiabatic index becomes significantly different from the ratio of heat capacities in this strongly coupled plasma (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)