Numerical simulations for the design of absolute equation-of-state measurements by laser-driven shock waves

Summary. — A recently proposed experiment for the absolute measurement of the Equation of State (EOS) of solid materials in the 10‐50 Mbar pressure range is analyzed by means of numerical simulations. In the experiment, an intense laser pulse drives a shock wave in a solid target. The shock velocity and the fluid velocity are measured simultaneously by rear side time-resolved imaging and by transverse X-radiography, respectively. An EOS point is then computed by using the Hugoniot equations. The target evolution is simulated by a two-dimensional radiationhydrodynamics code; ad hoc developed post-processors then generate simulated diagnostic images. The simulations evidence important two-dimensional effects, related to the finite size of the laser spot and to lateral plasma expansion. The first one may hinder detection of the fluid motion, the second results in a decrease of the shock velocity with time (for constant intensity laser pulses). A target design is proposed which allows for the accurate measurement of the fluid velocity; the variation of the shock velocity can be limited by the choice of a suitably time-shaped laser pulse.