NUMERICAL SIMULATIONS FOR THE DESIGN OF ABSOLUTE EQUATION-OF-STATE MEASUREMENTS BY LASER-DRIVEN SHOCK-WAVES

A recently proposed experiment for the absolute measurement of the Equ ation of State (EOS) of solid materials in the 10-50 Mbar pressure ran ge is analyzed by means of numerical simulations. In the experiment, a n intense laser pulse drives a shock wave in a solid target. The shock velocity and the fluid velocity are measured simultaneously by rear s ide time-resolved imaging and by transverse X-radiography, respectivel y. An EOS point is then computed by using the Hugoniot equations. The target evolution is simulated by a two-dimensional radiation-hydrodyna mics code; ad hoc developed post-processors then generate simulated di agnostic images. The simulations evidence important two-dimensional ef fects, related to the finite size of the laser spot and to lateral pla sma 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 a llows for the accurate measurement of the fluid velocity; the variatio n of the shock velocity can be limited by the choice of a suitably tim e-shaped laser pulse.