The influence of preformed plasma on a laser-driven shock produced in a planar target at the conditions relevant to shock ignition

The effect of preformed plasma on a laser-driven shock produced in a planar target at the conditions relevant to the shock ignition scenario of ICF was investigated at the kilojoule PALS laser facility. Characteristics of the preformed plasma were controlled by the delay Δt between the auxiliary beam (1ω, 7×1013 W/cm2) and the main 3ω, 250 ps laser pulse of intensity up to 1016 W/cm2, and measured with the use of 3-frame interferometry, ion diagnostics, an X-ray spectrometer and Kα imaging. Parameters of the shock produced in a CH(Cl) target (25 μm or 40 μm thick) by the intense 3ω laser pulse with energy ranging between 50 J and 200 J were determined by measuring the craters produced by the shock in a massive Cu target behind the layer of plastic. The volume and the shape of these craters was found to depend rather weakly on the preplasma thickness, which implies the same is true for the total energy of shocks and pressure generated by them. From the comparison of the measured crater parameters with those obtained in 2D simulations using the PALE code, it was estimated that for I3ω 1016 W/cm2 the pressure at the rear (non-irradiated) side of the 25-μm plastic layer reaches about 100 Mbar. Copyright © (2013) by the European Physical Society (EPS)