Experimental observation of elevated heating in dynamically compressed CH foam

Abstract

We present an experimental result of significantly increased heating in a laser-driven blastwave experiment carried out at the OMEGA laser facility. Abnormally high temperatures were observed in warm dense CH compared to older experiments and theoretical predictions. The higher temperatures in compressed CH were linked to an improved smoothness of the laser intensity profile, which resulted in better efficiency of the drive and coupling of more energy into the system compared to previous similar experiments. Fifteen beams with combined intensity of ∼7 1014 W cm-2 and a square intensity profile with 2 ns duration were used to drive a strong shock, which subsequently developed to a blastwave travelling through low density CH foam creating warm dense matter. Multiple diagnostics were used to examine the thermodynamic conditions in the warm dense CH foam. Velocity interferometry (VISAR) and streaked pyrometry (SOP) observed increased blastwave velocities, while x-ray Thomson scattering (XRTS) measured elevated temperatures of 17.5 - 35 eV in compressed CH foam. The experimental results were compared to hydrodynamic simulations and a potential contribution from x-rays to the elevated temperatures in the dense material was considered.