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We report on the design and first results from experiments looking at the formation of radiative shocks on the Shenguang-II (SG-II) laser at the Shanghai Institute of Optics and Fine Mechanics in China. Laser-heating of a two-layer CH/CH–Br foil drives a $\sim 40$ km/s shock inside a gas cell filled with argon at an initial pressure of 1 bar. The use of gas-cell targets with large (several millimetres) lateral and axial extent allows the shock to propagate freely without any wall interactions, and permits a large field of view to image single and colliding counter-propagating shocks with time-resolved, point-projection X-ray backlighting ($\sim 20$ μm source size, 4.3 keV photon energy). Single shocks were imaged up to 100 ns after the onset of the laser drive, allowing to probe the growth of spatial nonuniformities in the shock apex. These results are compared with experiments looking at counter-propagating shocks, showing a symmetric drive that leads to a collision and stagnation from $\sim 40$ ns onward. We present a preliminary comparison with numerical simulations with the radiation hydrodynamics code ARWEN, which provides expected plasma parameters for the design of future experiments in this facility.
We report on the investigation of strong radiative shocks generated with the high energy, sub-nanosecond iodine laser at PALS. These shock waves are characterized by a developed radiative precursor and their dynamics is analyzed over long time scales (~50 ns), approaching a quasi-stationary limit. We present the first preliminary results on the rear side XUV spectroscopy. These studies are relevant to the understanding of the spectroscopic signatures of accretion shocks in Classical T Tauri Stars.
In our commission the vice-president (VP) becomes the president, and a new VP is chosen from members of the Organizing Committee. The position of secretary was discontinued and its responsibilities incorporated into the VP position. The president announced that the new officers are Steven R. Federman (president) and Glenn M. Wahlgren (vice-president).
Radiative shock waves are observed around astronomical objects in a
wide variety of environments, for example, they herald the birth of stars
and sometimes their death. Such shocks can also be created in the
laboratory, for example, by using energetic lasers. In the astronomical
case, each observation is unique and almost fixed in time, while shocks
produced in the laboratory and by numerical simulations can be reproduced,
and investigated in greater detail. The combined study of experimental and
computational results, as presented here, becomes a unique and powerful
probe to understanding radiative shock physics. Here we show the first
experiment on radiative shock performed at the PALS laser facility. The
shock is driven by a piston made from plastic and gold in a cell filled
with xenon at 0.2 bar. During the first 40 ns of the experiment, we have
traced the radiative precursor velocity, that is showing a strong decrease
at that stage. Three-dimensional (3D) numerical simulations, including
state-of-art opacities, seem to indicate that the slowing down of the
precursor is consistent with a radiative loss, induced by a transmission
coefficient of about 60% at the walls of the cell. We infer that such 3D
radiative effects are governed by the lateral extension of the shock wave,
by the value of the opacity, and by the reflection on the walls. Further
investigations will be required to quantify the relative importance of
each component on the shock properties.