Experimental study of counter propagating radiative shocks

International audienceS 04 Atelier général PNPS Radiative shocks are present at different stages of stellar evolution, for instance in the stellar infancy when matter is accreted from the stellar disk to the photosphere of the young star and is also ejected in the form of stellar jets, up to the final stages as supernovae and the interaction of their remnants with the interstellar medium. Such shocks are strongly influenced by the radiation through its coupling with hydrodynamics. Thus their topology and dynamics are quite complex. Generating such hypersonic shocks in the laboratory, with controlled conditions, is thus an adequate tool to study the influence of radiation and to compare them with numerical simulations. So far, such laboratory astrophysics studies are performed on large-scale laser facilities, addressing hydrodynamic radiative shocks, in Xenon with very high velocity (50 - 150 km/s) and moderate pressure (0.1 - 1 bar). These experiments advance the understanding of the effect of radiation on the different shock components (radiative precursors, shock collapse, walls heating etc.). In continuation of these laboratory experiments, we recently performed experiments at PALS laser facility to study a fairly new topic focusing on the interaction of two counter propagating shocks. The objective is to understand the influence of one radiative precursor onto another, to achieve higher temperature in the compressed medium. In the astrophysical context, aforementioned studies are relevant for instance, collision of supernovae remnants and more indirectly the interaction of supernovae remnants with dense molecular clouds and the impact of accretion flows on a stellar atmosphere. The experiments have been able to launch shocks with different shock speeds (~30-55 km/s and 10-25 km/s), in varying gases (Ar, Xe) and pressures (~0.1-0.3 bar). Optical interferometry allowed us to estimate several physical parameters such as shock speed and electron density in the precursor, XUV spectroscopy allowed to give information about the shock temperature. We will present some preliminary results together with numerical simulations