New insights on the physics of radiative shocks

International audienceShock waves play a significant role in several astrophysical phenomena. Among them, Radiative shocks are strong shocks, in which the shock front is heated to very high temperature and thus emit an important radiation flux. The interesting feature of the radiative shocks is that their structure is strongly influenced by the coupling between hydrodynamics and radiation. They occur in astrophysical system in the different stages of the stellar evolution, for instance during the accretion processes in the stellar infancy, and are studied in high-energy density laboratory experiments using kJ class lasers. Such laser facilities enable to drive shocks in which the radiative flux may prevail hydrodynamic mechanism of energy transfer. Typical irradiances of 10**14 W.cm-2, allows to produce radiative shocks in high atomic gas medium at low pressure, where the important radiation generated by the shocked plasma leads to the formation of an ionizing wave, also call radiative precursor, in the cold upstream xenon. I will present new experimental results realized on the PALS laser installation aiming at improving the present knowledge of these complex flows. The greatest attention is paid to the application of to new diagnostics, namely, the instantaneous imaging of the whole shock structure using an auxiliary laser at 21.2 nm and a time-and-space resolved plasma self-emission using fast diodes. This work is supported by french ANR STARSHOCK (grant 08-BLAN-0263-07) and by Laserlab-Europe II programme

New probing techniques of radiative shocks

International audienceRadiative shock waves propagating in xenon at a low pressure have been produced using 60 joules of iodine laser (λ = 1.315 μm) at PALS center. The shocks have been probed by XUV imaging using a Zn X-raylaser (λ = 21 nm) generated with a 20-ns delay after the shock creating pulse. Auxiliary high-speed silicon diodes allowed performing space- and time-resolved measurement of plasma self-emission in the visible and XUV. The results show the generation of a shock wave propagating at 60 km/s preceded by a radiative precursor. This demonstrates the feasibility of radiative shock generation using high power infrared lasers and the use of XRL backlighting as a suitable diagnostic for shock imaging

New diagnostics of laser generated shocks

International audienceStrongly radiative shocks are characterized by an ionization front induced by the shock wave. The role played together by opacity and geometry is critical for the physics of these shock waves. Moreover, radiation is an obvious way of probing these shock waves, either by self-emission or by probe absorption. These aspects will be illustrated by recent experimental results obtained at the iodine PALS (Prague Asterix Laser System) facility

New diagnostics of laser generated shocks

International audienceStrongly radiative shocks are characterized by an ionization front induced by the shock wave. The role played together by opacity and geometry is critical for the physics of these shock waves. Moreover, radiation is an obvious way of probing these shock waves, either by self-emission or by probe absorption. These aspects will be illustrated by recent experimental results obtained at the iodine PALS (Prague Asterix Laser System) facility