HYPERSONIC SHOCKS : THE ROLE OF RADIATION
Chantal Stehlé1, Michaela Kozlová2, Jean Larour3, Jaroslav Nejdl2, Norbert Champion1, Patrice Barroso4, Francisco Suzuki-Vidal5, Ouali Acef6, Pierre-Alexandre Delattre1, Jan Dostál2, Miroslav Krus2, Jean-Pierre Chièze7.
1 LERMA, UMR 8112, Observatoire de Paris, UPMC, CNRS, 5 Place J. Janssen, 92195 Meudon, France
2 Institute of Physics of ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic
3 Laboratoire de Physique des Plasmas, UMR 7648, Ecole Polytechnique, UPMC, CNRS, 91128 Palaiseau, France
4 GEPI, UMR 8111, Observatoire de Paris, Paris Diderot, CNRS, 5, place Jules Janssen, 92195 Meudon, France
5 The Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2AZ, UK
6 SYRTE, UMR8630, Observatoire de Paris, UMPC, CNRS, 61, Av. de l´Observatoire, 75014 Paris, France
7 IRFU/Service d´Astrophysique, CEA-Saclay, 91191 Gif sur Yvette, France
Abstract. Producing experimental radiative shocks is known to be feasible using high-energy laser installations. Radiative shocks are characterized by an ionization front induced by the shock wave. For a given shock velocity, which is set by the available laser energy, and a given initial gas pressure, the radiative effects are more important for a high atomic number. It is why xenon is commonly used for such objective.
A laser fluence of 1014 W/cm2 onto a thin foil is sufficient to drive a shock wave at an initial velocity of about 60 km/s. The shock propagates in a square or cylindrical shock tube of typical dimensions of 700 x 700 microns2 or less, depending on the available energy, and of length of few mm allowing to study the propagation over times up to 50 ns. It is first expected that the dynamics of the shock does not change with the shock section. However, it is proved that the lateral radiation losses through the cell windows strongly impact the shock dynamics.
Thus, the role played together by opacity and geometry is critical for the physics of radiative shock waves. Moreover, radiation is an obvious way of probing the shock waves, either by self emission or by probe absorption. These aspects will be illustrated by recent experimental results obtained at the iodine PALS laser facility in Prague.
The research leading to these results has received funding from the European Community's Seventh Framework Programme under grant agreement n° 228334 (LASERLAB-Europe II), and from the French ANR STARSHOCK (contract ANR-08-BLAN-0263-07).