P.We_79

1. LERMA Optically thick T hn Strong Absorption Precursor • Objectives • Defining and testing : • a compact electrical driver (1 kJ) • capable to launch quasi 1-D shocks in low pressure gases • suitable to test diagnostics before laser experiments • providing a benchmark for codes • easy to handle for training First tasks • Simulate shocks in a low pressure device • optimize the geometry • build a device • make tests Laser pulsed power Flux 1014 W.cm-2 Characteristic time <ns Energy > 50J Tube length ~ mm Tube diam 400µm to 1 mm Pressure 0.1 – 0.3 bar Shock speed > 60km/s Flux 109 W.cm-2 Characteristic time ~ µs Energy ~ kJ Tube length ~ cm Tube diam  1 mm Pressure ~ mbar Shock speed 5-30km/s Electron temperature Numerical simulation of 1D shocks • Hydro-rad MULTI code • Lagrangian description of the shock • Macroscopic approach of the plasma : • Density • Electron temperature • Mean charge Shock front Rad. precursor Te prec = T0 Te prec = T0 to 3T0 Te prec = T0 to 3T0 No precursor emerging precursor immediate precursor Exp (Kondo 2006) Rad. Limit Vrad MULTI simulation Shock speed km/s Mach number P.We_79 Strong shocks (M>>1), in gases achieved high T : Tshock ~ matom vshock2 Radiative absorption => heating / ionization shocked v T RADIATIVE SHOCKS hn hn MODIFICATION OF THE STRUCTURE OF THE SHOCK i.e. radiative precursor unshocked THEY RADIATE ! Shock : Highly supersonic : M >>1 Temperature Tshock~ 3 m u2/(16 k) ~ several 106K The accretion shocks are not resolved :radiative signatures (for instance in X rays) & models => accretion rate Principle of Radiative Shock generation with a laser ASTROPYSICAL CONTEXT YOUNG STARS Experimental study of strong shocks driven by compact pulsed powerJ. Larour1, J. Matarranz1, C. Stehlé2, N. Champion2, A. Ciardi21 Laboratoire de Physique de Plasmas LPP, UMR 7648, École Polytechnique, UPMC, CNRS, 91228 Palaiseau, France2 LERMA, UMR 8112, Observatoire de Paris, UPMC, CNRS, 5 Place J. Janssen, 92195 Meudon, France PALS iodine Laser in Prague (1 kJ, 1.3 mm, 0.3 ns) The laser is focalized on a foil, which converts the laser energy into mechanical energy. Young Star with his disk and accretion columns. Artist view taken from Brickhouse et al ApJ 2010 Where is the shock forming? Photosphere or chromosphere ?  different regimes for the radiation transport (optically thin or not ) accretion from the circumstellar disk to the photosphere;High velocity (free fall) : u ~  (2 GM/R)0.5400 km/s STANDARD CONDITION 60 km/s Xe P≤ 0.3 bar

2. First results with a conical tube Light (V) <Z> in shock 80 Pa air 11 caps 0.6µF 14kV Speed 6,7 km/s (Kondo: v=15km/s 80Pa Xe Mean charge Density Time (ns) Experimental scheme Principle of a Mather plasma focus (PF) few Torrs gas caps pinch insulator electrodes A plasma sheath, initiated by a surface flashover, is lanched by the jxB magnetic pressure Pumping & pressure regulation Ar Xe for shock tube HV power supply 15kV shock tube Current probe Conical electrodes Air for the switch Voltage measurement Optical fiber 11 caps 0.6µF switch Optimisation of conical electrodes Trigger 70 kV Marx generator Influence of tube shape Conical tube Straight tube Conclusion • Shocks of interest for astrophysics can be launched electrically • Gas pressure and electrode shaping can be optimized for getting high Mach number shocks and noticeable plasma temperature and gas ionisation. • A radial optical observation of the shock front with high spatial resolution and spectral capabilities is possible with a set of optical fibers. • Additional diagnostics are under implementation. Mass Speed Current Charge Position Shock tube by Kondo (IFSA 2005-2007) shorter tube by X 0.5 Kondo’s tube is Optimized for 200 Pa Xe A longer cone might be better at low P Straight tube vs conical tube : No change on current (amplitude, risetime) Mass of the plasma sheath smaller because the tube cross section decreases) Speed roughly x 2 longer tube by X 2 With and x~ 1 the snowplow factor Summary of simulation results Radiative regime at low pressure and high speed (P<100Pa, V> 10km/s Extended precursor in a low density gas >10cm Precursor temperature not sufficient for pre-ionising At 12.5 Pa Tmax ~ 9eV and <Z> ~ 8 P.We_79

3. LERMA Optically thick T First results with a conical tube hn Strong Absorption Light (V) Precursor 80 Pa air 11 caps 0.6µF 14kV Speed 6,7 km/s (Kondo: v=15km/s 80Pa Xe Time (ns) Laser pulsed power Flux 1014 W.cm-2 Characteristic time <ns Energy > 50J Tube length ~ mm Tube diam 400µm to 1 mm Pressure 0.1 – 0.3 bar Shock speed > 60km/s Flux 109 W.cm-2 Characteristic time ~ µs Energy ~ kJ Tube length ~ cm Tube diam  1 mm Pressure ~ mbar Shock speed 5-30km/s Experimental scheme Principle of a Mather plasma focus (PF) Summary of simulation results Hydro-rad MULTI, Lagrangian description of the shock Radiative regime at low pressure and high speed (P<100Pa, V> 10km/s Extended precursor in a low density gas >10cm Precursor temperature not sufficient for pre-ionising At 12.5 Pa Tmax ~ 9eV and <Z> ~ 8 few Torrs gas caps pinch insulator electrodes A plasma sheath, initiated by a surface flashover, is lanched by the jxB magnetic pressure Conclusion • Shocks of interest for astrophysics can be launched electrically • Gas pressure and electrode shaping can be optimized for getting high Mach number shocks and noticeable plasma temperature and gas ionisation. • A radial optical observation of the shock front with high spatial resolution and spectral capabilities is possible with a set of optical fibers. • Additional diagnostics are under implementation. P.We_79 shocked Radiative absorption => heating / ionization v T Strong shocks (M>>1), in gases achieved high temperatures : Tshock ~ matom vshock2 RADIATIVE SHOCKS hn hn MODIFICATION OF THE STRUCTURE OF THE SHOCK, i.e. radiative precursor unshocked THEY RADIATE ! Principle of Radiative Shock generation with a laser ASTROPYSICAL CONTEXT YOUNG STARS Shock : Highly supersonic : M >>1 Temperature Tshock~ 3 m u2/(16 k) ~ several 106K The accretion shocks are not resolved :radiative signatures (for instance in X rays) & models => accretion rate PALS iodine Laser in Prague (1 kJ, 1.3 mm, 0.3 ns) Experimental study of strong shocks driven by compact pulsed powerJ. Larour1, J. Matarranz1, C. Stehlé2, N. Champion2, A. Ciardi21 Laboratoire de Physique de Plasmas LPP, UMR 7648, École Polytechnique, UPMC, CNRS, 91228 Palaiseau, France2 LERMA, UMR 8112, Observatoire de Paris, UPMC, CNRS, 5 Place J. Janssen, 92195 Meudon, France The laser is focalized on a foil, which converts the laser energy into mechanical energy. Young Star with his disk and accretion columns. Artist view taken from Brickhouse et al ApJ 2010 Where is the shock forming? Photosphere or chromosphere ?  different regimes for the radiation transport (optically thin or not ) STANDARD CONDITIONS : 60 km/s Xe P ≤ 0.3 bar accretion from the circumstellar disk to the photosphere;High velocity (free fall) : u ~  (2 GM/R)0.5400 km/s • Objectives • Defining and testing : • a compact electrical driver (1 kJ) • capable to launch quasi 1-D shocks in low pressure gases • suitable to test diagnostics before laser experiments • providing a benchmark for codes • easy to handle for training First tasks • Simulate shocks in a low pressure device • optimize the geometry • build a device • make tests