Experimental study of strong shocks driven by compact pulsed power J. Larour 1, J. Matarranz 1, C. Stehlé 2, N. Champion 2, A. Ciardi 2 1 Laboratoire de Physique de Plasmas LPP, UMR 7648, École Polytechnique, UPMC, CNRS, Palaiseau, France 2 LERMA, UMR 8112, Observatoire de Paris, UPMC, CNRS, 5 Place J. Janssen, Meudon, France P.We_79 LERMA Strong shocks (M>>1), in gases achieved high T : T shock ~ m atom v shock 2 T v unshocked shocked Radiative absorption => heating / ionization h h Precursor Optically thick h Strong Absorption T THEY RADIATE ! MODIFICATION OF THE STRUCTURE OF THE SHOCK i.e. radiative precursor RADIATIVE SHOCKS ASTROPYSICAL CONTEXT YOUNG STARS accretion from the circumstellar disk to the photosphere; High velocity (free fall) : u ~ (2 GM/R) 0.5  400 km/s Shock : Highly supersonic : M >>1 Temperature T shock ~ 3 m u 2 /(16 k) ~ several 10 6 K The accretion shocks are not resolved : radiative signatures (for instance in X rays) & models => accretion rate 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 ) The laser is focalized on a foil, which converts the laser energy into mechanical energy. PALS iodine Laser in Prague (1 kJ, 1.3  m, 0.3 ns) STANDARD CONDITION 60 km/s Xe P  ≤ 0.3 bar Principle of Radiative Shock generation with a laser 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 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 10 9 W.cm -2 Characteristic time ~ µs Energy ~ kJ Tube length ~ cm Tube diam  1 mm Pressure ~ mbar Shock speed 5-30km/s T e prec = T 0 T e prec = T 0 to 3T 0 T e prec = T 0 to 3T 0 No precursor emerging precursor immediate precursor 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 speed km/s Mach number Exp (Kondo 2006) Rad. Limit Vrad MULTI simulation Shock front Rad. precursor

P.We_79 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. in shock Mean charge Density HV power supply 15kV Current probe Conical electrodes Trigger shock tube Pumping & pressure regulation Optical fiber 11 caps 0.6µF 70 kV Marx generator switch Voltage measurement Air for the switch Ar Xe for shock tube 80 Pa air 11 caps 0.6µF 14kV Speed 6,7 km/s (Kondo: v=15km/s 80Pa Xe First results with a conical tube Light (V) Time (ns) Shock tube by Kondo (IFSA ) shorter tube by X 0.5 longer tube by X 2 Kondo’s tube is Optimized for 200 Pa Xe A longer cone might be better at low P Optimisation of conical electrodes Summary of simulation results Radiative regime at low pressure and high speed (P 10km/s Extended precursor in a low density gas >10cm Precursor temperature not sufficient for pre-ionising At 12.5 Pa Tmax ~ 9eV and ~ 8 Experimental scheme Principle of a Mather plasma focus (PF) A plasma sheath, initiated by a surface flashover, is lanched by the jxB magnetic pressure caps few Torrs gas pinch insulatorelectrodes With and  ~ 1 the snowplow factor Straight tube Conical tube Mass Speed Current Charge Position 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 Influence of tube shape

Experimental study of strong shocks driven by compact pulsed power J. Larour 1, J. Matarranz 1, C. Stehlé 2, N. Champion 2, A. Ciardi 2 1 Laboratoire de Physique de Plasmas LPP, UMR 7648, École Polytechnique, UPMC, CNRS, Palaiseau, France 2 LERMA, UMR 8112, Observatoire de Paris, UPMC, CNRS, 5 Place J. Janssen, Meudon, France P.We_79 LERMA Strong shocks (M>>1), in gases achieved high temperatures : T shock ~ m atom v shock 2 T v unshocked shocked Radiative absorption => heating / ionization h h Precursor Optically thick h Strong Absorption T THEY RADIATE ! MODIFICATION OF THE STRUCTURE OF THE SHOCK, i.e. radiative precursor RADIATIVE SHOCKS ASTROPYSICAL CONTEXT YOUNG STARS accretion from the circumstellar disk to the photosphere; High velocity (free fall) : u ~ (2 GM/R) 0.5  400 km/s Shock : Highly supersonic : M >>1 Temperature T shock ~ 3 m u 2 /(16 k) ~ several 10 6 K The accretion shocks are not resolved : radiative signatures (for instance in X rays) & models => accretion rate 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 ) The laser is focalized on a foil, which converts the laser energy into mechanical energy. PALS iodine Laser in Prague (1 kJ, 1.3  m, 0.3 ns) STANDARD CONDITIONS : 60 km/s Xe P  ≤ 0.3 bar Principle of Radiative Shock generation with a laser 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. 80 Pa air 11 caps 0.6µF 14kV Speed 6,7 km/s (Kondo: v=15km/s 80Pa Xe First results with a conical tube Light (V) Time (ns) Summary of simulation results Hydro-rad MULTI, Lagrangian description of the shock Radiative regime at low pressure and high speed (P 10km/s Extended precursor in a low density gas >10cm Precursor temperature not sufficient for pre- ionising At 12.5 Pa Tmax ~ 9eV and ~ 8 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 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 10 9 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) A plasma sheath, initiated by a surface flashover, is lanched by the jxB magnetic pressure caps few Torrs gas pinch insulatorelectrodes