P (TW)

1. Parametric instabilities Ps DT Référence =1,9.1014 W/cm² TR TF Ps/2 5 mg = 290 km/s Mass=0,59mg 1 mg = 650g/cc Hydrodynamic instabilities t =1,2 0,5 mg Simple, spherical and scalable target 1044µm 522µm 814µm 1250µm 1570µm Return shock 0,1 mg CHIC simulations Rosen model ICF Context HIPER target shock ignition robustness 0,01 mg h = 0,5 Inertial Confinement Fusion h = 1 h = 2 Classical schemes Alternative schemes Direct-Drive Fusion Indirect-Drive Fusion Fast Ignition Shock Ignition Hole boring, impact ignition 250ps Absorbed spike power Shock launching time Central hot spot ignition Ignition by relativistic electron beams Ignition by a strong convergent shock Compression :180 kJ into 10 ns (50TW) + ETN=20 MJ Gain = 80 Ignition : 80 kJ into 500 ps (150TW) P (TW) Ignition pulse HIPER target Compression pulse Standart impulsion duration t (ns) The laser typerequired is the same for both compression and ignition stages Laser • Compression and ignition stages are partially uncoupled • Low isentrope fuel assembly • Classical medium implosion velocity (≈ 290km/s) in opposition to conventional hot spot ignition (≈350-400km/s) Betti.R et al. Phys. Rev. Letters, 98, 155001 (2007) Homothetic targets performance study Shock ignition principle Phs ρsh Hot Spot Psh ρhs Shell Fuel non-isobaric parameter rHS rSH Hot spot ignition condition : The self-heating condition for non-isobaric case can be written as : When : isobaric configuration The hot spot enters the ignition domain with specific values of and which depends on the fuel non isobaric parameter ε Shock ignition performance domain Gain model The Rosen and Lindl model has been reviewed taking into consideration the influence of the non-isobaric nature of the fuel induced by the ignitor shock: M.D.Rosen and J.D.Lindl (1984) UCRL-50021-83 PL=110TW Intensity (1015 W/cm²) PL=130TW Fuel mass shell adiabat at stagnation defining the hot spot at ignition instant: coupling efficiency between the laser energy and the internal DT fuel energy PL=340TW shell pressure At constant mass, Rosen model shows the low threshold and high gain possibility of a non-isobaric configuration. CHIC simulations are well-described by the Rosen model Pressure amplification Conclusions and prospects Guderley self-similar solution in spherical symmetry for an ideal gas ( ) : 300 Gbars Optimal shocks collision : Ignitor shock Amplification by a factor 6 The shock ignition pressure amplification and the spherical effect are well-described by the Guderley model 0,7 Gbars Convergent shock Guderley solution CHIC shock pressure Von Guderley.G, Luftfahrt-Forsch, 9, 302, (1942) Shock ignition : modelling elements and target robustness M. Lafon, X. Ribeyre and G. Schurtz Centre Lasers Intenses et Applications, Université Bordeaux 1- CNRS - CEA Iso-thermonuclear energy curves Run series of CHIC 1D using radial rays and total energy absorption at critical Ribeyre, X et al., Plasma Phys. Cont. Fusion, 51, 015013 (2009) How does it work ? Ignition pulse robustness Spike power time shape Laser time rise : TR =TF = 200 ps If spike duration decreases about 50%, thermonuclear energy only decreases about 15% Pulse duration at FWHM : TM+ΔT+TD The spike power remains constant : PS=cte The ignition mainly depends on the spike power and not on the spike energy • A strong convergent shock is produced by ignition pulse • The ignitor shock catches up the compression shock reflected at the center of the target near the inner interface of the shell • The resulting assembly shows that the hot spot pressure is greater than the surrounding fuel pressure that leads to ignition Non-isobaric configuration For all targets : In the shock ignition scheme, the high nonisobaric nature of the final fuel leads to achieve the ignition conditions The intensity threshold required for ignition is not homothetic : Pshock is not varying by h² The required spike power strongly increases when the implosion velocity decreases (< 240 km/s) Beyond 350 km/s, the HIPER target self-ignites There is to reach a compromise between the target intensity and the implosion velocity In the shock ignition scheme, the implosion velocity field is optimal for the range 240 < Vimp (km/s) < 290 • Runs of simulations 1D shows the robustness of the shock ignition scheme • The spike impulsion leading to ignition mainly depends on spike power and not on spike energy • The Rosen model study shows the influence of the non-isobaric parameter : at constant mass, the laser energy required for ignition is lower for the shock ignition scheme than for the classical isobaric configuration scheme • The shock ignition pressure evolution is well-described by the Guderley model during convergence • The required spike laser power family is not homothetic with the target size for a family of homothetic targets: the power threshold does not increase as much as the homothetic factor of the target size • An optimal domain of use might be defined by making a compromise between the intensity on target and the implosion velocity • A study on 2D effetcs will be performed • The analytical model has to be detailed and improved using the Guderley model in order to best describe the shock dynamics • Hydrodynamic instabilities have to be evaluated according to the target irradiation symmetry • The limiting factors of laser-plasma interaction must be defined, especially concerning the parametric instabilities