1. P (TW) t (ns) ICF Context Inertial Confinement Fusion Classical schemes Direct-Drive Fusion Indirect-Drive Fusion Central hot spot ignition Alternative schemes Fast Ignition Shock Ignition Hole boring, impact ignition Ignition by relativistic electron beams Ignition by a strong convergent shock How does it work ? Homothetic targets performance study = 290 km/s =1,9.10 14 W/cm² = 650g/cc =1,2 The intensity threshold required for ignition is not homothetic : P shock is not varying by h² Shock ignition principle Non-isobaric configuration 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 In the shock ignition scheme, the high nonisobaric nature of the final fuel leads to achieve the ignition conditions Fuel non-isobaric parameter Convergent shock Ignitor shock Return shock Pressure amplification 0,7 Gbars 300 Gbars Optimal shocks collision : Amplification by a factor 6 CHIC shock pressure Guderley solution Guderley self-similar solution in spherical symmetry for an ideal gas ( ) : The shock ignition pressure amplification and the spherical effect are well-described by the Guderley model Von Guderley.G, Luftfahrt-Forsch, 9, 302, (1942) Centre Lasers Intenses et Applications, Université Bordeaux 1- CNRS - CEA Shock ignition : modelling elements and target robustness M. Lafon, X. Ribeyre and G. Schurtz FWHM (ps) ΔT (ps) E abs (kJ) E TN (MJ) 5003004019 4002003218 3001002417 250502016 If spike duration decreases about 50%, thermonuclear energy only decreases about 15% Ignition pulse robustness Standart impulsion duration Spike power time shape t Ps Ps/2 TT TRTF Laser time rise : TR =TF = 200 ps Pulse duration at FWHM : TM+ΔT+TD The spike power remains constant : P S =cte The ignition mainly depends on the spike power and not on the spike energy Compression laser energy (kJ)2585180312600 Parameter h0.50.811.21.5 Target Mass (mg)0.070.280.591.02.0 Threshold absorbed spike power (TW) 67768697118 Absorbed spike intensity (10 15 W/cm²) 165.642.82 Compression areal density (g/cm²)0.81.181.341.61.9 Thermonuclear energy (MJ)18173880 Shock ignition performance domain 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 < V imp (km/s) < 290 Conclusions and prospects 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 HIPER target shock ignition robustness 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) Compression : 180 kJ into 10 ns (50TW) Ignition : 80 kJ into 500 ps (150TW) + E TN =20 MJ Gain = 80 Iso-thermonuclear energy curves 250ps Ignition pulse Compression pulse For all targets : Laser Gain model Référence 522µm814µm 1044µm 1250µm1570µm 5 mg 1 mg 0,5 mg 0,1 mg 0,01 mg Rosen model CHIC simulations 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 defining the hot spot at ignition instant: Fuel mass shell adiabat at stagnation coupling efficiency between the laser energy and the internal DT fuel energy 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 Intensity (10 15 W/cm²) Parametric instabilities Hydrodynamic instabilities P L =110TW P L =340TW P L =130TW h = 0,5 h = 1 h = 2 Mass=0,59mg Simple, spherical and scalable target The laser type required is the same for both compression and ignition stages 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) HIPER target ρ sh P hs r HS r SH P sh ρ hs Hot Spot Shell Hot spot ignition condition : The self-heating condition for non-isobaric case can be written as : The hot spot enters the ignition domain with specific values of and which depends on the fuel non isobaric parameter ε When : isobaric configuration Shock launching time Absorbed spike power