High-Gain Direct-Drive Shock Ignition for the Laser Megajoule

High-Gain Direct-Drive Shock Ignition for the Laser Megajoule: prospects and first results. 100 Density at stagnation FCI 2 Direct Drive @ 2 rings 50 B. Canaud CEA, DAM, DIF France CEA-DAM Ile-de-France 50 Radius (µm) 100 7 th Workshop Direct Drive and Fast Ignition May, 3 -6, 2009 Prague, 1

Collaborators X. Ribeyre, M. Lafon, J. L. Feugeas, J. Breil, G. Schurtz CELIA, Bordeaux M. Temporal, R. Ramis ETSIA, Madrid, Spain CEA-DAM Ile-de-France 2

Standard LMJ direct drive illumination differs from indirect one by a more isotropic beam layout on the target chamber. a) Baseline LMJ Direct Drive 33. 2° (10 beams) Z DD Z 59. 5° (10 beams) DT ID b) LMJ Indirect Drive 33. 2° 49° 59. 5 ° 78° 102° 120. 5° 131° 146. 8° CEA-DAM Ile-de-France DT 33. 2° (10 beams) 49° (10 beams) 59. 5° (10 beams) 78° (10 beams) Quad Each LMJ beamlet is limited by its power max: Pmax ≤ 2. 5 TW. 3

A few years ago, we proposed a new direct drive configuration with indirect drive beam layout [*]… a) Baseline LMJ Direct Drive b) LMJ Indirect Drive 33. 2° (10 beams) Z 59. 5° (10 beams) DT DT 33. 2° (10 beams) 49° (10 beams) 59. 5° (10 beams) 78° (10 beams) … but with only 1. 2 MJ of laser energy. CEA-DAM Ile-de-France (*) Canaud B. et al, Plasmas Phys. Cont. Fusion, 49, B 601 (2007). 4

A new 2 -rings baseline(*) high-gain Direct-Drive design has been proposed with focal spot zooming. 1 µm CH Wetted foam 165 µm 1341 µm DT ice 134 µm DTgas Z 49° (45%) 59. 5° (55%) Focal spot zooming increases laser-target coupling narrow efficiency[**]. spot early time large spot late time 1 beam large, 3 narrows on each quad. 100 Adiabat = 3. 5 V=4. 105 m/s Density at stagnation FCI 2 Direct Drive @ 2 rings 50 (**) Canaud B. et al, Nucl. Fus. , 45, L 43 (2005) With zooming and 2 rings, Gain=32 with 1 MJ laser. 50 Radius (µm)100 CEA-DAM Ile-de-France (*) Canaud B. et al, Nucl. Fus. , 47, 1642 (2007) 5

Without zooming, the target is marginally igniting. Thermonuclear gain 100 Adiabat = 3. 5 V=4. 105 m/s LMJ design with zooming 10 Homothetic target family curve LMJ design without zooming 1 w/o Zooming w/ Zooming 0. 1 : adiabat v : implosion velocity CEA-DAM Ile-de-France 0. 4 0. 6 1 3 Laser energy (MJ) with 3 D ray-tracing 6

Alternative exists to displace the energy threshold towards lower energies, keeping constant the implosion target parameters ( , v). • Isobaric ignition concerns standard direct drive ignition. Piso T Burn of DT fuel Isobaric Ignition threshold Hot-spot DT fuel radius Burn of Hot spot : adiabatic parameter v : implosion velocity • Non-isobaric ignition reduces the energy threshold for ignition. Pnon iso Piso T where Hot spot DT fuel radius CEA-DAM Ile-de-France (*) Betti R. et al, Phys. Rev. Lett. , 98, 155001 (2007) 7

Non isobaric conditions can be achieved by launching a strong shock at the end of the implosion. • A low-isentrope compression is obtained by a usual pulse shape. • An additional spike launches a strong shock in the target. Pspike tspike CEA-DAM Ile-de-France 8

Shock can be created by the 33°-ring of the LMJ(*). Z DT 33. 2° (10 beams) 49° (10 beams) 59. 5° (10 beams) } 2 D CHIC simulations of bipolar shock ignition show a good sphericity of the ignitor shock. CEA-DAM Ile-de-France (*) Ribeyre X. et al, Plasmas Phys. Cont. Fusion, 51, 015013 (2009). 9

Fast-ignitor (*) targets can be considered for Shock Ignition (+). Hi. PER(*) baseline target DTgas 1040 µm 1 D implosion data Absorbed energy Adiabat Implosion velocity Density Max Areal density max Pspike 300 ps 30 200 ps 20 110 k. J 1 290 km/s 600 g/cm 3 1. 5 g/cm 2 • The target is far below the ignition threshold. 200 ps 10 t (ns) tspike 10 200 Pspike (TW) DT ice 210 µm @ 250 kg/m 3 50 P (TW) 40 100 P=180 TW ETh=20 MJ 9. 5 CEA-DAM Ile-de-France tspike 10 10. 4 (*) Ribeyre X. et al, Plasmas Phys. Cont. Fusion, 50, 025007 (2008). (+) Ribeyre X. et al, Plasmas Phys. Cont. Fusion, 51, 015013 (2009) 10

Marginally igniting standard direct drive target can be triggered by shock ignition (SI). 1 µm CH Wetted foam 120 µm 960 µm DT ice 100 µm DTgas Ethermonuclear(MJ) 100 10 P (TW) 150 Pspike 300 ps 100 Baseline Direct Drive = 3. 5 V=400 km/s 200 ps 50 t (ns) 7 1 D implosion data Absorbed energy Density Max Areal density max With SI (@max) Pspike Density Max Areal density max Eth With Shock ignition 1 tspike 200 k. J 500 g/cm 3 1. g/cm 2 190 TW 1700 g/cm 3 1. 27 g/cm 2 11 MJ 0, 1 0, 01 E CEA-DAM Ile-de-France kinetic (MJ) 0, 1 With the spike and 2 rings, G 1 D=50 with 0. 2 MJ absorbed laser. 11

Different targets from the FI-family should be considered for LMJ. 100 KJ-absorbed 200 KJ-absorbed 500 KJ-absorbed 1040 µm DT gas 250 µm DT ice DT gas 2090 µm 1750 µm 1240 µm 210 µm DT ice 850 KJ-absorbed 350 µm DT ice DT gas 420 µm DT ice DT gas =1 v = 290 km/s max= 600 g/cm 3 1 D implosion data Absorbed energy 100 k. J r 1. 2 g/cm 2 1 D implosion data Absorbed energy 200 k. J r 1. 6 g/cm 2 1 D implosion data Absorbed energy 500 k. J r 2 g/cm 2 1 D implosion data Absorbed energy 850 k. J r 2. 24 g/cm 2 Spike Laser Power max 120 TW Abs Intensity 6 e 15 W/cm 2 Spike Laser Power 160 TW Abs Intensity 5 e 15 W/cm 2 Spike Laser Power max 110 TW Abs Intensity 2 e 15 W/cm 2 Spike Laser Power 100 TW Abs Intensity 1 e 15 W/cm 2 Thermonuclear rho r 1. 7 g/cm 2 Energy Th. 18 MJ Thermonuclear rho r 2 g/cm 2 Energy Th. 44 MJ Thermonuclear rho r 2. 2 g/cm 2 Energy Th. 133 MJ Thermonuclear rho r 2. 4 g/cm 2 Energy Th. 260 MJ CEA-DAM Ile-de-France 12

The power in the spike is a key parameter for SI. 100 KJ-absorbed 200 KJ-absorbed 1240 µm 210 µm DT ice 1040 µm DT gas 250 µm DT ice DT gas =1 v = 290 km/s max= 600 g/cm 3 1 D implosion data Absorbed energy 100 k. J r 1. 2 g/cm 2 1 D implosion data Absorbed energy 200 k. J r 1. 6 g/cm 2 Spike Laser Power max 120 TW Abs Intensity 6 e 15 W/cm 2 Spike Laser Power 160 TW Abs Intensity 5 e 15 W/cm 2 Thermonuclear r 1. 7 g/cm 2 Energy Th. 18 MJ Thermonuclear r 2 g/cm 2 Energy Th. 44 MJ CEA-DAM Ile-de-France Need between 200 and 300 TW for ignitor pulses : The 33° rings will produce only 200 TW We need to redefine a target design and to improve the lasertarget coupling efficiency for the ignitor pulses. 13

Low energy for fuel assembly should allow to use only the 49° ring. 100 KJ-absorbed 200 KJ-absorbed 1240 µm 210 µm DT ice 1040 µm DT gas 250 µm DT ice DT gas b) LMJ Indirect Drive Z DT 33. 2° 49° 59. 5° =1 v = 290 km/s max= 600 g/cm 3 1 D implosion data Absorbed energy 100 k. J r 1. 2 g/cm 2 1 D implosion data Absorbed energy 200 k. J r 1. 6 g/cm 2 Spike Laser Power max 120 TW Abs Intensity 6 e 15 W/cm 2 Spike Laser Power 160 TW Abs Intensity 5 e 15 W/cm 2 Thermonuclear r 1. 7 g/cm 2 Energy Th. 18 MJ Thermonuclear r 2 g/cm 2 Energy Th. 44 MJ CEA-DAM Ile-de-France We need more than 200 k. J to assemble the target: the 49° rings should be a good candidate. We need to improve the irradiation uniformity. 14

Summary High gain direct drive Shock ignition on LMJ requires to address several physical key issues. • Standard direct drive fuel assembly is achievable with a part of X drive beams (rings @ 49° et 59° 5). • Using the ring @ 49° needs well characterize and to improve (if necessary) the irradiation uniformity (PDD, Green House Target, …) • Shock ignition with the last beams (rings @ 33°) should be possible but we may need to redefine a target with lower power ignitor. • Extremely high gains could be achieved on LMJ : E 1 D absorbed~ 0. 2 MJ, Eth ~ 40 MJ In addition, to be done … • 1 D design must be revisited (wetted foam, reduced IFAR, …). • Fully 2 D calculations (with ray-tracing 3 D) have to be done for LMJ. Restrictions • Parametric instabilities driven by the shock ignitor could be problematic. • Hydrodynamic stability of the capsule must be addressed • Unknown Physics (eos, heat conductivity, kinetic effects, …) could be limiting. • … CEA-DAM Ile-de-France 15