The Pursuit of Indirect Drive Ignition at the National Ignition Facility

Transcription

1 The Pursuit of Indirect Drive Ignition at the National Ignition Facility Workshop on Plasma Astrophysics: From the Laboratory to the Non-Thermal Universe Oxford, England July 3-5, 2017 Richard Town Deputy ICF Program Leader This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA Lawrence Livermore National Security, LLC

2 Central hot spot inertial confinement fusion Heating P PdV ~ Pr v / R Massive imploding shell heats central hot spot by PdV v Hot DT Cold dense DT 2

3 Central hot spot inertial confinement fusion Heating P PdV ~ Pr v / R v => D +T n( 14.1MeV ) + 4 He( 3.5MeV ) P Fus ~ n 2 T 4 a Hot DT rr HS 4 He deposit energy in hot spot if rr HS > 0.2 g/cm 2 Cold dense DT *rr = Areal density 3

4 Central hot spot inertial confinement fusion Heating > Cooling => Ignition P PdV ~ Pr v / R v P Fus ~ n 2 T 4 P Rad ~ n 2 T 1/2 P e ~ T 7/2 / R 2 e - Ideal ignition T ~ 4 kev (Fusion power > rad power) a Hot DT rr HS In practice need higher T Cold dense DT *rr = Areal density 4

5 Once the hot spot ignites, a burn wave rapidly heats the rest of the fuel to fusion temperature f burnup ρr ρr + 6 (g/cm 2 ) for total rr ~ 2 g/cm 2 f burnup 25% 5

6 If the fuel ignites well on the NIF. Cold DT shell ~ 1000 g/cm 3 Energy released ~ 20 MJ ~ 1 Kg of coal a 50 million degrees ~ 100 g/cm 3 Pressure ~ 350 Gbar rr ~ 1.5 g/cm 2 How do we create such conditions? ~0.1 mm 6

7 The United States national inertial confinement fusion (ICF) program is pursuing 3 approaches Laser Indirect Drive LLNL NIF Laser Direct Drive Univ. Rochester (OMEGA, NIF) Magnetic Direct Drive Sandia Nat l Lab Z-machine Spherical on Omega Most stable Better coupling Instability limits Convergence Technology efficient, scalable Instability limits Convergence and velocity Magnetizes fuel/burn products 7

8 Today we will talk about laser indirect drive on the NIF Laser Indirect Drive LLNL NIF Laser Direct Drive Univ. Rochester (OMEGA, NIF) Magnetic Direct Drive Sandia Nat l Lab Z-machine Spherical on Omega Most stable 8

9 9

10 10

11 400 MJ: stored energy in capacitor banks 2 MJ: laser light 10 MJ: Stored in amplifiers 11

12 OFFICIAL USE ONLY 2 MJ: laser light 150 kj: capsule 15 kj:fuel 12 12

13 Special shrouds keep the target at 290 degrees 13

14 1 cm 14

15 X-ray picture of capsule taken down axis of the hohlraum just before a shot 2mm diameter capsule 15

16 Plastic Ignition Capsule 195 µm ~2 mm diameter 16

17 The challenge near spherical implosion by ~35X 195 µm DT shot N Bang Time (less than diameter of human hair) ~2 mm diameter 17

18 After the shot 18

19 Major challenge: drive symmetry at velocity and convergence needed for ignition not yet predictive Early foot End of foot Start of main End of main 19

20 The capsule must be designed and driven to withstand hydro instabilities reasonably predictive 20

21 The capsule must be designed and driven to withstand hydro instabilities reasonably predictive 21

22 The capsule must be designed and driven to withstand hydro instabilities reasonably predictive 22

23 The capsule must be designed and driven to withstand hydro instabilities reasonably predictive 23

24 Achieving ignition conditions requires understanding and controlling the implosion properties α Entropy rr DT ~ 1.45 g/cm 2 V DT ~ 370 km/s Velocity V High compression for rr trap alphas, and confinement Hot e- Ablator DT Ice PdV work to heat hot spot DT Hot spot R HS ΔR HS Conductive and radiative cooling Efficient conversion of implosion KE to hot spot thermal energy M Mix RMS hot spot shape < 10% Shape S 24

25 This talk describes the main scientific results from experiments on NIF National Ignition Campaign Establish the capability to do controlled implosions High Foot campaign Explore more stable implosions Engineering features Alternate ablators Safe hohlraums Coupling more energy 1D implosion Lower LPI More spherical implosions Advanced hohlraums Scaling studies 25

26 The national ignition campaign developed platforms to measure implosions and tune the implosion α Entropy Velocity V VISAR interferometry Hot e- X-ray Power X-ray Backlit Imaging Ablator DT Ice Keyhole DT Hot spot R HS Convergent Ablator/ConA Ge Spectra, Continuum emission ΔR HS X-ray or neutron core image DT Symcap M Mix Shape S 26

27 Most requirements were met individually α Entropy rr DT ~ 1.45 g/cm 2 V DT ~ 370 km/s Velocity V rr ~ g/cm 2 Hot e- Ablator DT Ice V fuel ~ km/s DT Hot spot R HS ΔR HS RMS hot spot shape < 10% But variable M Mix RMS hot spot shape < 10% Shape S 27

28 NIC implosions reached ignition-relevant ρr 1.3 g/cm 2, but neutron yields were < HF T0 As laser energy was added to increase velocity, performance degraded Neutron Yield Laser Energy (MJ) 28

29 NIC implosions reached ignition-relevant ρr 1.3 g/cm 2, but neutron yields were < HF T0 Neutron Yield Laser Energy (MJ) Hydrodynamic instabilities turned out to be the biggest problem 29

30 A more stable high foot laser pulse was developed Laser power (TW) Laser pulses for NIC (low-foot) and high-foot designs Reduced growth of the Rayleigh Taylor instability at the ablation front Reduced implosion convergence ratio CR = R ablator,outer R hot spot Time (ns) N low-foot N high-foot The high-foot design trades better stability for lower ρr and ultimate fusion gain 30

31 Experimental measurements of Rayleigh Taylor growth confirmed the stability of the high-foot Lo-Foot vs Hi-Foot Growth factor at 650 µm 1200 Ripple target X-ray snapshots Optical Depth Growth Factor Simulation High foot Low foot Mode Number Radiation hydrodynamic calculations of RT growth factors are very close to data: Predictive capability for growth is OK: problem is the RT growth seed 31

32 In contrast with the low-foot NIC design, the high-foot yield increased at higher velocity HF T Equator Pole DU Neutron Yield Laser Power (TW) Laser Energy (MJ) Time (ns) 32

33 By using thinner ablators the design could be pushed to high velocities and stagnation pressures HF T0 HF T 1 HF T HF T0 HF T 1 HF T Neutron Yield Pressure (Gbar) Laser Energy (MJ) Coast time (ns) 33

34 When the velocity of thinner shells was increased, the yield dropped a cliff HF T0 HF T 1 HF T HF T0 HF T 1 HF T Neutron Yield Pressure (Gbar) Laser Energy (MJ) Coast time (ns) 34

35 As velocity increased, yield dropped relative to 1D predictions; 2D predictions were closer 1D Sim 2D Sim 100% 35% 10% % Experimental Yield 340 km/s 375 km/s km/s Simulated Yield Faster high-foot implosions with thinner shells have similar distortions to NIC implosions 35

36 We know of two major issues Asymmetric x-ray drive + Processed in-flight radiograph Simulated DT fuel at stagnation Tent Tent Tent capsule tent But there are important knowledge gaps (e.g. cannot see the shell) and the model is not perfect and these may be masking other factors e.g hydro instability 36

37 The tent alternative project considered a wide range of possible options Fill-tube only Cantilevered fill-tube Fishing pole Tetra-cage Eliminated Fill-tube is larger diameter fill-tube is cantilevered wires parallel to page supported by additional component supported by additional component wires perp to page Block foam support Foam shell support Near-tangential tent, standard formvar Polar contact with disk or C re-inforced PI tent thin HDC disk MItigated low-density (3 mg/cc) foam low-density (~30 mg/cc) foam requires 4-part hohlraum to ensure tangential contact 37

38 Including levitation (magnetic) but not as a near term project! -I +I Note capsule Push-Pull -I +I -I +I 38

39 We have tested many concepts to measure the growth using the HGR platform 30-μm thick fill tube Cantilevered fill tube SiO 2 foam-shell 10 μm fill tube 30 μm fill tube 10 μm fill tube 30 μm fill tube 300 μm offset Amplitude Δ(OD) μm 30 nm tent 200 μm offset 600 μm 658 μm

40 We have been eliminating support options and will test remainder in layered implosions this year Fill-tube only Cantilevered fill-tube Fishing pole Tetra-cage Eliminated Fill-tube is larger diameter fill-tube is cantilevered wires parallel to page supported by additional component supported by additional component wires perp to page Block foam support Foam shell support Near-tangential tent, standard formvar Polar contact with disk or C re-inforced PI tent MItigated low-density (3 mg/cc) foam low-density (~30 mg/cc) foam requires 4-part hohlraum thin HDC disk to ensure tangential contact 40

41 The hohlraum challenge: NIF scale ICF hohlraums fall roughly into two categories different challenges High gas fill LPI dominated CBET Low gas fill rad hydro dominated Inner beam SRS 2w p Low efficiency, strong time dependent drive asymmetry 41

42 The hohlraum challenge: NIF scale ICF hohlraums fall roughly into two categories different challenges High gas fill LPI dominated CBET Low gas fill rad hydro dominated Inner beam SRS 2w p Low efficiency, strong time dependent drive asymmetry eliminate LPI More efficient Better symmetry, more predictable? Growing evidence low gas-fill hohlraums behave more like simulations 42

43 Te - growing evidence low fill hohlraums behave more like simulations than LPI dominated hohlraums Te (kev) 4 3 Measured and simulated T e MnHe α (y+w) Simulatied T e at measured trajectory Only a few measurements to date Not yet predictive Pulse Shape Time (ns) MnLya/MnHea Dot Z Position (μm) Simulation Measurement 0.6Dot mg/cc, Trajectory 2-shock HDC 2-shk HDC He gas fill, 0.6mg/cc Time (ns) 43

44 Physics of the inner beams is complicated makes controlling and predicting symmetry challenging Complicated beam path, time dependent energy deposition distributed in space High Z bubble eventually shuts off inner beams loss of control Ultimately need the right x-ray production over the waist, also complicated Gold/High Z bubble NLTE e-trans NLTE e-trans db/dt e-trans Inner beam Mix (hydro, kinetics) Motivates larger hohlraums and shorter pulses 44

45 We have developed new experiments to quantify how well the inner beam makes it to the waist Thin-walled hohlraum 4.8 ns 5.2 ns 5.5 ns 6.2 ns Innercone only Inner beams Combined with existing symmetry measurements Symmetry control, predictable* Losing symmetry control, predictability 45

46 Bigger hohlraums make things simpler (and easier?) but practical limit Better for symmetry Better for laser 46

47 capsule$for$2$and$4$shock$$dd$ HDC s high density (3.5 g/cm3 compared to 1 g/cm3 for CH) results in shorter laser pulses that(b)$1mm$radius$hdc$capsules$ are easier to fit into the mcaps$/$1dcona$ hohlraum 4 outer#radius#1086#or#1076#µm# 2 Laser power (TW) HDC#ablator#86#or#76#µm#thick# 3.32#g/cc# DD##or#DT#gas# 3.2#or#7#mg/cc# Time (ns) N low-foot N step HDC with$thd$ice$layer$ N high-foot (d)$si$doped$$ch$rev$5$$symcap$ 47

48 Improved drive symmetry -> more efficient implosions -> higher yield with less energy Neutron Yield CH LF CH HF HDC SC HDC High foot 2015 NIC Laser Energy (MJ) Key was eliminating LPI Round implosions Better agreement with code YOC1D ~ 30-40% 48

49 By scaling-up the HDC design we recently increased the yield above for the first time Neutron Yield CH LF CH HF HDC SC N HDC N High foot 2015 NIC Laser Energy (MJ) Ignition (with G>1 at NIF) Q a ~2-3 alpha dominated (~120 kj) Q a ~1 burning plasma (~50kJ) Alpha-heating (HDC, 2017) (high foot, 2014/15) (NIC, 2012) (March 2011) c (Energy for ignition ~ 1/c 2 ) 49

50 The best we ve done on a single shot is about ~2X from ignition Cold DT shell ~ 1000 g/cm 3 Best performance on single shot ~ 500 g/cc Energy released ~ 47kJ ~ 2 g of coal a 50 million degrees ~ 100 g/cm 3 Pressure ~ 350 Gbar rr ~ 1.5 g/cm 2 ~ 5 kev ~ 40 g/cc ~ 200 Gbar ~ 0.8 g/cm 2 ~0.1 mm 50

51 2020 deliverable if ignition not achieved quantitative scaling and UQ from highest performance reasonably achievable 1 MJ Neutron Yield kj 10 kj Quality (faster, denser, rounder, cleaner) Energy (Bigger) Data (high foot, Increasing velocity) 2020 goal: 1. Is ignition possible on the NIF quality? Have to measure and understand limiters 2. If not, how much more energy is needed? Validated predictive capability + UQ 1.8 MJ Laser Energy 51

52 Collaborators M. J. Edwards, O. A. Hurricane, W. W. Hsing, P. K. Patel, L. F. Berzak Hopkins, M. A. Barrios, L. Benedetti, D. K. Bradley, D. A. Callahan, D. T. Casey, P. M. Celliers, C. J. Cerjan, D. S. Clark, E. L. Dewald, L. Divol, T. Döppner, J. E. Field, G. P. Grim, S. W. Haan, G. N. Hall, B. A. Hammel, M. Hermann, D. E. Hinkel, D. D. Ho, M. Hohenberger, N. Izumi, O. S. Jones, R. L. Kauffman, S. F. Khan, A. L. Kritcher, O. L. Landen, S. LePape, T. Ma, A. J. MacKinnon, A. G. MacPhee, M. M. Marinak, L. Masse, P. Michel, N. B. Meezan, J. L. Milovich, J. D. Moody, A. Moore, D. H. Munro, A. Nikroo, A. Pak, H. S. Park, J. L. Peterson, H. R. Robey, M. D. Rosen, J. S. Ross, J. D. Salmonson, M. B. Schneider, V. A. Smalyuk, B. K. Spears, P. T. Springer, M. Stadermann, D. J. Strozzi, C. A. Thomas, R. Tommasini, B. Van Wonterghem, C. R. Weber Lawrence Livermore National Laboratory, Livermore, California 94551, USA J. L. Kline, and S. Batha Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA 52

53 53

54