The Pursuit of Indirect Drive Ignition at the National Ignition Facility

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-AC52-07NA27344. Lawrence Livermore National Security, LLC

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

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

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

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

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

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

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

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

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

Special shrouds keep the target at 290 degrees 13

1 cm 14

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

Plastic Ignition Capsule 195 µm ~2 mm diameter 16

The challenge near spherical implosion by ~35X 195 µm DT shot N120716 Bang Time (less than diameter of human hair) ~2 mm diameter 17

After the shot 18

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

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

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

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

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

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

This talk describes the main scientific results from experiments on NIF 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 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

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

Most requirements were met individually α Entropy rr DT ~ 1.45 g/cm 2 V DT ~ 370 km/s Velocity V rr ~ 1.2-1.3 g/cm 2 Hot e- Ablator DT Ice V fuel ~ 350-370 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

NIC implosions reached ignition-relevant ρr 1.3 g/cm 2, but neutron yields were < 10 15 10 16 HF T0 As laser energy was added to increase velocity, performance degraded Neutron Yield 10 15 130501 111215 120131 110908 110914 120205111112 110904 120920 120417 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Laser Energy (MJ) 28

NIC implosions reached ignition-relevant ρr 1.3 g/cm 2, but neutron yields were < 10 15 10 16 HF T0 Neutron Yield 10 15 130501 111215 120131 110908 110914 120205111112 110904 120920 120417 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Laser Energy (MJ) Hydrodynamic instabilities turned out to be the biggest problem 29

A more stable high foot laser pulse was developed Laser power (TW) 100 10 4 2 6 4 2 6 4 2 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 1 0 5 10 Time (ns) 15 20 N120321 low-foot N130812 high-foot The high-foot design trades better stability for lower ρr and ultimate fusion gain 30

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 1000 800 600 400 200 0-200 Simulation High foot Low foot 0 40 80 120 160 200 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

In contrast with the low-foot NIC design, the high-foot yield increased at higher velocity 10 16 HF T0 140120 140304 Equator Pole 140511 131119 DU 130927 Neutron Yield 10 15 130501 130710 130812 Laser Power (TW) 500 400 300 200 100 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Laser Energy (MJ) 0 0 5 10 15 20 Time (ns) 32

By using thinner ablators the design could be pushed to high velocities and stagnation pressures 10 16 HF T0 HF T 1 HF T 1.5 150211 150401 140520 150409 150121 140311 140120 140304 140511 131119 300 250 HF T0 HF T 1 HF T 1.5 140707 130927 140520 Neutron Yield 131219 140225 141106 130812 Pressure (Gbar) 200 150 100 150121 150401 150409 150211 140707 14051140304 140120 140311140225 131119 131219 141106 130927 130812 130710 10 15 130501 50 130710 130501 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Laser Energy (MJ) 0 0 0.5 1 1.5 2 2.5 Coast time (ns) 33

When the velocity of thinner shells was increased, the yield dropped a cliff 10 16 HF T0 HF T 1 HF T 1.5 150211 150401 140520 150409 150121 140819 140311 140120 140304 140511 131119 300 250 HF T0 HF T 1 HF T 1.5 140707 130927 140520 Neutron Yield 131219 140225 141106 130812 Pressure (Gbar) 200 150 100 140819 150121 150401 150409 150211 140707 14051140304 140120 140311140225 131119 131219 141106 130927 130812 130710 10 15 130501 50 130710 130501 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Laser Energy (MJ) 0 0 0.5 1 1.5 2 2.5 Coast time (ns) 34

As velocity increased, yield dropped relative to 1D predictions; 2D predictions were closer 1D Sim 2D Sim 100% 35% 10% 10 16 1% Experimental Yield 340 km/s 375 km/s 10 15 300 km/s 10 15 10 16 10 17 10 18 Simulated Yield Faster high-foot implosions with thinner shells have similar distortions to NIC implosions 35

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

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

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

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) +0.2 +0.1 0.0-0.1 600 μm 30 nm tent 200 μm offset 600 μm 658 μm -0.2 39

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

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

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

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 2 1 0 Pulse Shape 5 6 7 8 Time (ns) MnLya/MnHea Dot Z Position (μm) 3500 3000 2500 2000 Simulation Measurement 0.6Dot mg/cc, Trajectory 2-shock HDC 2-shk HDC He gas fill, 0.6mg/cc 1500 3 4 5 6 7 Time (ns) 43

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

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

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

capsule$for$2$and$4$shock$$dd$ HDC s high density (3.5 g/cm3 compared to 1 g/cm3 for CH) results in shorter laser pulses that(b)$1mm$radius$hdc$capsules$ are easier to fit into the mcaps$/$1dcona$ hohlraum 4 outer#radius#1086#or#1076#µm# 2 Laser power (TW) 100 8 6 HDC#ablator#86#or#76#µm#thick# 3.32#g/cc# 4 2 10 DD##or#DT#gas# 3.2#or#7#mg/cc# 8 6 4 2 1 0 5 10 15 20 Time (ns) N120321 low-foot N141019 3-step HDC with$thd$ice$layer$ N130812 high-foot (d)$si$doped$$ch$rev$5$$symcap$ 47

Improved drive symmetry -> more efficient implosions -> higher yield with less energy Neutron Yield 10 16 10 15 10 14 CH LF CH HF HDC SC HDC 2017 151102 160418 160313 160120 160223 170226 161023 161113 130501 130331 111103 130710 111215 120131 110908 130530 120205 111112 110914 130802 110904 120920 110615 110620 120417 120321 120219 120126 120802 110608 110826 120808 140707 170601 131219 141016 140225 141106150610 130812 120316 120311 120405 120213 120626 120422 140120 140304 150211 140520 150409 150121 140511 150401 150528 140311 160829 140819 131119 160509 150218 150318 141008 130927 160807 High foot 2015 NIC 2012 120412 120716 120720 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Laser Energy (MJ) Key was eliminating LPI Round implosions Better agreement with code YOC1D ~ 30-40% 48

By scaling-up the HDC design we recently increased the yield above 10 16 for the first time Neutron Yield 10 16 10 15 10 14 CH LF CH HF HDC SC N170226 HDC 2017 151102 160418 160313 160120 160223 170226 161023 161113 130501 130331 111103 130710 111215 120131 110908 130530 120205 111112 110914 130802 110904 120920 110615 110620 120417 120321 120219 120126 120802 110608 110826 120808 140707 170601 131219 141016 140225 141106150610 130812 120316 120311 120405 120213 120626 120422 N170601 140120 140304 150211 140520 150409 150121 140511 150401 150528 140311 160829 140819 131119 160509 150218 150318 141008 130927 160807 High foot 2015 NIC 2012 120412 120716 120720 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 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

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

2020 deliverable if ignition not achieved quantitative scaling and UQ from highest performance reasonably achievable 1 MJ Neutron Yield 10 17 10 16 10 15 100 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

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

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