1 Inertial Fusion Energy with Direct Drive and Krypton Fluoride (KrF) Lasers Presented by: John Sethian Plasma Physics Division U.S. Naval Research Laboratory Co authors: S. P. Obenschain, A. J. Schmitt, J. Weaver, V. Serlin, R. H. Lehmberg, M. Karasik, J. Oh, J. W. Bates, Y. Aglitskiy, D. Kehne, M. Wolford, F. Hegeler, M. Myers, E. Mclean, W. Manheimer, A. L. Velikovich, L. Y Chan, and S. Zalesak Presented at the 24 th International Atomic Energy Agency Conference on Fusion Energy San Diego, CA October 11, 2012 Work supported by the U.S. Department of Energy, NNSA.

2 Simplicity and Performance (Gain) We believe that the two key factors for practical IFE (or any approach to Fusion) are: Simplicity and Performance (Gain) Fusion is hard: Better to start with a simpler, higher performance approach Gives contingency for reality Corollary: Much easier to get simplicity & performance by choice of approach Rather than depending on engineering or physics advances later

3 Symmetric Direct Drive Targets Laser Beams Pellet Efficient illumination geometry…laser directly illuminates target Simplest targets to fabricate and recycle Easier to understand physics than other approaches Highest predicted performance: Gain > 1 MK KrF Laser

4 KrF Lasers have inherent advantages for fusion energy  Most uniform laser beam Helps achieve smooth implosions  Shortest UV (248 vs 351 nm) Better coupling to target Higher ablation pressures Higher threshold Laser Plasma Instabilities  Target can be driven faster  "Zoom" (decrease spot as pellet implodes)  Gas Medium...easy to cool, durable  Mostly robust industrial technology Nike single beam focus  beam dia  time  PHYSICS: High Gain POWER PLANT: Attractive Technology

5 Shock Ignition: Shell accelerated to sub-ignition velocity (<300 km/sec), Ignited by converging shock produced by high intensity spike Main Drive  1.5 x W/cm 2 First Shock Ignition Theory: Betti et al, Phys. Rev. Lett. 98, (2007). Picket Pulse Foot Ignition Spike  W/cm 2

6 KrF Direct Drive Target designs predict power plant class gains at laser energies  1 MJ Target Gain Laser Energy (MJ) “Fast Compression” KrF Direct Drive Shock Ignition Solid State (351 nm) Two focal zooms during implosion  G = 10* Shock Ignition KrF (248 nm) *Gives Recirculating power = 25% > Laser efficiency =  KrF = 7.0% > Thermal efficiency  = 40% > Blanket Burnup =  = 1.1

7 High resolution 2-D simulations show shock ignition designs robust to hydro instabilities 521 kJ laser 2D Gain = 102 1D gain = 142

8 Observed Rayleigh Taylor growth agrees with 2 D FAST simulations Mass variation (mg/cm 3 ) time (ns) X-Ray images of rippled Foam/liquid D 2 targets 2 D FAST simulations

9 In accordance with theory, the intensity threshold for LPI is higher for a KrF (248 nm) than a solid state (351 nm) laser Predicted Threshold (simpler EM plane wave analysis): I threshold (2  ) = I (x W/cm 2 ) ~ 80 T keV /(  n  L  m ) Both experiments, which determine onset of 2  agree with this! Omega (solid state laser) I thershold ~  W/cm 2 Stoeckl, et al., Phys. Rev. Lett (2003), J. Weaver, Bull. Amer. Physics Soc., 54 No. 15, JO5.8 (2009). Nike (KrF laser) I thershold ~  W/cm 2 pe L  m = 120 nm scale length

10 Progress in KrF laser Development NRL Electra KrF Laser J/pulse 2.5 – 5 Hz

11 Laser Gas Recirculator Laser cell (Kr+F 2 +Ar) Input Laser (Front end) Elements of a Krypton Fluoride (KrF) electron beam pumped gas laser Window KrF laser Physics e-beam window (hibachi) electron beam Cathode Pulsed power Energy + ( Kr+ F 2 )  ( KrF)* + F  Kr + F 2 + h ( = 248 nm) Typical e-beam: ,000 kV, 100 -to 500 kA, 150 – 250 ns, 3000 – 12,000 cm 2

12 Electra KrF Laser capable of 100,000 pulse continuous runs Electra Cell after 30,000 shot continuous laser run Electron beam window Electron beam window electron beam Gas Flow LASER 90,000 laser shots (10 hrs) 2.5 Hz 150,000 laser shots on same 2.5 Hz 50,000 laser shots on same 5 Hz 300,000 laser shots in 8 days of operation

13 Reproducibility with Efficiency maintained independent of rep-rate (1 Hz and 2.5 Hz)

14 All Solid State Pulsed Power demonstrator Continuous run: 11.5 M 10 Hz (319 hrs) PLEX, LLC 200 kV, 4.5 kA, 250 ns, Marx > 80% efficiency Marx Pulse Forming Line Load Magnetic Switch

15 Orestes KrF Physics Code accurately predicts Electra Main Amplifier Laser Pulse time (nsec) P e-beam (expt) I Laser (expt) I Laser (Orestes) input e-BEAM Power (GW) output LASER Power (GW) Total laser energy 730 Joules

16 Based on our experiments, an IFE KrF system wall plug efficiency > 7% Pulsed PowerShown solid state demo82% (wall plug- flat top e-beam) HibachiNo Anode, Pattern Beam81% (e-beam in diode into gas) KrFElectra Experiments12% (e-beam to laser) (literature  14%) Optics to targetEstimate95% AncillariesPumps, recirculator95% Total7.1% For fusion energy want  G > 10. with KrF and advanced targets:  G = 7.1% x 300 ~ 21

17 Summary: Inertial Fusion Energy with Direct Drive & Krypton Fluoride (KrF) Lasers Relative Simplicity Targets: Physics, Illumination Geometry, Target Fabrication KrF Laser: Gas laser pumped with e-beams Performance: KrF lasers have advantages (short wavelength, uniformity) Simulations: Power Plant class gains (>200)with KrF Laser < 1 MJ Target physics experiments: Benchmark simulation codes backed with experiments Are showing advantages of KrF KrF Laser: Based on experiments, predict sufficient efficiency Developing S&T for durability