Fusion Energy with Lasers and Direct Drive
Total Page:16
File Type:pdf, Size:1020Kb
Laser Direct Drive: Scientific Advances, Technical Achievements, and the Road To Fusion Energy Presented by John Sethian Naval Research Laboratory 1 Fusion Energy with Lasers and Direct Drive Pellet factory Electricity or Hydrogen Spherical pellet Generator Reaction chamber Array of Lasers Final optics 2 Why we believe direct drive with lasers can lead to an attractive power plant 1. Simplest target physics: 2. Laser (most costly component) is modular 3. Separate components lower cost of development 4. Simple spherical targets: facilitates mass produced “fuel" 5. Power plant studies economically attractive 6. We have made a lot of progress!! 3 We are committed to Direct Drive for the Fusion Energy Mission Indirect Drive Direct Drive (Chosen path for NIF) (IFE) Pellet Hohlraum Pellet x-rays Laser Laser Beams Beams • Advanced lasers/ target designs overcome • Relaxed laser uniformity requirements uniformity requirements • Complex targets & physics • Simpler targets & physics • Predict moderate energy gain (≤ 40) • Predict Fusion Class Gains (> 140) at 1 MJ laser energy 4 at lower laser energy (500 kJ - 1 MJ) Two laser options for Direct Drive: KrF and DPPSL Both have potential to meet the IFE requirements Electra KrF Laser (NRL) Mercury DPPSL Laser (LLNL) λ = 248 nm (fundamental) λ = 351 nm (tripled) Gas Laser Solid State Laser See talk by Frank Hegeler See talk by Chris Ebbers Thursday PM Thursday PM 5 6 We encourageAnd competition.leads to it faster It leads to innovation andK a rbetterF product.DPSSL KrF lasers have advantages for fusion energy PHYSICS ● Deeper UV (248 nm vs 351 for glass): -- Greater mass ablation rate and pressure at given intensity -- Higher threshold for deleterious laser plasma instability (LPI) ~1.8x (so maximum ablation pressure is further increased) ● Focus of KrF beams can be readily "zoomed" to follow imploding pellet -- increases coupling by 30% Nike single beam focus ● KrF has most uniform pellet illumination ¾. -- 0.2% non-uniformity overlapped beams ENGINEERING ● Industrial robust technology (used in industry, medical applications) ● Gas laser medium is easy to cool (tough to break gas) 7 Advances and Achievements • target design • lasers • final optics • target fabrication and engagement • chamber 8 New Direct Drive Designs: Power plant class gains, much smaller laser 300 Shock ignition, λ=248 nm Soft Conventional Compression (< 300 km/sec) Then spike to shock heat to ignition Gain for Fusion Energy Conventional Direct Drive 200 (KrF or DPPSL) Enough for energy ~300 km/sec implosion Target …at < 500 kJ Gain 100 FTF Designs, KrF λ= 248 nm Higher ablation pressure 350 to 450 km/sec NIF Indirect Drive 0 00.511.5 22.53 Laser Energy (MJ) 9 Shock Ignition predicts comparable gains as Fast Ignition… without the complexities 300 Shock ignition Fast ignition, λ = 248 nm λ = 248 nm Fast ignition, 200 λ = 351 nm Target Gain 100 Shock ignition proposed by R Betti, University of Rochester 0 00.511.5 22.53 10 Shock Ignition: Shell accelerated to sub-ignition velocity (<300 km/sec), Ignited by converging shock produced by high intensity spike CH Foam/DT (ablator) Foam/DT (ablator)136 μm Ignition Spike s DT Ice (fuel) u DT Ice (fuel) i 300 μm d a r Main DT Vapor m m drive 640 μm 56 7 30 . 21 Laser Intensities Low aspect ratio pellet helps Peak main drive ~ 1.5 × 1015 W/cm2 mitigate hydro instability Igniter pulse is ~1016 W/cm2 11 High resolution 2-D simulations show shock ignition designs are robust against hydro instabilities 2-D Gain: 60× 2-D Gain: 78× 2-D Gain: 69× Outer surface Inner surface Laser Intermediate roughness roughness imprint time Late time Low M Tar fab 250 kJ shock ignited target – NRL FASTRAD3D simulations12 Andy Schmitt NRL Target physics codes have been benchmarked with experiments on Nike Laser Cryogenic Liquid D2 rippled targets Mass variation (mg/cm3) Computer Model time (ns) 13 One challenge, in any laser target design --- Predicting Laser Plasma Instabilities (LPI) X-rays electrons Laser Plasma waves Expanding Plasma DT Fuel Laser driven instabilities cause problems: ¾Produces high energy electrons that preheat DT fuel 14 ¾Scatters laser beam, reducing drive efficiency 2) 16 W/cm Nike experiment to study LaserVUV Plasma spectrometer Instability at prototypical intensities (up to 10 Hard X-ray diodesVUV filtered diodes Target Backlighter beams ra me Ca le ho Pin Collection optics 15 Jim Weaver NRL Targets can be cryogenic –e.g. liquid deuterium Nike Experiments are encouraging: Higher threshold for KrF Onset of LPI ~ 3 x 1015, above target design point Shock target design Spike These experiments:12 Nike backlighter beams 16 will be repeated @ 1 kJ with 44 Nike main beams Jim Weaver NRL brt LLNL (LASNEX) simulations suggest hot electrons induced by spike may be a good thing Gain 60 target may be able to withstand hot electrons up to 100 keV 80 Ehot = 40 keV 60 GAIN 40 Ehot = 100 keV 20 Ehot = 150 keV 0 0 0.2 0.4 0.6 0.8 1.0 Fractional conversion to hot electrons 17 John Perkins LLNL Advances and Achievements • target design • KrF lasers • final optics • target fabrication and engagement • chamber 18 Electra Krypton Fluoride (KrF) Laser - electron beam pumped gas laser Electra KrF Laser 300 -700 Joules 1 Hz to 5 Hz > 7% wall plug efficiency (based on component R&D) 19 see talk by Frank Hegeler (Thurs PM) for details Advanced Solid State Pulsed Power Demo: 1 M shots at 5 Hz, 400,000 shots @ 10 Hz ¾Based on Commercial switches (component life > 300 M shots) ¾ > 80% efficiency ¾Attractive cost: < $ 2 M for Electra (15 kJ) Malcom McGeoch (PLEX) Steve Gldden (APP) see talk by Frank Hegeler (Thurs PM) for details 20 Hibachi foil durability has been a challenge s _wa This__ is a Hibachi Foil .001" thick Stainless Steel Foil Ribs (contain water cooling channels) Typical Foil lifetime: 5,000 - 15,000 shots 21 Plasma Physics to the rescue Spectrometer tuned to look at Ar emission (>700 nm: below Ar, above everything else) Penning Ionization Gauge before after 300 400 500 600 700 800 90022 1000 J Giuliani & R Jaynes (NRL) wavelength (nm) TheThe SmokingSmoking GunGun Penning Ionization Gauge Pinhole Early Notification SW-FL 23 Increasing A-K gap 10%, lowering charge volts 15%: Eliminated voltage reversal, and hence foil emission 300 Red 200 A-K gap 5.3 cm 100 Charge 43 kV Diode 0 Voltage -100 (kV) -200 Blue -300 A-K gap 5.9 cm Charge 36 kV -400 -500 -600 0 200 400 600 800 1200 1600 time (nsec) 24 Electra continuous durability has been extended to the 90,000 shot range Electra Cell after 30,000 shot continuous laser run 90,000 laser shots (10 hrs) continuous @ 2.5 Hz 150,000 laser shots on same foils @ 2.5 Hz 50,000 laser shots on same foils @ 5 Hz 300,000 laser shots in 8 days of operation 500,000 e-beam shots since 12/31/2008 Most runs NOW limited by pulsed power 25 A video starring Electra 26 Advances and Achievements • target design • lasers • final optics • target fabrication and engagement • chamber 27 The final optics train CAD Drawing of Final Optics, Coupled with MCNP simulation of Neutron flux M2 M1 .0003 dpa .02 dpa lifetime lifetime GIMM 1.0 dpa 2 year Mohamed Sawan (Wisconsin) Malcolm McGeoch (PLEX) 28 GIMM laser damage threshold: > 3.5 J/cm2 @ 10 M shots 10 M shots at 3.5 J/cm2 (not a limit!) 29 Mark Tillack (UCSD) Dielectric mirror appears to resist predicted neutron fluence (0.02 dpa) on second mirror The "key": 120 Reflectivity Match neutron-induced swelling (Al2O3/SiO2) in substrate and mirror layers 100 80 Experiment: Expose in HIFR (ORNL Reactor) 60 Prototypical fluence, temperature 40 Measurements: Reflectivity (%) Reflectivity 20 Laser damage threshold 0 200 220 240 260 280 300 Wavelength (nm) Laser Damage Threshold (Al2O3/SiO2) No dpa 0.001 dpa 0.01dpa 0.1 dpa Lance Snead (ORNL) Tom Lehecka (Penn State) 30 86-87% 84-86% 78-83% 83-84% Mohamed Sawan (Wisconsin) Advances and Achievements • target design • lasers • final optics • target fabrication and engagement • chamber 31 Target fabrication: ♦ Mass produce foam shells that meet specs ♦ Fluidized bed for mass cryo layering ♦ Estimate Cost < $0.16 each 100 mg/cc foam shell x-ray picture of 4mm foam Mass Production: 22 shells/min Triple Orifice Generator Variable Speed Pump W2 Cryogenic Fluidized bed DAQ to make smooth DT ice Laser A Input/Output Data PC Laser B Photodiode Sensors Not to scale32 GA, Schaffer, UCSD Recent target fabrication advances: ♦ Higher yield in non-concentricity ♦ Apply thin solid coat on foam during gellation Higher percentage of shells that Proof of concept: meet non concentricity (NC) specs Thin solid coating on Divinyl Benzine foam 100% Spec Advanced DVB foams 60% 75% 1-3% NC RF foams: 10-15% 50% inner surface 25% Early DVB: 0% 0% 0 1 2 3 4 5 6 7 8 5 μm % NC Schaffer Corp 33 General Atomics Additional coating advances made at GA Target Engagement: Concept based on detecting "Glint" off the target. Coincidence sensors Target Glint source Vacuum Align window Focusing Laser Amplifier / mirrors Drive Target multiplexer/ Laser fast steering mirrors Dichroic mirror Cat’s eye retroreflector Target Injector Grazing incidence Wedged mirror dichroic Glint off target mirror 34 Lane Carlson (UCSD) Target Engagement: Bench test: Mirror steers laser beam to target within 34 um. Need ∼20 34 μm RMS error Crossing sensors Glint laser Steering mirror Driver beam Drop tower Poisson spot laser Coincidence sensor Lane Carlson (UCSD) 35 Advances and Achievements • target design • lasers • final optics • target fabrication and engagement • chamber 36 The "first wall" of the reaction chamber must withstand the steady pulses of x-rays, ions and neutrons from the target.