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Phase II Considerations: Diode Pumped Solid State Laser (DPSSL) Driver for Inertial Fusion Energy Phase II Considerations: Diode Pumped Solid State Laser (DPSSL) Driver for Inertial Fusion Energy Steve Payne, Camille Bibeau, Ray Beach, and Andy Bayramian National Ignition Facility Directorate Lawrence Livermore National Laboratory Livermore, California 94550 HAPL Review February 6, 2004 Atlanta, GA

Outline • Comparison of DPSSL with NIF - Requirements - Technologies • Critical Phase Outline • Comparison of DPSSL with NIF - Requirements - Technologies • Critical Phase II science and technology issues - Beam energy - Nonlinear beam propagation - Stimulated Raman scattering - Crystal growth - Diode cost - Frequency conversion - Beam bundling • ROM cost and schedule

Fusion laser architectures are predicated on meeting target physics and power plant system-level requirements Fusion laser architectures are predicated on meeting target physics and power plant system-level requirements Target Gain • Energy • Pulse shape • Smoothness • Wavelength IFE Power Plant • Efficiency • Reliability • Diode cost • Repetition rate • Target requirements similar to NIF • Additional system-level requirements imposed on IFE lasers

Solid state laser driver requirements for Inertial Confinement Fusion Gain Medium NIF / IFE Solid state laser driver requirements for Inertial Confinement Fusion Gain Medium NIF / IFE are same Energy NIF (stockpile stewardship) IFE (energy) Integrated Research Exp. (scaling) Mercury (prototype) 2 MJ 192 beams x 10 k. J 2 MJ 700 beams x 3 k. J 6 k. J 2 beams x 3 k. J 100 J 1/30 aperture 3 ns at <0. 4 mm Pulse shape, wavelength Smoothness Efficiency Enhancements needed s<3% in 1 nsec s < 0. 1 % in 1 ns (beams overlapped) 0. 8%, no utilities Cost $1000/J; Flash lamps used Rep-rate 10 -4 Hz Reliability 104 shots 5 - 10%, wall-plug $500/J - laser; $0. 05/W - diodes s < 10 % in 1 nsec 5 - 10%, no utilities $40 k/J - laser; $1/W - diodes $400 k/J - laser; $5/W - diodes 10 Hz • 1010 for diodes • 108 for optics • 109 - diodes • 107 - optics • 108 - diodes • 106 - optics

Comparison of NIF and Mercury amplifiers Mirror Our new architectural layout of optics and Comparison of NIF and Mercury amplifiers Mirror Our new architectural layout of optics and amplifiers Telescope • Collinear diode pumping and beam path extraction - improves gain uniformity and pump efficiency - integrates spatial filter and pump cavity Amplifiers • Closely-spaced slabs and lenses in compact amplifier cavity - reduces “B-integral” or beam intensity modulations Flashlamps - optics located where damage probability is lowest Reflectors Diodes Gas cooled

Efficiency comparison NIF and Mercury-like architectures (estimates) Mercury Frequency conversion 95 50 45 70 Efficiency comparison NIF and Mercury-like architectures (estimates) Mercury Frequency conversion 95 50 45 70 60 85 95 Absorption 40 90 90 Quant Def 60 86 86 67 80 80 67 N/A 67 60 65 70 Fill Turbulent cooling 85 Extraction Yb: S-FAP 82 ASE Reflector IFE Emission Frequency conversion Hg Xport Nd: glass NIF Pump Radiative cooling Eff. (%) Power Convection 85 85 92 Xport 93 N/A 95 Freq Conv 60 75 75 Total (%) 0. 75 8. 3 12. 0 Higher efficiency of DPSSL is achieved through many enhancements

Gain medium deployed in solid state laser has fundamental consequences on cost and performance Gain medium deployed in solid state laser has fundamental consequences on cost and performance Gain Energy Levels Storage time determines diode cost Saturation fluence is FSAT = hn / s. G 2 MJ laser and 5¢/W diodes Cdiode ($B) = 0. 5 / t. ST (ms) Peak fluence: FPEAK = 4. 5 FSAT Bandwidth for smoothing: Dn. G Beam Energy Balances amplified spontaneous emssion (ASE) and nonlinear ripple growth Laser slab Ripple growth Saturation fluence laser pulse width Ebeam = (h. EXT / 12 FSAT) (3 l t. P / 4 g)2 ASE losses extraction efficiency nonlinear index

Yb: S-FAP laser material offers advantages over Nd: glass for IFE Comparison of Nd: Yb: S-FAP laser material offers advantages over Nd: glass for IFE Comparison of Nd: glass and Yb: S-FAP gain media in fusion lasers Gain Medium Diode Cost 0. 5 / tst Damage 4. 5 Fsat NIF (Nd: glass) $1. 25 B (hypothetically diode-pumped) 24 J/cm 2 IFE (Yb: S-FAP) $0. 45 B 14 J/cm 2 4. 4 k. J 0. 3 THz 1. 0 THz @ 3 w Lower fluence reduces damage Beam energies are similar Bandwidth is adequate Longer lifetime reduces cost Beam Energy, Ebeam (3 nsec pulse) 5. 6 k. J (10 k. J with higher ASE losses) 1 w Band Width, Dn 1 THz • Yb: S-FAP has 2. 5 x greater thermal conductivity than Nd: glass better for rep-rated operation • However, crystals are more difficult to produce in large size

Outline • Comparison of DPSSL with NIF - Requirements - Technologies • Critical science Outline • Comparison of DPSSL with NIF - Requirements - Technologies • Critical science and technology issues - #1 - Beam energy / amplified spontaneous emission - #2 - Nonlinear beam propagation / optical damage - #3 - Stimulated Raman scattering - #4 - Crystal growth - #5 - Diode cost - #6 - Frequency conversion - #7 - Beam bundling • ROM cost and schedule

Laser slab ASE losses Ripple growth Optical-Optical Efficiency S&T issue #1: Models indicate that Laser slab ASE losses Ripple growth Optical-Optical Efficiency S&T issue #1: Models indicate that multi-kilojoule output is feasible from a single coherent aperture Quadrant of desired operation 10 x 15 cm 2 1. 7 k. J Design point 20 x 30 cm 2 4. 2 k. J 8. 3 k. J 30 x 45 cm 2 B-Integral, radians (beam modulation) • Amplified spontaneous emission rates are accelerated for larger slabs • Greater extraction efficiency leads to higher B-integral (i. e. beam modulation) • Diode efficiency of ~60% and 3 w-conversion of ~75% to be included • Reduced losses and higher diode efficiency possible

S&T issue #2: Mercury “closely-spaced slab” architecture has reduced nonlinear beam breakup relative to S&T issue #2: Mercury “closely-spaced slab” architecture has reduced nonlinear beam breakup relative to “widely-spaced” (NIF-like) architecture Focal spots Widely-spaced architecture Widely-spaced slabs have more intensity on pinhole Fitting function: Peak-to-Ave = Static · (1 + Alpha · e. B) B = 3. 8 radians Mercury: Closely-spaced slabs B = 3. 8 radians Optical damage risk is mitigated in Mercury architecture two ways: • Closely-spaced-slab architecture reduces nonlinear ripple growth • Lower saturation fluence of Yb: S-FAP vs. Nd: glass reduces average fluence

S&T issue #3: Stimulated Raman Scattering (SRS) in S-FAP, or unwanted nonlinear frequency conversion, S&T issue #3: Stimulated Raman Scattering (SRS) in S-FAP, or unwanted nonlinear frequency conversion, must be controlled in the IRE SRS is predicted for the IRE based on gain Gain lowers with angle between laser and SRS Tm: YAG absorber suppresses SRS Quantitative modeling yields: SRS Laser - Aperture limit is >20 x 30 cm 2 at 3 GW/cm 2 - Longitudinal SRS is controlled by: - inserting Tm: YAG absorber in amps - adding a small wedge to the slabs

S&T issue #4: Combination of bonding and large diameter growth provides pathway to 20 S&T issue #4: Combination of bonding and large diameter growth provides pathway to 20 x 30 cm 2 Yb: S-FAP slabs 3. 5 cm boules (standard) 6. 5 cm boules (last year) 10 cm boules needed for IRE Onyx - high temperature Bonding choices Schott - “glue” bonding Approximately 10 cm boules will be needed to bond three parts together for each 20 x 30 cm 2 slab

S&T issue #5: Learning curve analysis suggests that diode bar prices will drop as S&T issue #5: Learning curve analysis suggests that diode bar prices will drop as the market grows Low duty cycle diode bars Diode packaging house created from LLNL tech-transfer - High production rate reduced cost - Higher efficiency diodes are desired Diode laser bars Heatsinks Backplanes

S&T issue #6: Average power frequency conversion with >80% efficiency can be obtained for S&T issue #6: Average power frequency conversion with >80% efficiency can be obtained for ~ 1 THz bandwidth using BBO crystal He cooling 3 w 1 w 2 w BBO doubler 2. 5 mm Conversion vs. Intensity (thermally loaded) BBO tripler 4 mm Conversion vs. detuning @ 0. 7 GW/cm 2 KDP, YCOB BBO • Main challenge is to “tile” multiple BBO crystals to cover aperture of beam - Based on current technology, four crystals must be tiled for Mercury

S&T issue #7: Amplifier can be integrated into bundles and clusters to simplify cooling S&T issue #7: Amplifier can be integrated into bundles and clusters to simplify cooling and minimize the footprint 4 k. J beam lines Clusters of bundles 36 k. J bundle of 12 apertures Management of high average power likely to be very challenging

Phase I resolves most issues associated with component design and functionality Phase I resolves: Phase I resolves most issues associated with component design and functionality Phase I resolves: • Yb: S-FAP performance • Laser architecture and gas-cooling • Pockels cell design • Optical damage • Diode package • Diode commercialization • Laser operations • Beam smoothing • Control system architecture • Nonlinear beam propagation (#2) • Frequency conversion (#6) Phase II resolves: • Beam energy (#1) • Stimulated Raman scattering (#3) • Scale-up of crystals & bonding (#4) • Mass production of diodes (#5) • Beam bundling (#7) • Higher diode eff. , 45 60% • Management of higher power

Timeline for DPSSL- IRE (6 k. J) development and operation (rough estimate) Cost Breakdown Timeline for DPSSL- IRE (6 k. J) development and operation (rough estimate) Cost Breakdown for Phase II: DPPSL 2006 2007 Laser Design $12 M 2008 2009 2010 Construct & Procure $135 M 2011 2012 Construct & Procure $6 M 2014 Integrated experiments Laser: $36 M; Chamber: $10 M Chamber Activation $9. 5 M Vendor Readiness ($22 M): - Contracts ($10), Crystal growth ($6. 5), Overhead ($5. 3) Design ($12 M): - Personnel ($7. 2), Overhead ($4. 8) Procurement and Construction ($135 M): - Personnel ($10) - Diodes (assumed cost $1. 2 / Watt, 30 MW) ($39. 6) - Crystals ($10) - Laser Hardware ($12. 9) - Power Conditioning ($17) - Facilities and Utilities ($22. 9) - Overhead ($22. 3) Activation ($22 M): - Personnel ($8. 1), Crystals ($4. 8), Procurements ($1. 2), Overhead ($7. 6) Integrated experiments ($36 M): - Personnel ($12. 0), Crystals ($3. 6), Procurements ($1. 8), Overhead ($18. 6) $277 M 2015 Laser Activation $22 M Vendor readiness $22 M Chamber Design $0. 5 M 2013 Personnel and Laser Hardware ($168 M + $50 M contingency) - LLNL Overhead ($59 M; Assumes 30% reduction in tax base)

Rep-rated high-energy solid-state laser initiatives have sprung up around the world, which is likely Rep-rated high-energy solid-state laser initiatives have sprung up around the world, which is likely to accelerate progress