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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

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Phase II Considerations: Diode Pumped Solid State Laser (DPSSL) Driver for Inertial Fusion Energy

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  1. 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

  2. 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

  3. 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

  4. Solid state laser driver requirements for Inertial Confinement Fusion NIF / IFE are same Enhancements needed

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

  6. Efficiency comparison NIF and Mercury-like architectures (estimates) Convection Nd:glass Radiative Radiative Frequency cooling cooling conversion Reflector Yb Yb :S :S - - FAP FAP Turbulent cooling Frequency conversion Mercury Higher efficiency of DPSSL is achieved through many enhancements

  7. Ripple growth Laser slab ASE losses Gain medium deployed in solid state laser has fundamental consequences on cost and performance Energy Levels Storage time determines diode cost Gain Saturation fluence is FSAT = hn / sG 2 MJ laser and 5¢/W diodes Cdiode ($B) = 0.5 / tST (ms) Peak fluence: FPEAK = 4.5 FSAT Bandwidth for smoothing: DnG Beam Energy Balances amplified spontaneous emssion (ASE) and nonlinear ripple growth Saturation fluence laser pulse width Ebeam = (hEXT / 12 FSAT) (3 ltP / 4g)2 extraction efficiency nonlinear index

  8. 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 Longer lifetime reduces cost Lower fluence reduces damage Beam energies are similar Bandwidth is adequate • Yb:S-FAP has 2.5x greater thermal conductivity than Nd:glass •  better for rep-rated operation • However, crystals are more difficult to produce in large size

  9. 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

  10. Quadrant of desired operation 10 x 15 cm2 1.7 kJ 20 x 30 cm2 Design point Optical-Optical Efficiency 4.2 kJ 30 x 45 cm2 8.3 kJ B-Integral, radians (beam modulation) Ripple growth Laser slab ASE losses S&T issue #1: Models indicate that multi-kilojoule output is feasible from a single coherent aperture • 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 3w-conversion of ~75% to be included • Reduced losses and higher diode efficiency possible

  11. Widely-spaced architecture Fitting function: Peak-to-Ave = Static · (1 + Alpha · eB) 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 slabs have more intensity on pinhole 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

  12. SRS Laser S&T issue #3: Stimulated Raman Scattering (SRS) in S-FAP, or unwanted nonlinear frequency conversion, must be controlled in the IRE Gain lowers with angle between laser and SRS SRS is predicted for the IRE based on gain Tm:YAG absorber suppresses SRS Quantitative modeling yields: - Aperture limit is >20x30 cm2 at 3 GW/cm2 - Longitudinal SRS is controlled by: - inserting Tm:YAG absorber in amps - adding a small wedge to the slabs

  13. S&T issue #4: Combination of bonding and large diameter growth provides pathway to 20x30 cm2 Yb:S-FAP slabs 3.5 cm boules (standard) 6.5 cm boules (last year) 10 cm boules needed for IRE Bonding choices Schott - “glue” bonding Onyx - high temperature Approximately 10 cm boules will be needed to bond three parts together for each 20x30 cm2 slab

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

  15. He cooling He cooling 3w 1w 2w BBO doubler BBO tripler 2.5 mm 4 mm Conversion vs. Intensity (thermally loaded) Conversion vs. detuning @ 0.7 GW/cm2 KDP, YCOB BBO S&T issue #6: Average power frequency conversion with >80% efficiency can be obtained for ~ 1 THz bandwidth using BBO crystal • Main challenge is to “tile” multiple BBO crystals to cover aperture of beam • - Based on current technology, four crystals must be tiled for Mercury

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

  17. Phase I resolves most issues associated with component design and functionality • 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 • 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)

  18. Cost Breakdown for Phase II: DPPSL 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 Timeline for DPSSL- IRE (6 kJ) development and operation (rough estimate) Laser Design $12M Construct & Procure $135M Laser Activation $22M Integrated experiments Laser:$36M; Chamber:$10M Vendor readiness $22M Chamber Design $0.5M Construct & Procure $6M Chamber Activation $9.5M Vendor Readiness ($22M): - Contracts ($10), Crystal growth ($6.5), Overhead ($5.3) Design ($12M): - Personnel ($7.2), Overhead ($4.8) Procurement and Construction ($135M): - 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 ($22M): - Personnel ($8.1), Crystals ($4.8), Procurements ($1.2), Overhead ($7.6) Integrated experiments ($36M): - Personnel ($12.0), Crystals ($3.6), Procurements ($1.8), Overhead ($18.6) $277M Personnel and Laser Hardware ($168M + $50M contingency) - LLNL Overhead ($59M; Assumes 30% reduction in tax base)

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

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