Overview of Inertial Fusion Energy Technology Activities Mark Tillack July 3, 2001 CIEMAT, Madrid 1.Overview of IFE activities in the US 2. Overview of.

Overview of Inertial Fusion Energy Technology ActivitiesMark TillackJuly 3, 2001CIEMAT, Madrid1.Overview of IFE activities in the US2. Overview of IFE activities at UCSD3.Optics damage studies at UCSD

IFE research is coordinated between several distinct program elements

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2500

1200

2000

14000

3000

3000

19000

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Chambers1500

Chamber/Driver interface500

IFE S&E200

S&E (INEEL)277

Target technology800

Chambers1100

Final Optics900

Target technology3000

IFE System Studies (ARIES)1200

HI drivers14000

Laser Drivers19000

Chamber Related (OFES - VLT)2500

ARIES-IFE (OFES - VLT)1200

Target Tech & Design (OFES - Science)2000

Heavy Ion Drivers (OFES - Science)14000

Chamber Related (DP)3000

Target Technology (DP)3000

Laser Drivers (DP)19000

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OFES R&D focuses on two chamber typesHYLIFE-II: Thick-Liquid-Wall ChamberSOMBRERO: Dry-Wall ChamberDifferent scalesFirst wall radius:HYLIFE-II = 3.5 mSOMBRERO = 6.5 mGeorgia Institute of Technology (GT)Idaho National Environmental & Engineering Lab (INEEL)Lawrence Livermore National Laboratory (LLNL)Oak Ridge National Laboratory (ORNL)University of California: Berkeley (UCB), Los Angeles (UCLA), San Diego (UCSD)University of Wisconsin Madison (UW)

IFE chamber research funded by OFESDry-wall chamber researchThick-liquid-wall chamber researchDriver/chamber interfaceheavy-ion driverslaser driversIFE safety and environmental studies

Dry-wall chambers: key features and issuesSOMBREROKey Issue: Chamber Lifetime. Can the first wall be protected from x-ray and debris damage? Can first wall and blanket structures tolerate the effects of neutron damage for an acceptably long time and be designed for economical replacement? Low pressure (< 0.5 Torr), high-Z gas (Xe) protects first wall from short-ranged target emissionsLow activation structures (C/C composites and/or SiC)Flowing Li2O granules serve as breeder and coolantModular blanket for ease of replacementSuited for direct-drive targets

Thick-liquid-wall chambers: key features and issues Thick liquid pocket shields chamber structures from neutron damage and reduces activation

Oscillating jets dynamically clear droplets near target

No blanket replacement required, increases chamber availability

Suited for indirect-drive targetsKey Issue: Chamber Clearing. Can the liquid pocket and beam port protection jets be made repetitively without interfering with beams? Will vapor condensation, droplet clearing and flow recovery occur fast enough to allow pulse rates of ~ 6 Hz?

Driver/chamber interface: heavy ion drivers Key Issue: Self-consistent design. Can superconducting final focusing magnet arrays be designed consistent with chamber and target solid angle limits for the required number of beams, standoff distance to the target, magnet dimensions and neutron shielding thickness? HYLIFE-II with ~ 200 beams

Driver/chamber interface: laser driversKey Issue: Protection and survival. Can final optics be adequately protected from x-rays, debris and dust and survive laser and neutron damage for more than one year before replacement? Will final optics have sufficient mechanical stability under pulsed operation to maintain the required pointing accuracy for target tracking?Two primary options are being considered for the final optic: Grazing incidence metal mirrors Transmissive refractive opticsSi2O or CaF2 wedgesGrazing incidence mirrors

Safety and environmental studiesKey Issues:Power Plants: Can a level of safety be achieved so that a public evacuation plan is not required (< 10 mSv (1 rem) site boundary dose) for credible accident scenarios?Thick-Liquid-Wall Chambers: Can radioactive hohlraum materials be recovered from flibe and recycled in new targets?Dry-Wall Chambers: Can replaced chamber materials be recycled to minimize annual waste volumes? Can tritium retention in candidate materials (C/C composites, SiC) be maintained at an acceptable level?

Goals of the High Average Power Laser ProgramLong term goal:Develop science & technologies required for Inertial Fusion EnergyFocussed on direct drive with lasersBuilds upon recent advances in target design & lasers Complementary technologies (target fab/injection, chambers, final optics)

Short term goal:Science & technologies for a rep-rate laser/target/chamber system for DP needs Study detailed properties of matter relevant to DPRep-rate allows extremely accurate and flexible experimentsComplement high energy single shot facilities

Achieving these goals requires development as a coherent, integrated system

Spin offs:Advanced laser technologiesRobust, high damage threshold opticsAdvanced pulsed power systemsTarget/ chamber/ final optics development for the NIFDevelopment of directed energy technologiesHigh quality science

The elements of the High Average Power Laser Program2. Target FabricationGA: Fab, charac, mass productionLANL: Adv mat, target fab, DT inventory Schafer: Foams, cryo layering6. Chambers Wisconsin: Dry wall, safety, integrate design LLNL: Other walls, target yield, neut damage UCSD: Chamber clearing, materials SNL et al: Materials resp to x-rays & ions1. Direct Drive Target DesignsNRL- Nike ProgramLLNL: Yield spectrum Wisconsin- Yield spectrum3. Target Injection GA: Injector, Injection & TrackingLANL: Materials prop, thermal resp.Targetfactory5. Final OpticsLLNL: X-rays, ions, debris, neut.UCSD: Laser damage, debris mit LANL: Neutrons on optics 4. Lasers NRL: KrF (gas) Laser LLNL: (DPSSL)

The Electra KrF laser (NRL): 1/4 mm, 700 J, 5 Hz

Pump deliveryFront endInjection multi-pass spatial filterDiode pulsersGas-cooled amplifier headThe Mercury dpssl laser (LLNL): 100 J, 1.05 mm, 10 Hz, 2-10 ns, 10% laser for IFE-related experiments

Overview of Inertial Fusion Energy Technology Activities at UC San DiegoMark Tillackhttp://joy.ucsd.edu

July 3, 2001CIEMAT, Madrid

UCSD IFE Technology Program Organization, June 2001

Driver Interface R&D: Beam PropagationProblem Statement The chamber environment following a target explosion contains a hot, turbulent gas which will interact with subsequent laser pulses. Gas breakdown occurs in the vicinity of the target where the beam is focussed. A better understanding of the degree of gas ionization and the effects on beam propagation are needed. The effect of aerosol and particulate in the chamber must be understood in order to establish clearing criteria.

Research Objectives: Determine the laser breakdown threshold in pure and impure chamber environments at low pressure. Determine the effect of chamber environmental conditions on beam propagation.

Beam propagation experiments will be performed in a multi-purpose vacuum chamber under constructionInitial measurements: Visible light emission from the focal spot Variation in laser energy profile (CCD) & temporal pulse shape (photodiodes) Wavefront variation (Shack-Hartmann)

Planned future measurements: Emission spectroscopy Changes in spatial profile with 2% accuracyKey Program Elements Construction of a multi-purpose vacuum chamber Breakdown emission detection and spectroscopy Laser beam smoothing and accurate profiling (goal of 2-5%)

Chamber Physics Modeling and ExperimentsProblem StatementThe chamber condition following a target explosion in a realistic chamber geometry is not well understood. The key uncertainty is whether or not the chamber environment will return to a sufficiently quiescent and clean low-pressure state to allow another shot to be initiated within 100200 ms. Modeling and experimental capabilities are needed to predict the behaviour of an IFE power plant chamber and to ensure that all relevant phenomena are taken into account. Objectives Develop and benchmark an integrated, state-of-the-art computational model of the dynamic response of IFE chambers following target explosions Use the code to plan experiments and study IFE chambers Demonstrate validity of scaling and simulation experiments Develop chamber experimental capabilities Provide new data relevant to IFE chamber responses

Multi-physics model of chamber dynamics

Chamber Physics Simulation ExperimentsHYADES simulation of laser irradiation of AuEnergy required to simulate IFE chamber issues

1-10 J

Optics damage

Beam propagation

Surface physics and near-surface chamber interactions

Diagnostic development and experimental techniques

100-500 J

Volumetric tests in small prototypical chambers (~1 liter)

1-10 kJ

Simultaneous surface and volume effects (~10 liter)

>10 MJ

Integrated prototypical chamber testing

Engineering Modeling of IFE TargetsInput ParametersInitial target configurationProperties databaseImposed accelerationsThermal environmentChamber gas, aerosol and particulate speciesChamber hydrodynamic environmentComputed ParametersTarget temperature distributionTarget trajectoryTarget internal stress distributionInternal mass transportIn-hohlraum beta layering analysis:

IFE Wall EngineeringRHEPP/MAP ion beam facility, SNLA ESLI carbon fiber flocked surface Structured surfaces may offer superior thermal response and improved erosion behavior under exposure to pulsed energy sources

Studies of Laser Induced Damageto Grazing Incidence Metal Mirrors Mark Tillackhttp://joy.ucsd.edu

July 3, 2001CIEMAT, Madrid

Geometry of the Driver-Chamber InterfacePrometheus-L reactor building layout(30 m)(SOMBRERO values in red)(20 m)Grazing incidence mirrorsSi2O or CaF2 wedges

GIMM development issues** from Bieri and Guinan, Fusion Tech. 19 (May 1991) 673. Experimental verification of laser damage thresholds

Wavefront issues:beam smoothness, uniformity, shaping,f/number constraints

Experiments with irradiated mirrors

Protection against debris and x-rays (shutters, gas jets, etc.)

In-situ cleaning techniques

Large-scale manufacturing

Cooling

Aluminum is the 1st choice for the GIMMNormal incidence reflectivity of metals Lifetime of multi-layer dielectric mirrors is questionable due to rapid degradation by neutrons

Al maintains good reflectivity into the UV

Al is a commonly used mirror material easy to machine, easy to deposit

Thin (~10 nm), protective, transparent oxide

Normal incidence damage threshold ~0.2 J/cm2 Grazing incidence raises s-reflectivity to >99% Larger footprint reduces fluence by cos(q) Combined effects hopefully raise the damage threshold to >5 J/cm2

Several surface types have been fabricateddiamond-turned Al 6061MgSi occlusions99.999% pure AlAl 110075 nm Al on superpolished flat: 2 roughness, 10 flatness

UCSD Laser Plasma and Laser-Material Interactions LaboratoryQ ~ 200 mradSpectra Physics laser:2J, 10 ns @1064 nm700, 500, 300 mJ @532, 355, 266 nmPeak power~1014 W/cm2ProfilingShack-Hartmann

Ringdown reflectometry is used for accurate measurements and in-situ surface monitoring100 ppm accuracy

In-situ reflectometry can measure surface changes not visible to the naked eye

1000 shots in Aal 1100 at 85, 1 J/cm2 peak Al 1100 shows no apparent damage up to 1 J/cm2Several shots in Al 6061 at 80, 1 J/cm2 peak FeFe MgSi 1000x Damage occurs at a higher fluence as compared with normal incidenceSilicide occlusions in Al 6061 preferentially absorb light, causingexplosive ejection and meltingFe impurities appear unaffectedExposure of Al 1100 to 1000 shots at 85 exhibited no damage1000x

Tools for modeling effects of damage on beam characteristics

Dimensional Defects

Compositional Defects

Gross deformations, >

Surface morphology,

Effect of Surface Coatings and ContaminantsCarbon film thickness (nm)reflectivityq1 = 0o20o40o60o80olo = 532 nmAl2O3 coating (10 nm)Al mirrord2=2 nmq1 = 0od2=2 nmq1 = 80od2=0q1 = 0od2=0q1 = 80olo = 532 nmCarbon film Al mirrorreflectivityAl2O3 coating thickness, d3/lo 4-layer Fresnel model was developed to examine behavior of coatings and contamination Surface contaminants (such as carbon) on mirror protective coatings can substantially alter reflectivity, depending on layer thickness and incident angle.

The effect of induced surface roughness on beam quality was investigated using Kirchhoff wave scattering theorye.g., at q1 = 80o, s/l = 0.1, e-g = 0.97Specularly reflected intensity is degraded by induced mirror surface roughness For cumulative laser-induced and thermomechanical damages, we assume Gaussian surface height statistics with rms height s. 0 0.1 0.2 0.3 0.4 0.51.0

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0q1 = 80o70o60oIntensity Degradation, egs / lGrazing incidence is less affected by surface roughness To avoid loss of laser beam intensity, s / l < 0.01Io : reflected intensity from smooth surfaceId : scattered incoherent intensityg : (4p s cosq1/l)2Iinc

Graduate Studies in Plasma Physics & Controlled Fusion ResearchCurrent Research Areas:

Theoretical low temperature plasma physics Experimental plasma turbulence and transport studies Theoretical edge plasma physics in fusion devices Plasma-surface interactions Diagnostic development Semiconductor manufacturing technology Theory of emerging magnetic fusion concepts Fusion power plant design and technology Radio-frequency heating and current drive Laser-matter interactions and inertial confinement fusion Thermo-mechanical design of nuclear fusion reactor components Theoretical space and astrophysical applicationsInterested students are encouraged to visit our website at: http://www-ferp.ucsd.edu/brochure.htmlfor information on our research, available financial support and university admissions policy.University of California, San DiegoSchool of Engineering