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A Summary Report on the 21st Century Needs and Challenges of

Compression Science Workshop

Bishop’s Lodge, Santa Fe, NM

September 22-25, 2009

Organizers:

Dave Funk, Rusty Gray, Tim Germann, and Rick Martineau Image by NASA/JPL-CalTech

LA-UR 09-07771

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TableofContents

1. Introduction ............................................................................................................................................................ 5

2. Breakout Summaries.............................................................................................................................................. 72.1 Static Compression Science............................................................................................................................... 72.2 Scientific Discovery Challenges: Static Compression Science ......................................................................... 7

2.2.1 Structure and bonding at high compression............................................................................................... 72.2.2 New physics in cold dense matter ............................................................................................................. 82.2.3 Fundamental thermodynamics................................................................................................................... 82.2.4 Time-dependent transformations ............................................................................................................... 92.2.5 High-pressure strength, plasticity, and rheology ....................................................................................... 92.2.6 Synthetic chemistry frontier .................................................................................................................... 102.2.7 Optimized new materials ......................................................................................................................... 112.2.8 Radiation-induced high-pressure chemistry ............................................................................................ 112.2.9 Earth science, planetary science and astrophysics................................................................................... 122.2.10 Life in extreme environments ................................................................................................................ 12

2.2 Technical Grand Challenges in ‘Static’ Compression Science....................................................................... 132.2.1 Reaching 1 TPa and beyond .................................................................................................................... 132.2.2 Developing multi-probe ‘intelligent’ devices .......................................................................................... 132.2.3 Stress-strain states and P-T calibration.................................................................................................... 132.2.4 Advancing x-ray methods........................................................................................................................ 142.2.5 Real time x-ray imaging with nm resolution ........................................................................................... 142.2.6 Neutron scattering to multi-megabar pressures ....................................................................................... 142.2.7 Challenge of liquids and amorphous materials........................................................................................ 152.2.8 Filling the strain rate gap: Static to shock ............................................................................................... 152.2.9 Transport properties................................................................................................................................. 162.2.10 Thermochemical measurements at multimegabar pressures ................................................................. 16

3. Dynamic Compression Science ........................................................................................................................... 173.1 Scientific Discovery Challenges: Dynamic Compression Science .................................................................. 17

3.1.1 Kinetics and mechanisms of melting, freezing, and solid-solid phase transformations .......................... 173.1.2 Warm dense matter (WDM): metallization, release around critical points ............................................. 183.1.3 Evolution of microstructure under dynamic loading including defect distributions ............................... 183.1.4 Experiment/theory convergence: Developing the ability to reproduce simulations of ‘real systems’ for better understanding of experimental observations. ............................................................................................. 193.1.5 Resolving the details of detonation and shock-induced chemistry.......................................................... 203.1.6 Discovering new phases and forms of matter at ultra-high compression using tunable pathways and controlling reaction chemistry through pressure and temperature ....................................................................... 203.1.7 Discovering and understanding of the partitioning between dissipative and non-dissipative mechanisms 213.1.8 Determine the role of shear in deformation processes............................................................................. 213.1.9 Develop understanding of the role of interfacial boundaries................................................................... 213.1.10 Develop an understanding of the transition in material plasticity and damage evolution across the ‘thermally activated’ to ‘shock’ to ’drag control’ regimes................................................................................... 21

3.2 Technical Grand Challenges in ‘Dynamic’ Compression Science ................................................................. 223.2.1 Characterization of melting, freezing, and solid-solid phase transformations ........................................ 223.2.2 Real-time diagnostics for dynamic mapping of the thermo-mechanical field......................................... 223.2.3 Ability to make experimental measurements to link length scales ranging from atomic to continuum dimensions ............................................................................................................................................................ 233.2.4 Ability to make in situ spectroscopic measurements including those of electronic structure ................. 233.2.5 Complex loading path control ................................................................................................................. 233.2.6 Develop first-order continuum analyses that produce better subscale models and capture defect evolution ............................................................................................................................................................... 24

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3.2.7 Learn how to conduct and diagnose experiments relevant to 3D applications........................................ 243.2.8 Design experiments that overlap different loading regimes and experimental platforms ....................... 243.2.9 Increase experimental throughput............................................................................................................ 243.2.10 Develop improved materials and standards for uniform comparisons .................................................. 24

3.4 Scientific Discovery Challenges for Compression Science Theory and Modeling ......................................... 263.4.1 Track dynamic microstructure evolution in situ ...................................................................................... 263.4.2 Discover new and unexpected high-pressure and temperature solid phases ........................................... 263.4.3 Design novel experiments to isolate key physics .................................................................................... 273.4.4 Move beyond planar impact: Non-uniaxial strain experiments............................................................... 273.4.5 Design novel simulations to isolate key physical mechanisms and observables..................................... 273.4.6 Develop ability to predict the kinetics of phase transitions (solid-solid, solid-liquid, and liquid-solid). 283.4.7 Understand relationship between microstructure and constitutive properties (e.g., strength) during dynamic processes ................................................................................................................................................ 283.4.8 Understand material failure ..................................................................................................................... 283.4.9 Resolve melting discrepancy in transition metals ................................................................................... 293.4.10 Understand the behavior of the full anisotropic stress state at extreme pressures and temperatures, e.g., Poisson’s ratio approaching melt.......................................................................................................................... 29

3.5 Technical Grand Challenges for Compression Science Theory and Modeling .............................................. 293.5.1 Multiscale modeling free of ad hoc parameters: linking subscale processes to higher length/time scales 293.5.2 Better theoretical tools in the mesoscale (1–10 mm) regime .................................................................. 303.5.3 Transferable density functionals, pseudopotentials, and classical MD potentials valid at extreme conditions ............................................................................................................................................................. 303.5.4 Equation of state treatment of materials beyond simply pressure and volume ....................................... 313.5.5 Codes that preserve the integrity of material models .............................................................................. 313.5.6 Quantitative dynamic x-ray probes (diffraction, XANES, EXAFS, etc.) ............................................... 313.5.7 Develop local temperature and stress tensor gauges ............................................................................... 323.5.8 Local structural identification in static experiments, e.g., DAC, for amorphous materials and liquids.. 323.5.9 3D orientation image mapping to dislocation length scales under dynamic conditions.......................... 323.5.10 Extracting useful information from high-resolution 3D data (e.g., from 3D tomography or large-scale simulations) .......................................................................................................................................................... 33

4.0 Conclusions ......................................................................................................................................................... 34

Appendix I Workshop Agenda................................................................................................................................ 35

Appendix II Participants ......................................................................................................................................... 38

Appendix III Cross-cutting issues identified during the workshop..................................................................... 41

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ExecutiveSummary

Theinfluencethatcompressionsciencehashadonnationalsecurityscienceanditsmanifestationthroughdiscoveryandapplicationcannotbeoverstated.Inadditiontosupportingthecertificationofournuclearstockpileintheabsenceofundergroundtestingandabroadspectrumofengineeringanddefenseapplications,compressionsciencehasalteredourviewofthematerialworldaroundus.Thediscoveryofunexpectedphysicalandchemicalphenomenaandnewmaterialsthroughtheapplicationofcompressionsciencetechniqueshasledtoanewandrefinedunderstandingofthenatureofchemicalbondinginextremeenvironments.However,itisclearthatmanyimportantaspectsregardingtheresponseofmaterialstocompressiveloadingarestillnotunderstood,letalonemodeledinapredictivemode.Asaresult,wehavenotderivedthemanybenefitsthatapredictiveunderstandingwouldbring.Asoneproductoftheworkshopweheld,weidentifiedfivechallengesthatcapturethescientificneedsthatarerequiredtoachievefullunderstandingandthatultimatelysupportourultimategoalofmovingfrom“observationtocontrol.”

Thesefivechallengesareasfollows:

• Acquiretimeandspatiallyresolvedinsitumeasurementsatalllengthscales(i.e.,atomistic,micro‐,meso‐).

• Discovernewphysicsandchemistryinextremeenvironments.• Incorporatematerialcomplexityintomulti‐scalesimulationstoachievepredictive

capability.• Unifystaticanddynamiccompressionunderstandingacrossrelevantlengthandtime

scales.• Leveragescientificknowledgederivedfromtheoryandexperimenttothedesignand

controlofrealmaterials(i.e.,chemistry,microstructure,defects,etc.)

Makingprogressonthesechallengeswillrequireasuiteofnewexperimentaltoolsanddiagnosticsaswellasasuiteofconceptualframeworksandtheoreticalconstructs.Thesuiteofexperimentaltoolsmustincludethedevelopmentofdiagnosticcapabilities,suchasnextgenerationlightsources,forpeeringintoandachievingtime‐resolvedmeasurementsincompressedmaterialsatthelowestrelativelengthscaleswhilesimultaneouslycharacterizingthemathigherlengthscales.Thetheoreticalsuitemustincludenewframeworksofcomputationthatwillallowtheincorporationofthestochasticnatureofmatter,aswellastheabilitytoaccuratelydescribetheessentialphysicswithouttheinvocationofphenomenologicalmodels,whilelinkingtheatomistictothecontinuumresponse.

Progressonthesechallengeswillnotonlyallowustodevelopafullunderstandingofcompressionscience,itwillcreateanenvironmentinwhichwecantrainthenextgenerationofscientistsandprovidethemwiththetoolsneededtomakeprogressandmovefromstudying“Ideal”to“Real”materials.

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1. Introduction Forapplicationsinthefuture,thedesign,synthesis,andmanufactureofnewmaterialswithincreasedperformanceandfunctionalityrequireanincreaseinourfundamentalunderstandingofmatteroverthebroadestrangeofthermomechanicalconditions.Furthermore,accesstoextremestatesofmatterresultsinaricharrayofphysicalandchemicalchangesthatrequiresabroadrangeofscience—fromquantumphysicstothecollectivecontinuumresponse—tointerpret.Infact,currentresearchreiteratesthisneed:“Compressioninduceschangesinbondingproperties,givingrisetoaltogethernewcompoundsandcausingotherwiseinertatomsormoleculestocombine.Whencoupledwithchangesintemperature,altogethernewformsofmattermaybeproduced.Forexample,ithasrecentlybecomepossibletouselaboratorytechniquestocompressmaterialstothepointwheretheinteratomicspacingsarereducedbyuptoafactoroftwoanddensitiesincreasedbyoveranorderofmagnitude.Atthesedensities,thechangesintheelectronicstructurebegintoinfluenceourverynotionsofchemicalinteractionandatomicbonding.”1

Thus,fullyexploitingthepossibilitiesofchemicalbonding,asderivedfromtheapplicationofpressureandtunedwithtemperature,willrequirenewtoolstogeneratetheseextremeenvironments,butwillalsorequireanabilitytodiagnoseand“calculate”them.Thefieldofcompressionsciencehasgeneratedrichinsightandmadeusawareofthefactthatwedonotfully understand the nature of the processes that we induce with pressure. Presently,pressures reachedduring static compressioncanexceed the300GPa (3Mbar) rangeandcantemporarilyexceedtemperaturesgreaterthanthatofthesurfaceofoursun(>6,000K),whilethosepressuresreachedduringdynamiccompressioncanexceedtheTeraPascal(TPaor10Mbar)range.Inaddition,thedynamicprocessesofshockcompressionaresofastthatthe loading is usually adiabatic, the typical durations range from femtosecond tomicrosecondtimescales,andtemperaturesreachgreaterthan104K,dependingontherateof loading and the magnitude of the peak compression. Developing new capabilities forreaching further extremes and diagnosing these equilibrium states of matter withunprecedented spatial resolutionwill informand advance our understanding, assisting inourgoalofmovingfrom“observationscience”to“controlscience.”Toquantifytheseneedsandfuturedirections,leadersinthestatic,dynamic,andtheoryofcompression sciences participated in a workshop entitled, “21st Century Needs andChallengesinCompressionScience,”heldSeptember22‐25,2009,inSantaFe,NewMexico.A series of plenary talks were given (see Appendix I), followed by a day of breakoutdiscussionsintheareasofstaticcompressionscienceneeds,dynamiccompressionscienceneeds, and theoretical needs of compression science to define the decadal technicalchallengesandnecessarydevelopmentstomeetthesechallenges

1 “Basic Research Needs for Materials Under Extreme Environments,” a report of the Basic Energy Sciences Workshop on Materials Under Extreme Environments, June 11-13, 2007, Jeff Wadsworth, Chair, George Crabtree and Russel Hemley, co-Chairs.

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Atitshighestlevel,theneedsofcompressionsciencecouldbecapturedbythefollowingfivechallenges:

•Acquiretimeandspatiallyresolvedinsitumeasurementsatalllengthscales(i.e.,atomistic,meso‐,micro‐).

•Discovernewphysicsandchemistryinextremeenvironments.•Incorporatematerialcomplexityintomulti‐scalesimulationstoachievepredictive

capability.•Unifystaticanddynamiccompressionunderstandingacrossrelevantlengthandtime

scales.•Leveragescientificknowledgederivedfromtheoryandexperimenttothedesignand

controlofrealmaterials(i.e.,chemistry,microstructure,defects,etc.).

The ability to address these challenges will require a new set of characterization tools,temporally and spatially enhanced diagnostics, and the development of new predictivemodels to characterize the behavior of matter under these extreme conditions. Theinformation gathered in static compression science experiments, when combined withinformationacquireddynamically,offerstheopportunityofunderstandingthefundamentalmechanisms that drive the processes occurring in the matter observed throughout theuniverse, ultimately leading to an ability of controlling matter to meet our energy andnationalsecurityneeds.

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2. Breakout Summaries

2.1 Static Compression Science Staticcompressionscienceisaburgeoningfieldthatisundergoingunprecedentedgrowthinaddressingabroadrangeofmaterialsproblemsthatspanthephysical,engineering,andbiologicalsciences.Methodsthatrelyonstaticcompressionexperimentshavemanyadvantages,includingtheavailabilityofmultiplesimultaneousdiagnostics.Thesediagnosticshavethepotentialforfullmaterialscharacterizationwithanaccuracy,precision,andsensitivitythatapproachesmeasurementsonmaterialsatnearambientconditions.Thefieldisturningitsattentiontoaddressingmajorgrandchallengesinmaterialsscience,includingtheDOEGrandChallengesofmovingfromobservationtocontrolscienceandharnessingmaterialsfarfromequilibrium.Thereisastrongsynergybetweenconventionalstaticcompression,dynamiccompressionmethod,andtheory;indeed,manyproblemscannotbeaddressedwithoutthecombinationofallthreeoftheseapproaches.Withtheprospectsforthecreationofnewfacilities,includingmajorradiationsources,manybreakthroughsareonthehorizon.

2.2 Scientific Discovery Challenges: Static Compression Science

2.2.1 Structure and bonding at high compressionBasedonrecentwork,wecurrentlyhavealimitedunderstandingofstructureandbondingincondensedmatteratveryhighcompressions.MakingmeasurementswithanaccuracyandresolutionequaltothoseattainableatambientconditionsoverabroaderrangeofP‐Tconditions,particularlyathigherpressures,willallowthedevelopmentoftrulypredictivetheory:anewparadigmforunderstandingcondensedmatter.Wewillextendthisknowledgeacrosstheperiodictableoverthefullrangeofpressureandtemperature,andextendchemistryfromvalencetocoreelectrons,effectivelytoexploreanddevelop“kilovolt”chemistry.

Ourknowledgeofmaterialsislargelybasedonunderstandingobtainedfromsystemsatnear‐ambientconditions.Becauseofthis,therearenumerousexamplesofintriguingandpoorlyunderstoodphenomena,nearlyallofwhichwerenotpredictedtheoreticallyorweresimplyunexpected.Amongthemanyexamplesaretherecentobservationsofthenovel(O2)4cluster‐basedstructureofdenseoxygen;theunprecedentedpolymorphismofNawhichexhibitssome11differentphasesandmeltingbelowroomtemperatureatmegabarpressures;andtheremarkablepressure‐inducedtransformationofbothLiandNafrommetaltoinsulator.Theoriginofthebehaviorinallthreepreviousexamplesattheleveloftrulypredictive,generaltheoryislacking.Currentstaticcompressiondataobservationsarebasedonphenomenaobservedtopressuresof200–300GPa.Whathappensathigherpressures,e.g.,at1TPaandbeyond?Therearenumerouspossibleotherapplications/fieldsforstatichigher‐pressurecompression,includingmaterialsscience,andplanetaryscience,astrophysics.

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2.2.2 New physics in cold dense matterTheorysuggeststheexistenceofnewphysicsinmaterialsatveryhighpressures(e.g.,0.5–1TPa)andlowtemperatures.Therearecurrentlynoexperimentaldatainthisregime;indeed,itislikelythatexperimentswillrevealaltogethernewphenomenanotpredictedbytheory.Achievinghigherpressurestogetherwithvariabletemperaturesandotherextremefieldsincombinationwithnewdiagnosticswillleadtoadeeperunderstandingofthenatureofmatter.Thenewphysicsthatwillberevealed,forexample,willdrivenewtheoryintothemechanismsofmagneticandelectronicorder.

Anexcellentexampleisthepredictedmetallicsuperfluid;itisaproposedmagnetictechniquethatwouldbeasignatureofthepredictednewstateofmatter:asuperfluidsuperconductor.Thefirstchallengeisreachingthecombinedpressures,temperatures,andfieldsneededandcontaininghydrogentoexplorethis.Thediagnosticswouldinvolveimagingthevortexmatterthatwouldbecreated,aspredictedbytheory.Beyondfundamentalphysics,therearenumerouspotentialimplicationsforenergy,planetaryscience,andastrophysics.

2.2.3 Fundamental thermodynamicsWecurrentlyhavealimitedunderstandingofthebasicthermodynamicpropertiesofmanymaterials,includingrelativelysimpleelementalsubstances,inthecurrentlyaccessiblemegabarpressurerange.Thesepropertiesincludephasediagramsofmanysystems,whereinsomecasesextremelylargediscrepanciesinmeltingtemperaturesexistbetweenstaticstudies,shockcompression,andtheory.Sinceeachoftheseapproacheshasitsownlimitations,andmoreimportant,mayexploredifferentphenomenaorstatesofmaterials(e.g.,stableversusmetastable,relaxedversusunrelaxed),theexistingputativediscrepanciesmayprovideevidencefornewbehaviorinmaterials.Excellentexamplesincludethemeltingcurvesofbcctransitionmetals,suchasTa.Bybridgingthecurrentgapsthatexistbetweenthesemethods,wewillfindsolutionstoapparentdiscrepanciesinphasestability,structures,transitionsmechanisms,anddynamics,andtherebydevelopanunderstandingofthegeneralphasebehaviorofmaterialsatextremeP‐Tconditions.Forthis,accurateinsituprobesofstructures,dynamics,andequationsofstateareneededuptomultimegabarpressures(e.g.,0.5TPa)andtemperaturesfrommillikelvinsto~1eV.

AnotherexampleoffundamentalthermodynamicsatextremeP‐Tconditionsisthenatureofequilibriumdefectsandgrainboundariesundertheseextremeconditionsinpuresystemsaswellasinterfacialphenomenoninalloys,composites,andcomplexmaterials.Sofar,therehasbeenverylittleworkonstudyinginterfacesdirectlyunderanydegreeofcompression.Aninterfaceathighpressureisaburiedinterface,sothemostprevalenttoolsofsurfacescienceareuseless.Interfacescurrentlymaybestudiedusingamonolayerofamaterialwithauniquesignatureorusingasurface‐sensitivespectroscopicmethodsuchassum‐frequencygeneration.Newinterfacesensitivestructuralprobesareneeded.Thescientificchallengesincludeunderstandinghowinterfacesandinterfacialinteractionsbetweensimilarordissimilarmaterialsareaffectedbyhighpressure,howinterfacialstructure(e.g.,interfaceswithhighsurfacefreeenergyversusinterfaceswithlowersurfacefreeenergies)changeswithpressure,andhowinterfacialreactivity(e.g.,thereactivityatthesurfaceofaheterogeneouscatalyst)respondstopressure.Theapplicationsinclude(1)lubricationresultingfromthebehaviorofthinlayersoflubricantsbetweensurfaces;(2)adhesion,

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adhesionfailure,andmaterialaging,e.g.,theinteractionsofadhesiveswiththesurfacesofmaterials;(3)catalysisandelectrocatalysiswherethestructuresand,therefore,reactivitiesofthecatalyticentitiescanbecontinuouslyvariedbytheapplicationofhighpressure;(4)controlofthestrengthofmaterialsbycontrollingthegrainboundarystructure;and(5)geoscienceandplanetaryscienceinwhichthisinformationiscrucialforunderstandingthelarge‐scalestructureandphysicalpropertiesofplanets,includingtheirevolutionanddynamicsoftheirdeepinteriors.

2.2.4 Time-dependent transformations Equilibriumphasediagramsandstabilityrelationsareonlyafirststep.Ingeneral,equilibriumpropertiesdonotadequatelydescribematerialbehaviorindynamicprocesses.Compression‐ratedependenceofphasenucleation,growth,melt,andmicrostructurearevitaltounderstandingandmodelingdynamicevents.Bypioneeringabroadrangeoftime‐resolveddiagnosticprobes(e.g.,withx‐rays,neutrons,orlasers),weneedtoselectivelyinterrogatematerialsduringpressure‐inducedtransitionswiththeprecisioncharacteristicofstaticcompressiontechniques.Suchmeasurementswillproviderate‐dependentkineticphasediagramsandestablishanexperimentalbasisforimplementingpredictivecapability.

Developmentofafundamentalunderstandingoftheinfluenceofkineticsandcompression‐ratedependenciesofphasetransitionwillhaveaprofoundimpactonhigh‐pressurescienceandtechnology.Measurementandstudyofkineticphasediagramsarecrucialtounderstanding,modeling,andsimulatingdynamicprocesses.Asamaterialisdynamicallydrivenacrossaphaseline,thenucleationandgrowthkineticsarethecriticalparametersdeterminingthedevelopmentofthenewphase.Indeed,atexceedinglyhigh‐compressionrates,thematerialmaytransformtoaltogethernew(e.g.,amorphous)phasesratherthanthethermodynamicequilibriumphase.Experimentaldataregardingkineticsathighpressuresisverylimitedandcrediblepredictivetheoreticalapproachesdonotexist.Pressure‐driveswithprecisecontrolandtunabilityacrossabroadrangeofpressures,temperatures,andcompressionsrateswillprovidecrucialdataforestablishinginsightsintothischallengingareaofresearch.

Thisworkwilladdressthelargelyunexploredareaofphasetransitionkineticsanddynamicsandwillbevaluableindevelopingmodelsofmeteoriticimpacts(geophysics)andotherimpactphenomena(DOE/NNSAandDoD).Controlofphasetransformationkineticsdirectlyimpactsthemicrostructureandassociatedconstitutivepropertiesofmaterialsfortechnologicalapplications.Inaddition,athigh‐compressionrates,thepossibilityexiststhatthesynthesisofmaterialswithuniqueidentificationofnovelmetastablematerialsalongreactionpathscouldhaveimportanttechnologicalandgeoscienceimplications.

2.2.5 High-pressure strength, plasticity, and rheologyMaterialresponseundercompressionisafunctionofchemistry,phasecontent,microstructure,defects,impurities,aswellaspressureandloadingrate.Bydevelopingnovelx‐raydiffractionandnano‐imagingtechniquesandpressuredeviceswiththeabilitytoapplycontrolledandcharacterizeduniaxialorshearstraininwellcharacterizedenvironments,wewillquantifythecompletestressstateinmaterialsexposedtohighpressureandthedeformationmechanismsandflowstressasafunctionofstrainrateandacrossgrainboundaries.

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Thelimitedstatic(orquasi‐static)high‐pressurestrengthmeasurementsperformedtodaterelyonassumptions(e.g.,magicangleanalysis,peakbroadening),anddonottakeadvantageofnewdevelopments(e.g.,emergingnanobeamprobesandimagingmethods).Requiredarenewimagingtechniquesasafunctionoftime,whichwillrequireinturnadvancesinanvilcelldesigns.Thesedesignswillpermitpre‐definedandcontrolledloadingpaths,directnanoimagingofthestressstatewithnanometerresolutionatnanosecondtimescales,3Dtomographicmappingofstrainofgrainsincompositematerials,andfulldefinitionofthestressstateasafunctionofmaterial,pressure,andloadingrate.Determinationofstresstensorsacrossmaterialmicrostructuresasafunctionofhydrostaticanddeviatoricstressesprovidescriticalinputtotheory,modeling,andsimulation.TheresultswouldpotentialprovidethebasisfornewphysicallybasedmodelsforhighP‐Tstrength,includingstrainratedependence.Thisinformationisofcrucialimportanceforweaponsphysics,buttherearealsoprofoundimplicationsforgeoscience,astrophysics,andplanetaryphysics.

2.2.6 Synthetic chemistry frontierPressurecanbeusedasanovelreactivevariableinchemicalsynthesis.Byinterrogatingintra‐andintermolecularbondcharacteristicsusingnovelx‐rayandopticalspectroscopies,byutilizingtime‐resolvedprobesfollowingcompression,andbyusingtheorytodeveloprecoverystrategiesandelucidatingthermodynamicpathdependencies,wewillpredictandcontrolchemicalreactionofnovelmaterialsandtherebydevelopabetterunderstandingofthedeeperintramolecularandintermolecularinteractionsunderextremeconditions.

Asonethelargestrangesofanyexternalvariable,pressurecanbeusedasatoolor“catalyst”foraffectingnewchemicalreactionsandbondingconstructsnotobservedunderatmosphericconditions,openingupintriguingpossibilitiesforthediscoveryofnewmatterandnovelmethodsofsynthesis.Pressureincreaseslocalreactantconcentrations,producingmolecular(steric)configurationsthathavebeenshowntoinfluencetransitionstatesorintermediates,andresultantproductspeciesalongthereactioncoordinate.Thecombinationofcontrollableandwell‐definedhigh‐pressure/temperatureconditionsofferedbymodernhigh‐pressurecellsdevices,combinedwithadvancedtoolsforprobingthesemolecularstatesalongthereactioncoordinate,suchasopticalandvibrationalspectroscopies,x‐rayspectroscopies,andx‐rayandneutronscatteringmethodsoffersexcitingpossibilitiesforcontrollingchemicalreactionsanddiscoveringordesigningnewmaterialsundertheseconditions.

Thechallengestoprobingchemicalreactionsunderhigh‐pressure/high‐temperatureconditionsincludesmallsamplevolumes,thepotentiallylowthresholdsformaterialdamagesubjectedtoionizingradiation,alackofmethodsfortemporally‐controlledpressurizationcombinedwithtransientprobesofbond‐breaking/makingsteps,anddearthofin‐situtechniquestypicallyusedinthechemicalsynthesislaboratorywithinhigh‐pressuredevicesintheabsenceofrecoveryandpost‐mortemanalysis.Structuralrelationshipsforawidervarietyofchemicalfunctionalitiesunderarangeofhigh‐pressure/temperatureconditionsandpathwaysareneeded.Thisfundamentalknowledge,combinedwiththeoreticalcalculationsofhigh‐pressurereactantsurfaces,couldeventuallyleadtorationaldesignofsynthetictargets,muchlikethecurrentstatusofthefieldof

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organicchemistry.Hereagain,wemustmovefromobservationtocontrol,anapproachthatsofarisessentiallylackinginhigh‐pressurechemicalsynthesisatpressuresabove1GPa.

2.2.7 Optimized new materialsAsindicatedabove,highcompressionhasthepossibilityofcreatingnew,quenchablematerialswithenhancedpropertiesandfunctionality.Byusingthealteredbondedstatesundersuchconditions,wewillcreatenew,usefulmaterialsthatarerecoverableto,andstableat,ambientconditions.Combinedwithdevelopmentsintheorytopredictmaterialproperties,suitablecatalysts,andrecoverypathways,wewilldevelopnewmaterialswithenhancedsuperconducting,magnetic,thermoelectric,hydrogenstorage,solar,andphysicalproperties.

Thehighesttemperaturesuperconductingtemperaturesarefoundunderpressure.Forexample,theHg‐Ba‐CacupratehastheTcof164Kmeasuredin30GPa;however,thehighTcdoesnotpersistwhenrecoveredtoambientpressure.Cantheseactivemechanismsbeunderstoodandharnessedunderambientormoderatelycoolenvironments?Otherpossibilities,suchas“green”hydrogenstoragebasedonH2Oices,andthepredictionandcreationofvariousultra‐hardmaterials,somewithpropertiessuperiortodiamondareexpectedtobepossibleinthefuture.Itisknownthatdoubleandtriplebonds,forexample,areparticularlyactiveunderhigh‐pressureconditions.Polymerizationreactions,drivenbyelectronicinteractions,occuras“reactants”andarebroughtintoclosercontactwithappliedpressure.Smallmolecules,suchasN2,anditsisoelectronicrelativeCO,havebeenpredictedandshowntopolymerizeundermoderatepressures.ApolymericformofCOhasbeenrecoveredtoambientconditionsandshowntobehighlyenergetic,decomposingexothermicallytogaseousCO,andofferingtheexcitingpossibilityofnewclassesofexplosivematerials,preparedintheabsenceofcatalystsandsolvents.Stillotherexamplesincludetherecentcreationofbulkmetallicglassesunderpressureandtheprospectofmakingothertypesofglassesbasedontheobservationofpressure‐induced“polyamorphism.”Forthese,thechallengeistherecoveryofthesematerialsinlargequantitiesforusefulapplications.Thereareobviouslysignificantimplicationsformaterialsscience,energyscience,andnationalsecurityscience.

2.2.8 Radiation-induced high-pressure chemistryIonizingradiation(e.g.,x‐rays,visiblelight,neutrons,andprotons)canbeusedasanovelsourceofelectronicrearrangementinchemicalsynthesisaswellasanunwelcomemechanismofdamage.Bypredictingbondionizationforthesynthesisofdesiredproductswithagivenfunctionality,andbyinvestigatingmolecularbondbreakingviatime‐resolvedx‐rayandopticalspectroscopies,wewillbeabletodesignchemicalreactionstotargetnovelmaterialsaswellascalibrateandevencontroldamage.

Understandingthebehaviorofmaterialsunderextremeconditionsofhighpressureandhighradiationfluxisvitalforunderstandingandimprovingtheperformanceandreliabilityofnuclearweaponsandnuclearreactorcomponents.Inaddition,assomanystudiesofmaterialsareconductedusinglasers,neutrons,andx‐raybeamsaspartofcurrentandnextgenerationsources,itisvitaltoquantitativelycalibrateandassessthedamagecausedbyionizingradiation.Wehavediscoveredthattherateofdamagefromx‐raybeamshasastrongandreproducibledependenceuponthepressure(atleastinthecaseofTATB,

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slowingwithpressure),whichsuggeststhatmaterialscanbestudied,despiteradiationdamage,bysubjectingthemtosufficientpressuresorusingtime‐resolvedprobes.

Techniquesusedtostudyradiation‐inducedchemistrytodateincludewhitebeamenergy‐dispersivex‐raydiffraction,x‐rayRamanspectroscopy,andmonochromaticangulardispersivex‐raydiffraction.Samplesareinterrogatedbothbeforeandafterradiationbombardmenttoassessmechanismsandratesofdamage.Thechallengewillbetodevelopadditionalprobesandtousediagnosticinrealtimetodetermineatomicandelectronlevelmechanismswithvaryingsources(light,neutrons,varyingenergy,varyingx‐rayflux).Thebenefitsofthisworkwouldbetwofold:(1)developingquantitativebenchmarksforradiation‐induceddamageinmaterialsand(2)usingvariouskindsofradiationincombinationwithpressure,temperature,andotherfieldsfortherationaldesignofnewmaterialswithnewpropertiesandfunctionalities.

2.2.9 Earth science, planetary science and astrophysicsStaticcompressionscienceiscreatinganever‐expandingpicturewindowofincreasingclarityandresolutionontheinteriorsofourplanet.Despitethisadvancingvision,manyregionsoftheEarthremainpoorlyunderstoodintermsofmaterialproperties.AnexcellentexampleistheEarth’score.Thisregionoftheplanetismainlycomposedofiron,butinastatethatisfardifferentfromtheelementfoundnearthesurfaceoftheplanet.Ironhasinteresting,ifnotunusualpolymorphism,elasticity,andstrength;therearedramaticchangesinchemicalandmagneticproperties,andironisevenasuperconductorunderpressure.Weneedtounderstandnotonlythehigh‐densitysolidphases,butalsothefluidstatestopressuresabove350GPa.ThisinformationiscrucialformodelingtheEarth’smagneticfieldanddeterminingthetemperaturedistributionandheatflowfromtheinterior.

Anotherrichareaofstudyisthecore‐mantleboundaryregion,whereoxideandsilicatephasesexistthatareneverseenontheEarth’ssurfaceandhavecompletelydifferentphysicalandchemicalpropertiesfromnear‐surfacerocksandminerals.Moreover,advancesinobservationalplanetaryscienceandastronomyhaveledtomaterialsquestionsaboutbodiesthroughoutthecosmos.Byreachinghigherpressuresandtemperatures,andbymakingaccuratedeterminationsofthephysicalandchemicalpropertiesofplanetarymaterialsatsuchconditions,wewilldeterminethestructure,composition,dynamics,andevolutionofthefullrangeofplanetarybodiesandotherastrophysicalobjects.Thiswillhaveprofoundimplicationsforourcurrentunderstandingoftheevolutionofsolarsystemsandthepossibilityoflifeelsewhereintheuniverse.Planets,stars,andotherastrophysicalbodiesarenaturalhigh‐pressurechambers,sointerpretingthewealthofnewgeophysicalandastronomicaldataintermsoftheircomponentmaterialswillalsoaddnewunderstandingofinformationthatisimportantforfundamentalphysics,chemistry,andmaterialsscience

2.2.10 Life in extreme environmentsWedonotcurrentlyknowthelimitsoflifeinextremeenvironments.Bydevelopingnewmethodsformakinginsitumeasurementsofstructure‐functionofbiologicalsystems,fromwholecommunitiesoforganismstocomponentmolecules,wewillbeabletodefinethehabitablezoneinthecosmos,thelimitsoflifeonEarth,thepossibleoriginoflife,new

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methodsfordirectedevolution,andtherebydevelopthenewfieldofhigh‐pressuregenomics/proteomics.

2.2 Technical Grand Challenges in ‘Static’ Compression Science

2.2.1 Reaching 1 TPa and beyondTherecentdramaticimprovementsinhigh‐pressuregenerationandextremeconditiondiagnosticcapabilitiesareclearlyleadingtoimportantscientificadvances,butthisisonlythetipoftheiceberg.Achievingpressuresexceeding1TPa,farbeyondthecurrentcapabilityof~400GPa,willenablestudiesinentirelynewregimesofphysics.Novelhigh‐pressureapparatusdesignandmaterialsareneededtoextendcurrentpressureslimits.Newanvilmaterials,forexample,couldbebasedonCVDsinglecrystal,nanocrystallinediamond,andnewtypesofcomposites.Usinganano‐focusedx‐raybeamtomeasureanvilnanostrainstogetherwithlargesyntheticdiamondwithenhancedphysicalproperties,forexample,wewilloptimizepressurecelldesign.Suchbreakthroughswillenableopenextremecompressionlaboratoryenvironmentstomyriadofdiagnostictoolsavailableinstaticcompressionstudiesandheraldnewunderstandingofmatterunderextremeconditions.

2.2.2 Developing multi-probe ‘intelligent’ devicesThenextgenerationhigh‐pressuredesignsthatwillextendpressureslimitsto1TPaandbeyondwillrequiretailoredanvilsthatenablethemeasurementofabroadrangeofphysicalpropertieswithhighspatialresolution.Extensionoftailoreddesigneranvilscanmeasurenewphysicalproperties,includingelectricalconductivity,thermalconductivity,andNMR.Nano‐scalemanipulationandsub‐micronpatterningandmodificationonanvilswillresultinadramaticextensionofmeasurementsthatwillbeenabledinextremeenvironments.Theresultscouldalsoleadtonovelnanosensorswithapplicationsbeyondextremeenvironments.

2.2.3 Stress-strain states and P-T calibrationAccuratecharacterizationofthestress‐strainstateofmaterialsiscentraltoallaspectsofhigh‐pressurescience;italsounderliesthechallengeofcalibratingpressureasonereachesevermoreextremeconditions.Withthedevelopmentofmulti‐diagnosticprobes,“abinitio”calibrationsofpressurecanbedeveloped(i.e.,bymeasuringbulkmodulusanddensityonthesameloadingstate).However,wecannowgomuchfurtherandproducedetailedmapsofthemicro‐strainsinsamplesfromwhichthe3Dstressdistributionscanbedetermined.Thedevelopmentofmicro‐focusingcapabilitiesiscrucial.Nano‐focusedx‐raybeamwillallowmeasurementsofnanostrainsinnotonlytheanvilsandgasketsbutalsothesamplesandpressure(stress)calibrants.Suchhigh‐spatialresolutionprobescanmakedetailedmappingofmaterialproperties.Newtheoryandmodelingofcompositematerialsisneededtoproviderobustandreliablestress‐straininversions.Accuratecalibrationoftemperatureatveryhighpressureisalsoneeded;thiscalibrationneedstobecarriedoutbycombiningstaticanddynamiccompressionandtheory.Addressingthesetechnicalchallengesisrequiredinordertoopenextremecompressionenvironmentstothemyriadofdiagnostictoolsavailableinstaticcompressionstudies.

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2.2.4 Advancing x-ray methodsInelasticx‐rayspectroscopiessuchasx‐rayRamanSpectroscopy(XRS),x‐rayabsorptionspectroscopy(XAS),x‐rayemissionspectroscopy(XES),extendedx‐rayabsorptionfinestructure(EXAFS),nuclearforwardscattering(NFS),andnuclearresonantinelasticx‐rayscattering(NRIXS)willbeharnessedtointerrogatedeepcore‐levelbondingchangesandphonondensityofstates(DOS)determinationsunderextremeconditions.UsingtechniquesrootedinthephononmodulationofMossbauernuclearenergies,thephonondensityofstatescanbedetermined.IntheXAS,XES,andEXAFStechniques,valenceelectronicstatesareprobedbyphotoelectronabsorptionandemission.TemperaturecanbedeterminedbyappropriatefitsofthephononDOS,whichcanallowpotentialnovelmethodstoascertainsampletemperatureunderextremeconditions.Forexperimentsperformedtodate,Begasketsareusedtoallowx‐raysintoandoutofsampleregion.Thereisalsolikelytobesampledecompositionwithbombardment.XESisusuallyachievableforprimarilyheavieratoms.XRSrevealsbondingchanges(e.g.,hybridizationalteration)underextremeconditions.XASandXESprovideameasureofchangesinvalenceanddeeperelectronicchanges(cf.,“kilovolt”chemistry).Thoughthesearenowestablishedtechniques,themeasurementsare,ingeneral,photonlimited.

NRIXSandNFSmeasurementsareonlypossiblewithhighfluxsourcesduetotheirinherentlowsignalsforconventionalhigh‐pressure‐sizedsamples(nanoliters,cubicmicrons)andtherequirementforhighlyfilteredx‐raylightusingdoublemonochromatorstoachievemeVenergyresolution.Thus,longdetectiontimesarerequiredduetolowsignaltonoise;moreover,measurementsatthehighestpressuresareimpossiblewithcurrenttechnologybecausethesignaloverwhelmsthebackground.OnlyMossbauer‐sensitivenucleicanbeused(NRIXSandNFS).Mostmeasurementscannotbeperformedoverthewiderangeofpressuresneeded(e.g.,multi‐megabarpressures)orwithsufficientspatialresolutiontoaddresstheabovesciencechallenges.Hence,higherbrightnessx‐raysourcesarerequired.

2.2.5 Real time x-ray imaging with nm resolutionTheabovedualadvancesinx‐rayspectroscopiesandtime‐resolvedmethodsneedtobecombinedultimatelyforinsitutime‐resolvedimaging.Suchimagingmethodsareessentialforunderstandingthetimeevolutionofdefectsinmaterials,startingatthesubpicosecondscale.Anotherexampleisthetechnologicalchallengesforstudyinginterfacesathighpressure,whichstemsfromissuesofsensitivity,i.e.,detectingasmallnumberofinterfacialspecies,andselectivityandsuppressingthebackgroundoftheassociatedbulkmedia.Forplanarinterfacesburiedwithinopaquemedia,suchasbimetallicinterfacesinmetal,grazingx‐rayscatteringcouldbeuseful.Butforburiedopaquecomplexinterfaces,suchasthegrainboundariesinsideapolycrystallinemetal,goodtechniquesdonotyetexist.Onesuggestedpossibility,basedontheparadigmofnonlinearoptics,mightbetheuseofnonlinearx‐rayopticsusingintenseshort‐durationcoherentx‐raypulses,forexample,imaginggrainboundarystructuresusing2‐photonx‐raymicroscopy.

2.2.6 Neutron scattering to multi-megabar pressuresNeutronsarecomplementarytox‐rays,astheyprobenuclei(notelectrondistributions),magneticstructure,aresensitivetohydrogen,andhavehighpenetratingpower.However,neutronscatteringstudiesarecurrentlylimitedto~30GPabytheneedtouselargesamplevolumestoovercometheinherentweaknessofneutronsources.Byusingmicro‐focused

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neutronbeams,higher‐intensityneutronsources,andlargersamplevolumesavailableusingnovelpressurecelltechnologies,neutronscatteringmeasurementscanbeperformedtoabove100GPa.Thegoalisaccuratemeasurementstoatleast300GPatoaddressthescientificchallengesdescribedabove.Thesemeasurementsincludebothelasticscattering(e.g.,diffraction)aswellasthemoredifficultinelasticscattering(e.g.,spectroscopy)measurements.Meetingthesechallengesrequiresadvancesinbothhigh‐pressureapparatus(e.g.,largersamplevolumes)andsignificantincreasesinneutronflux—notincrementally—butbothbyordersofmagnitude.Suchadvanceswillenablethenumerousstrengthsofneutrontechniquestobeextendedtoextremecompressions.

2.2.7 Challenge of liquids and amorphous materialsTheinherentweaknessofscatteringfromliquidsandamorphousmaterialshaslonglimitedtheirstudy.Yetawiderangeofnovelextreme‐conditionsphenomenaexistsinsuchmaterials,includingbothpolyamorphismandliquid‐liquidphasetransitions.Wecurrentlyhavealimitedunderstandingofthenatureofamorphousmaterialsunderhighstaticanddynamicpressures.Howaretheatomsormoleculesdistributedspatially,andwhatistherangeoflocaldensityvariations?Whatnewprobescanbringinsightsintoliquid‐liquidtransitionsandmeltingphenomenaathigh‐pressureconditions?Howcanmeltingbedefinedordetermined(formetals,smallmolecules,etc.)?Likewise,second‐ordertransitionsbetweenamorphousphases,suchasglasstransitionsinpolymers,aredifficulttodiscernwithcurrenttechniques.Methodssuchasneutronandx‐rayscattering(SANS,SAXS,pairdistributionfunction)currentlygiveinformationaboutthedistributionofatomicpairsinamorphousorliquiddomains,butthescatteringcross‐sectionsarelow,signalsareoftendifficulttodistinguishfromdiamondComptonscatterorotherbackgrounds,andanalysisisdifficult.Acousticmeasurementsusedtoderivebulkvolumetricinformationarefrequencydependentanddonotofferatomic‐levelinsightsintocompressiveresponses.

ThisareaofstudywillrequiredevelopingnoveldetectortechnologiestoenableinelasticComptonscatteringtoberemoved,extendingneutronscatteringtechniquestohigherpressures,andusingnano‐imagingtechniques.Forexample,newmethodsareneededwithenhancedsignals(orenhanceddetection)forinterrogationofamorphoussamplesathighpressuresinsmallsamplevolumes,coupledwithhighaccuracyknowledgeoflocaltemperatureandstressstates.Potentialimprovementscanbegainedfromback‐drillingthediamondanvilsalongtheincidentx‐rayaxis,useofslits,orincreasedflux.Likewise,neutronscatteringmeasurementswithsmallerfocusedbeamsinlargevolumesatevenhigherpressures,asdiscussedabove,willopenupalargenumberofpotentialmeasurementsonamorphousphases.Themeasurementsmustbecoupledwithmodelingeffortsaimedatcapturingandinterpretingthestochasticnatureoftheseformsofmatter.Finally,extendingthesenewtoolstothetimedomainandcombiningthemwithtransientmeasurementsoftransportproperties,viscoelasticproperties,andkineticsofliquid‐liquidandliquid‐solidphasetransformationswillbenecessaryforinterpretingthedynamicaspectsofphasediagrams,improvingequationsofstateforamorphousormultiphasematerials(includingmelt),andevaluatingbondinginnewformsofmatter.

2.2.8 Filling the strain rate gap: Static to shockInterestingandlargelyunexploredphysicsliesbetweenthestaticanddynamictime‐scalesathighpressure.Modetransitions,aswellasphasetransformationkinetics,areknownto

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bestrongfunctionsofloadingrate.Bydevelopinghigh‐pressurecellswithpreciselycontrolledandcalibratedloadingratescapableofcompressionratesto105,cyclesatkHz,andsingle‐shotrapiddecompression,andbydevelopingdetectorsandprobesconsistentwiththesenewexperimentalcapabilities(sub‐micronspatially,subnano‐secondtemporally),wewillelucidatetherate‐dependentpropertiesforthefirsttime.

Systematicstudiesofphasetransitionscanbeachievedusingtunableprecisepressure‐drivesinconjunctionwithtime‐resolveddiagnosticprobes(e.g.,x‐ray,neutron,andlaser).Thetime‐resolvedprobecanbesynchronizedandtimedtoselectivelyinterrogatethesampleasitisdrivenacrossthephasetransition.Thedynamicdiamondanvilcell(dDAC)isoneexampleofatunablepressure‐drivesuitableforthesetypesofstudies.Pulse‐selectionhardwareandhigh‐speeddetectorsathigh‐performancesourcesarenecessarytechnicalcomponentstoperformtheseproposedstudies.

2.2.9 Transport propertiesTherearefewmeasurementsofthermalandtransportpropertiesathighpressures/temperatures.Examplesofdesiredmeasurementsincludethermalconductivity,diffusivity,andviscosityinsmallvolumesathigh‐pressure/temperatureconditions.Thepresentstate‐of‐the‐artconcernstheuseofdesigneranvilsforresistivitymeasurements,NMRandrolling‐ballviscositymeasurementsatlowpressures,andlaser‐basedfoilheatingmethodstoestimatethermalconductivities.Thesechallengescouldbemetwithadvancesinpulse‐probeNMRmethods,developmentofnon‐magneticdiamondcellscapableofhighpressures,exploitationofconfocal,ultrafastopticalmethodsforbothheatinganddetectingtemperaturechangesspatiallyinhigh‐pressuresamplevolumes,anddesignofnewembedded‐probeanvilsformeasuringheatflow.

2.2.10 Thermochemical measurements at multimegabar pressuresInadditiontoconstituitive,transport,anddynamicalmeasurements,thereremaingreatchallengesinmeasuringfundamentalthermochemicaldataneededtoaddressthesciencechallengesdiscussedabove.Newtechniquesareneeded,forexample,todeterminefreeenergies,enthalpies,entropies,andheatcapacitiesofpure,complex,andnanophasematerialsstartingatevenmodestpressures.Acombinationoftime‐resolvedopticalmethodscombinedwithhighlysensitivenanolithographictechniquesneedtobedevelopedformeasurementstobeperformedinconcertwiththeinsitustudiesdescribedabove.

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3. Dynamic Compression Science Dynamic compression science has historically been a field in which measurements havebeen made (primarily) at the bulk or continuum level. Details of the effects of phasetransformations,defectgeneration,chemicalcomposition,shock‐inducedchemistry,andtheeffect of grain boundaries and grain orientation on dynamicmaterial response have onlybeeninferredthroughwaveprofileanalysisand/orpost‐experimentexamination.Thatsaid,thelevelofdetailgatheredinthefirstdecadesofcompressionsciencewasadequateforthesimulationandmodelingcapabilitiesavailableatthetime,andtheweaponscommunitywasabletodesignmodernweaponsystemsthroughacombinationof“simple”simulationandexperiment.Thisisnolongerthecase.Today, we are on the verge of transforming dynamic compression science from sciencefocused on developing understanding at the continuum level to a scientific disciplinefocused on developing understanding at the atomistic and mesoscopic scales, ultimatelyleading to the linking of scales and the ability to predict and control performance underdynamic loading conditions. Our current modeling and simulation capabilities haveunprecedented temporalandspatial resolution:a resultofmodernplatformdevelopmentandbetterunderstandingofmaterialresponse(thoughwehavenotyetreachedsimulationlinking all scales), but we have not reached our goal of fully predicting and controllingmaterial response. Reaching this goal will require a suite of new diagnostic tools andcapabilities that can help answer the scientific challenges, described below, and providevalidationdatafornextgenerationsimulationcapabilities.Wewillnotsucceedifwedonotmeetthesechallengingopportunities.

3.1 Scientific Discovery Challenges: Dynamic Compression Science

3.1.1 Kinetics and mechanisms of melting, freezing, and solid-solid phase transformations Along‐standingproblemincompressionscienceistheidentificationofthelocation(inPressure‐Volume‐Temperature[P‐V‐T]space)andcharacterizationofphasetransformations,includingmelting,freezing,solid‐solidtransformations,andtheirassociatedkineticrates.Ofconcernisthefactthestaticanddynamicmeasurementsdonotalwaysyieldthesamelocationinphasespace.ThiscouldbearesultofdifferencesassociatedwiththetransformationpathdependenceinP‐V‐Tspace,and/ortheeffectofstrainrate(whichcanincludebothloadingandreleasepaths)onthetransformationdynamics,orsimplythatthesamplemustbesuperheatedduringshockexperimentstoobservethetransformationonthetimescaleoftheexperiment.Moreover,wehaveveryfewtechniquesforcharacterizingphasetransformations,particularlydynamically.Inprinciple,pyrometrictechniquesshouldyieldcharacteristicsignalsassociatedwiththetemperaturearrestthatisindicativeofaphasetransformation,andtransientX‐raytechniquesshouldprovidestructureinformationthatultimatelycouldbequantifiedtoyieldfractionalphasesasafunctionoftime.Neithertechniquehasreachedamaturitylevelthatunambiguouslymeetsourneeds,andthedatawillbeunimportantifourtheoreticalconstructsregardingtransformationareinadequateoratbestphenomenological.Thus,inadditiontoadvanced

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diagnostictools,werequirethedevelopmentoftheoriesthataccuratelyrepresentthephysicsoftransformationsandcapturethepathandratedependenceeffects.

3.1.2 Warm dense matter (WDM): metallization, release around critical points Themetallizationofmatterwhensubjectedtoextremesoftemperatureandpressurehasbeenconsideredandpursuedsincethedevelopmentofbandstructuretheoryandtherecognitionthatextremepressurecouldcauseaclosureofsuchbands.Thatsaid,metalscanalsobehavecounter‐intuitively.Forexample,lithiumandsodiumcanbecomeinsulatorsundertheextremesofpressure.Perhapsmoreimportantly,theclassofmatterknownaswarmdensematter(WDM)liesin“no‐man’sland.”ItisnothotenoughfordirectapplicationofThomas‐Fermi,yettoohottoaccuratelycalculatethepropertiesusingclassiccold‐curvetechniques.Moreimportant,wehaveveryfewmethodsforcreatingandcharacterizingsuchmatter,bothoninitialcompressionandsubsequentrelease.Asanexample,ifonecouldreliablymeasuretheconductivityundertheseuniqueconditions,whilesimultaneouslymeasuringthetemperature,pressure,andvolume,thedatasetobtainedwouldchallengeandexpandourcurrentthinkingregardingtheequationofstate(EOS)ofmatterinthisregime.Furthermore,ifwecouldcreatecomparableconditionsinastaticsetting,wecouldmakeaconnectiontobetweenstaticanddynamicregimesthatwillimproveouroverallunderstanding.Thus,thereisasignificantneedtodevelopcapabilitiesforcreatinganddiagnosingthisstateofmatter,bothtodevelopafundamentalunderstandingofsuchthingsasthenatureofmatteratthecoreofplanets,butalsotogainanunderstandingthatcanimpactapplicationssuchasfusion,first‐wallmaterialstudiesfortheInternationalThermonuclearExperimentalReactor(ITER),andenhanceourunderstandingofnuclearweaponperformance,includingboost.

3.1.3 Evolution of microstructure under dynamic loading including defect distributions Mostmetallicmaterialsarepolycrystallineinnature,suchthattheyareanaggregatecompositeofmetallicsinglecrystals.Asthepolycrystalisdeformed,thesinglecrystalsinteractwitheachothersothattheinternalstresswithinthepolycrystalishighlynon‐uniform.Simulationspredictafactoroftwoorsodifferencebetweentheminimumandmaximumstresswithintheaggregate.Ifthesematerialsaredeformedagreatdeal,thetemperaturewillcertainlyincrease,andtheybegintodevelopdamagedregionsandfailurezones.Thelocationofthesedamagedandfailedregionsishighlydependentuponmicrostructuralcharacteristics(e.g.,grainsizedistribution,impuritycontent,grainboundarystrength)andthenatureoftheloading(e.g.,timerateofloading,totalstrain,maximumstress).Figure1showsanimageoftantalumdeformedbyplateimpactloading.Thisimagedisplaysasnapshotofamaterialthathasfailedbytheprocessofporenucleation,growth,andcoalescence(aductileprocess).Notethatthefailedregionsarespreadoutandindicatethatthephysicalprocessesinvolvedarestochasticinnature.

Predictingwhenandwherematerialfailurewilloccurwithcurrenttheoreticalandcomputationaltoolsisstilloneofthebiggestchallengesfacingthematerialmodelingcommunity.Failureisthefinalstepinacomplexphysicalprocessofmicrostructuralevolution.Theabilitytounderstandandpredictwhenandwherefailurewilloccurforanytypeofaggregatematerial(e.g.,polycrystallinemetals,highexplosives,concrete,fibrouscomposites,etc.)requiresthatwenotonlyunderstandthestatisticsofmaterialinitial

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conditionssuchasgrainsizeandmorphology(forthecaseofpolycrystallinemetals),inclusioncontentandlocation,grainboundaryshape,misorientationacrossgrainboundaries,etc.,butalsohowthesequantitiescombineandevolveunderserviceenvironmentsleadingtofailure.Deformationeventsthataddtotheinitialheterogeneityare

suchthingsasinhomogeneoustemperaturechange,dislocationcellformation,slipbandformation,twinning,andphasetransformation.Furthermicrostructuralevolutionleadstodiscretedamage/failureprocesses,suchaspore(ductilematerials)orcrack(brittlematerials)nucleation,growthandcoalescence,shearbandformationandgrowth.Theseeventsalsooccurinthreedimensions,ofcourse,soweneedtopushourexperimentalandtheoretical/computationalcapabilitiestodeliverthistypeofinformationin3D.Atwo‐dimensionalcharacterizationwillneverallowustoachievesuccess.

Thus,wehavetheneedforanewexperimentalcapabilitytotrack,insitu,the3Dmicrostructural(includingdefectdistributions)andtemperaturefieldandtheirevolution.Theinformationisneededtocharacterizeanddevelopassociatedtheoriesthatincorporatethedetailsofdefectdistributionsleadingtoporenucleation,poregrowthandcoalescence,dislocationcells,slipbandsandtwins,aswellasshearbands.

3.1.4 Experiment/theory convergence: Developing the ability to reproduce simulations of ‘real systems’ for better understanding of experimental observations. Oneofourgreatestchallengesistobeabletoconductexperimentsandperformassociatedsimulationsthataresopreciseintheirinitialconditions(suchasthedefectdistributionand/orpolycrystallineorientationsandsizes)thatwearemodelingthe“real”andnotthe“ideal”system.Oneapproachwouldbedevelopexperimentsthatdirectlyevaluatetheresultsofmoleculardynamics(MD)simulations,suchasanLINACCoherentLightSource(LCLS)experimentwithexactlythesamenumberofatomsasanMDsimulation,andvalidatingattheappropriatelengthscale.Moreover,experimentsmightbedesignedtoprobeaparticularphysicalregimetoisolateandprovideameansforbettercomparisonwiththesimulations.Toooften,weendupcompromisingonboththeexperimentandthesimulation,withresultsthatneedinterpretationorspeculationtomaketheconnectionbetweentheexperimentandthesimulation.Thus,thedevelopmentofaseriesofexperimentsthatarestandardsand/orthechoiceofsimulationsthatwecanproperlydiagnoseinanexperimentiscriticaltodeveloprealunderstandingandtomovefrom“observationtocontrol.”

Fig.1.OrientationImageMapofadeformedtantalumplateimpactsample.

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3.1.5 Resolving the details of detonation and shock-induced chemistry It has been the firm belief of many in the Energetic Materials (EM) community that the key to predicting explosives behavior for both performance and safety lies in the intimate understanding of the molecular-level processes. Energetics are complex systems that involve inter- and intramolecular bonding, numerous morphologies, different polymorphs, crystal defects, impurities, and component inhomogenities. EM can be made stable under ambient conditions, can be stimulated to energetic decomposition, will crystallize into a knowable structure with a given density, and can be fabricated into incredibly elegant shapes and strong mechanical structures. The crystal structure and intermolecular bonding strongly affect the density of the material and, thus, the energy delivered per unit volume of explosive. The molecular structure and the intermolecular bond energies will also affect the rate at which energy put into a molecule might escape to the bulk material, which in turn strongly affects the sensitivity and safety of the compound. Unfortunately, these molecular-level processes are not known even for systems that lack many of the complicating factors listed above. Without this detailed data, we cannot develop molecular-level predictive capabilities. Present theories can only lump most of the chemistry into overall reaction rates or energy release rates. The overall goal is to develop a complete time-dependent description of detonation and the evolution of the product’s equation of state for military purposes as well as to facilitate the introduction of new energetic materials for military, counter-terrorism, surety, and industrial applications. These new energetic materials include explosives, rocket and gun propellants, and pyrotechnic devices. Various driving forces (which can be different for the wide variety of applications) include increased performance, increased safety margins, decreased cost, and decreased environmental impact. It is important to have optimal screening measures so that confident decisions can be made more rapidly on whether to proceed or not with a particular formulation. We need to develop the ability to screen, measure, and predict the performance of new or proposed materials for optimal use and/or unique applications.

3.1.6 Discovering new phases and forms of matter at ultra-high compression using tunable pathways and controlling reaction chemistry through pressure and temperature Asstatedintheintroduction,oneofthekeycontributionsofcompressionsciencehasbeenthroughdiscovery,asgeneratedbynovelextremesofpressureandtemperature.Forexample,thenatureofthephaseboundaryinsodiumandlithiumwascompletelyunderstoodwhentheexperimentelucidateditsconcavedownwardnature(inP‐Tspace)and,ingeneral,thatthenatureofbondingcansignificantlychangewithcompression(imaginecoreelectronparticipationintheextremes).Furthermore,chemicalreactionsthatareforbiddenonthegroundstatepotentialsurface(e.g.,Woodward‐Hoffmanforbidden)maybeaccessibleundertheextremesofpressureandtemperature.Thus,theexplorationofpotentialenergysurfacesasafunctionofpressuremayoffernewroutesforthesynthesisand/ormanufactureofmaterialsthatwouldotherwisebeunachievable.Theclassicexampleofthisistheconversionofgraphitetodiamondusingpressure/temperature,butotherexamplessuchastheformationofpolymericnitrogenhavedemonstratedtheutilityoftheseconcepts.Thus,usingabinitiocalculationsasguides,andthroughthedevelopmentofarobustexperimentalprogram(includingtheabilitytotunepressureandtemperaturethroughtheproperchoiceofwaveprofile,e.g.,ramp,shock,etc.),wewillbeinapositiontopredictand/ordiscovernewmaterialsthatmayhavefunctionalbehaviorthatmeetourneedsunderextremeserviceconditions(e.g.,armor,highneutronfluxesofreactors,etc.).

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3.1.7 Discovering and understanding of the partitioning between dissipative and non-dissipative mechanisms Theconceptofashockiswelldefined.However,theunderlyingprocesseswithintheshockwaveandthepartitioningbetweendissipativeandnon‐dissipativemechanismsarenotwellcharacterizednorwellpredicted.PredictingandmeasuringtheHugoniotElasticLimit(HEL)andstrengthunderloadingisamust.Wecurrentlyhavelittlemeansformeasuringandcalculatingtransportproperties,andtherefore,ourdescriptionoftheloadingprocessisincompleteandwecannotconnectwiththeory.Wemustdevelopdiagnosticsattheappropriatescale(e.g.,diffractionforatomic‐levelinformation)thatallowtheelucidationofmechanismsimportantinallrateprocesses,includingtransitionfromshocklessloadingtoshockcompression,andprovidephysicaldetailsthatresolvephenomenologicalmodelsofdeformationsuchastheSwegle‐Gradyfourthpowerlaw.Inadditiontobetterexperimentalcharacterization,wehaveaneedfortheabilitytopredicttransportproperties,damageevolution,andlocalizationphenomena.

3.1.8 Determine the role of shear in deformation processes Shearcanplayamajorroleininitiatingandcontrollingthephysicalandchemicalprocessesthattakeplaceunderdynamicloading,butneedstobequantifiedandbetterunderstood.Wecurrentlyhavelittleexperimentanddiagnosticcapabilitiesforresolvingshearsoastoascertainitsroleindynamicmaterialprocesses,includingchemicalreactions.Forexample,wewouldliketoknowthemechanismsthatcauseinelasticdeformation,damageevolution,andfailureandtheextenttowhichshearcontributestotheseprocesses.Experimentsdesignedtoexamineshearcontributionswouldprovidedatathat,inturn,wouldguidethedevelopmentofapredictivecapabilitybyprovidingamechanisticunderstandingofstructural,chemical,inelasticdeformation,fracture,andsecond‐orderphasetransitionsthatcanbedrivenbyshear.

3.1.9 Develop understanding of the role of interfacial boundaries Thereisalackofunderstandingoftheinteractionofwaveswithboundaries(includingspallation)andthestabilityofmaterials(orlackthereof)thatresultinthedynamicmixingofmaterialswithinlocalenvironments.Thus,wemustconductcontrolledexperimentswithhigh‐resolutiondynamicimagingtomeasurethevelocityfieldevolutionanddynamicmixingasafunctionoftime,whichwouldimplytheneedformeasuringflowwithinopaquematerials.Furthermore,thisinformationisoflittlevaluewithoutbasictheoriesforpredictionofthelocalgeometriesaswellasthermodynamicstatesinthemixedphaseregions.Themixedphaseregionsincludeheterogeneousinterfacesofgrainstructureandtheirevolution.Inaddition,weneedtounderstandthemorphology,sizeofparticulates,andtheirrelationtoglobalvariablessuchasdensityevolution.Finally,weneedtheabilitytodeterminematerialpropertiesfromobservationsofinterfacialevolutionundergeneralloadingconditions,whichwillallowustopredictandoptimizematerialbehaviortomeetourfunctionalrequirements.

3.1.10 Develop an understanding of the transition in material plasticity and damage evolution across the ‘thermally activated’ to ‘shock’ to ’drag control’ regimes Thereisalackofunderstandingoftheoperativemechanismsofdefectgenerationandstorageacrossthetransitionsfromthermallyactivatedplasticityunderuniaxialstressto

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uniaxialstrainshockloading.Furthermore,asweincreasestrainrate,thetransitiontodragcontroloccursasrelativisticeffectsbecomeoperative.Todate,onlysurfacediagnostictoolshavebeenappliedtostudyingthesefascinatingtransitionalregimesinplasticitywithlittleinsight.Accordingly,theoryhasnotachievedphysicallybasedmodelstoaddressthesetransitionsowingtoalackofmechanisticunderstandingofthechangesindefectgeneration,motion,andthereafterstorageprocessesasafunctionoftheappliedstrainrate.

3.2 Technical Grand Challenges in ‘Dynamic’ Compression Science

3.2.1 Characterization of melting, freezing, and solid-solid phase transformations Weneedtodevelopacomprehensivedefinitionofmelt.Weknowthatlossofshearmodulus,lossoflong‐rangestructure,andlossofautocorrelationareindicators,andweneeddiagnosticsthatconnecttothisdefinition.(Wealsorecognizethatthereisadistinctionfromamorphoussolids.)Toolsshouldincludethefollowing:

• Phonondispersionmeasurement—LCLSdiffractioncorrelationinstrument?

• Measurementofshearmodulus

• Fullyutilizeadvancedlightsources

• Coherentimaginganddiffraction

• Tomography(grainscalemicrostructure)

• Timeresolution(kinetics)

• Diffusescattering(statisticalrepresentationofdefects)

• Smallanglescattering(nucleationandgrowthkinetics)

3.2.2 Real-time diagnostics for dynamic mapping of the thermo-mechanical field Wehaveaneedtodeveloppredictivecapabilitythatdescribesthegenerationandevolutionofdefectsthatcontrolcontinuummaterialproperties.Wemustdevelopandfieldmultiplediagnosticsforsuchexperimentstoachievethermodynamicfieldmeasurements,inparticulartemperaturemeasurementsandspecificationofthefullstresstensor.Thesediagnosticsmustincludeinsitutemperatureandstressdiagnosticsapplicabletodifferentcompressionregimesandtimescales.Thiswillallowthespecificationoftime‐resolvedthermo‐mechanicalvariablesatdifferentspatiallocations.Thus,weneedthefollowing:

• Accuratetemperatureandstrain/stressfieldmeasurements

o Localenvironmenttemperatureprobes

o Multi‐axialstressprobes,e.g.,singlemoleculespectroscopy

o Multi‐axialstrainprobes,diffraction

• Pre‐andpost‐experimentcharacterization

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o Tomography

o DiffractionContrastTomography

3.2.3 Ability to make experimental measurements to link length scales ranging from atomic to continuum dimensions Continuumresponsedependsonmaterialbehavioratlowerlengthscales.Asuiteofinsitutime‐resolvedmeasurementsatdifferentlengthscalesisrequiredtovalidatetheoreticalmodelsastheytransitionfromonelengthscaletothenext.Toreachthisgoal(need),wemustdevelopnewexperimentalcapabilitiesthatprovidetheselinkages.Thelinkageofmeasurementsatdifferentlengthscaleswillleadtothefirstrealisticmodelsrequiredforpredictivecapability.

3.2.4 Ability to make in situ spectroscopic measurements including those of electronic structure Spectroscopicprobesprovideacharacterizationtoolformeasuringboththeaverageandlocalizedenvironmentaleffectsofcompression,dependingontheprobeanditspracticalimplementation.Dataregardingtheeffectofcompressiononmolecularstructureand/orchemicalchangescanbeobtainedthroughvibrationalspectroscopies(e.g.,RamanandIRabsorption),whileelectronicspectroscopiesprovideameasureofthechangesinconductivity(asmanifestedthroughchangesinFresnelcoefficients)andchangesinthepotentialsurface.Nuclearspectroscopies(e.g.,XANES/EXAFS)canalsoprovideinformationregardingbondingandnearestneighbors.Thus,modernfacilitiesmusthavecapabilitiesforimplementingthefollowingspectroscopiesinordertomakestrongerconnectionwiththeoreticalmodels:

• Reflectivity

• Raman

• X‐rayspectroscopy

• XANESandEXAFS

• XEL

3.2.5 Complex loading path control Asdiscussedpreviously,theapplicationofcompressioncanprovideroutestootherformsofmatterthatwouldnormallybesymmetrydisallowedorinaccessibleonthenoncompressedpotentialsurface.Thus,thepropercombinationoframpandshockcanprovidethemechanismfortuningthepathandcreatinganenvironmentconducivetogeneratingnewformsofmatterorfor“allowing”normallydisallowedchemicalreactions.Inaddition,theabilitytoquantifythepartitioningofenergybetweendissipativeandnon‐dissipativemechanismsrequirestechniquesthatallowforchangingtherelativecontributionsoftheseprocesses.Thus,ultimatelyachievingdynamicalcontroloftheseprocesseswillrequiretheabilitytocarefullytunetheloadingprofile,fromisentropictoshockloadingandanywhereinbetween,inordertovarythethermalcontentaswellasaccessportionsofthepotentialenergysurfacethatcanonlybeaccessedundercompression.

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3.2.6 Develop first-order continuum analyses that produce better subscale models and capture defect evolution Manyofthecurrentdescriptionsofdynamicloadingarephenomenologicalinnatureandcannotbeconnectedina“real”sensetothematerialworld.Asanexample,todesignoptimalexperimentsfordirectcomparison,wehaveaneedforrealisticdescriptionsofinelasticdeformationthatincorporatesmaterialphenomenaatlowerlengthscales(microstructure,defects,texture,etc.).Often,experimentalistsandtheoristsdefineexperimentsthatare“ideal”inthesensethattheyarecapableofbeingperformed,eventhoughtheexperimentortheorymaynotbemodeledortested.Thus,weneedstrongerexperimentalandtheoreticalcollaborationtodefineoptimalconditionsanddiagnosticsfromwhichtodrawmoreaccuratecomparisonsand,asaresult,abetteranalysisandinterpretationofexperiments.

3.2.7 Learn how to conduct and diagnose experiments relevant to 3D applications Real‐worldapplicationsareinherentlythree‐dimensionalandwillofteninvolvephenomenathatmaynotoccurinone‐dimensionalexperiments.Thus,wehaveaneedtodevelopexperimentalmethodsanddiagnosticsthatachieveandquantifycontrolled3Dloadingconditionsinsuchamannerastoallowinterpretation.Thisworkinherentlyincludesthedevelopmentofmaterialmodelsthatarepertinentto3Dloadinganddevoidofknobs,ifatallpossible.

3.2.8 Design experiments that overlap different loading regimes and experimental platforms Wecurrentlyhaveatourdisposalalargenumberofplatformsforconductingdynamicexperiments,withtheZmachineandNationalIgnitionFacility(NIF)asexamples.However,wehavenotdevelopedmethodsthatguidethebestuseofthesedifferentexperimentalplatformsandloadingregimes.Toachievemaximumeffectiveness,wemustlearnhowtocoordinateandintegrateexperimentsondifferentplatformsanddifferenttimeregimes.Whencoupledwithavarietyofvolume‐andtime‐scaleprobes(flexibilitytospanscalesonfacility),thesetypesofexperimentswillaidindevelopingtheunderstandingoftheloadpathandstrainratedependenceofmaterialpropertiesneededtoachieverealisticandcompletemodels.

3.2.9 Increase experimental throughput Weareoftenlimitedindynamiccompressionsciencebytherateatwhichwecanconductexperiments.Wemustworktowardthedevelopmentofnewexperimentalmethodsthatalloweasierandfastermeasurementsofdynamicpropertieswhilesimultaneouslydevelopingnewexperimentalparadigmsforcombiningmultiplediagnosticsthatyieldincreasedefficiencies,decreasedcost,andfasterturnaround.Thesenewexperimentalmethodswillallowforamorecompletesetofobservations,whichinturn,willincreasedevelopmentofrealisticmodels,therebyadvancingthefield.

3.2.10 Develop improved materials and standards for uniform comparisons Lastly, we have a need for the development of a set of standard materials that will allow us to connect measurements on a variety of platforms and using a diverse set of diagnostics. For example, loading a 50-micron thick tantalum sample on NIF may require the development and

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production of an extremely fined-grained material to ensure that the data is not dominated by grain boundaries. To make a direct comparison of this data with that obtained on guns may not be an easy task. To start, we should make gun measurements with the fine-grained material, but our results may still be confused with loading rates that may influence the shock wave rise time. They may be further confounded by time-dependent changes in the wave profile. One example is the change in amplitude of the elastic precursor simply as a function of sample thickness. Thus, connecting these disparate temporal and spatial regimes will require careful thought and analysis. Furthermore, if we could develop better impedance matching materials that are transparent, we could begin to imagine (nearly) looking in at the processes that are taking place in bulk. These observations will be required if we truly expect to achieve control.

3.3 Theory Needs and Challenges in Compression Science

Anaccuratematerialdescriptioninvolvesthecharacterizationofmanyvariablesthatcanonlybecapturedinastatisticalsense,e.g.,chemicalcomposition,defectdensityanddistribution,texture,grainsize,etc.Ourpremiseisthattheseintrinsicpropertiesandtheirlinkingacrossscalesdetermineamaterial’sproperties(orfunctionality)anditsperformance.Todevelopcontrol,weneedtoestablishthecorrespondencebetweena3Ddescriptionofamaterialanditsproperties,fromwhichwemaydevelopasetofprinciplesthatprovideanintelligentsystemfortailoringmaterialsfunctionality.Tomakeprogressinlinkingbehaviorofmaterialstotheirprocessedcharacteristics,wemustdevelopandmaintaintheintimatecouplingofexperimentwiththeoryandsimulation.

Inotherwords,todevelop“process‐aware”modelslinkingmaterialsbehaviorwithits3Dcharacteristics,werequiretoolsthatseektocoupleandlinkthespectrumofmaterialslengthscales—fromtheelectronicthroughthecontinuumandtotheapplicationorintegratedsystemlevel.Infact,alonghistoryofsuccessfulmodelspunctuatesthelineageofmaterialsscienceinthisquest.Somemodels,suchasopticaldevicetheory,relyonfundamentalphysics;others,suchastime‐temperatureheat‐treatingcurves,arisefromphenomenology;andmost,suchasphasediagrams,combinetheoryandempiricalobservation.Withinthepastthreedecades,thesubspecialtyofcomputationalmaterialssciencehasstrivedtoprovideadditionalmodelingtoolstothematerialsscientist,rangingfrom(i)fundamental(abinitioelectronicstructureandmoleculardynamics)calculationsattheatomic(usuallysinglecrystal)scale,to(ii)dislocationdynamicsandphasefieldmodelingatmesoscopiclengthscales,atwhichmicrostructuralaspectssuchastextureandinterfacialeffectsbecomeimportant,to(iii)singlecrystalandpolycrystalplasticitymodelsthatdescribe“bulk”materialsbehaviorthatcanbeencapsulatedin(iv)EquationofState(EoS)anddynamicmaterialstrengthmodelssuitableforengineering‐levelsimulations.Ourcomputationalmaterialssciencegoalsaretoenableanintegralandpredictivecapability,notpostdictive,andtoprovidealinkbetweenmaterials,design,manufacturing,andfunctionalitythatwillultimatelyenable“control”ofmaterialfunctionality.

Thispanelattemptedtoenvisionthisfutureresearchpathandelucidatetheadvancesinmulti‐scalemodelingtechniquesandalsotheexperimentalcapabilitiesneededtomeasuretherequiredvalidationdatathatwillberequiredtomeetthisgoal.Theheterogeneityofrealmaterialsandthenon‐equilibriumprocessesunderlyingdynamiccompressionphenomenaaretwokeyaspectsabsentfromcurrentmodelsbaseduponadescriptionofaveragehomogeneous,equilibriumbehavior.Apropertreatmentofsuchaspectswillenable

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predictionsofaprobabilisticbulkperformanceratherthanjusttheidealmacroscopicbehavior.Theultimategoalistodevelopthescientificunderstandingthatwillenableatailored“control”ofthechemicalandspatialstructureofmaterialstobetoleranttoextremeenvironments,replacingtheconventionaltrial‐and‐errorapproach.

3.4 Scientific Discovery Challenges for Compression Science Theory and Modeling

3.4.1 Track dynamic microstructure evolution in situ Theresponseofmaterialstodynamiccompressioninvolvesawiderangeoflengthscales,rangingfromindividualpoint,line(i.e.,dislocation),orsurfacedefectsatthenanometerlengthscale,tothenucleationandgrowthofvoids,twins,orproductphasesattenstohundredsofnm,collectivedislocationmicrostructureatmicronlengthscales,andfinallythe10–100µmgrainscale.Currentcomputationalmaterialssciencetechniqueshavebeendevelopedforeachoftheselength(andcorrespondingtime)scales,butacorrespondingsetofdirectinsituexperimentalprobeshasnotyetbeendeveloped.Thisleadstotwochoicesfordesignandparameterizationofthehigherlength‐scalemodels:eitherpostdictivefittingoftheendstateofhighlyintegratedexperiments(e.g.,Taylorcylinderimpactsorrecoveredincipientspallsamples)oran“upscaling”ofdynamicmaterialpropertiesfromonemethodtothenext.Thelatterremainsanextremelychallengingtaskandintroducesatypicallyun‐quantified(butpotentiallyquantifiable)errorfromonesteptothenext(abinitioelectronicstructure,tosemi‐empiricalpotentialsforMDsimulations,tomesoscaleandfinallycontinuum‐scalemodels).Thus,thereisanenormousbenefittodirectinsitumeasurementsofthedynamicmicrostructureevolutionatthemesoscale,whichliesinthegapbetweenthemicroscalewheretheoryismostreliableandthemacroscalewhereexperimentalmeasurementsaremostreadilymade.Twoofthemostpromisingcandidatesinthisregardarethefollowing:

• X‐rayscattering,whichissensitivetomicroscopicdefectssuchasvoidsanddislocations.Anoutstandingchallengeisthe“inverseproblem”ofinferringsuchdefectcontentfromexperiment.

• Microprobesonsynchrotronlightsourceshavereachedalevelofmaturitywherethe3Dmicrostructureofavolumecontainingtensofgrainscanbemappedwithinanhourofbeamtime.Thegrandchallengeistodosuchmeasurementsinsituduringstaticcompressionandultimatelyduringdynamiccompression.

3.4.2 Discover new and unexpected high-pressure and temperature solid phases Thehigh‐(P,T)equilibriumphasediagramsofelementalmaterialsareinmanycasesstillpoorlymappedout,andthesituationisevenworseforalloysandcompounds.Thediscoveryofthehcpεphaseofironbydynamicshockexperiments,onlysubsequentlyconfirmedbystaticexperimentsandtheory,isalandmarkachievementthatgreatlyenhancedthestatureofthatcommunity.Theaccuracyandpredictivecapabilityofabinitioandmoleculardynamicshasreachedastatewherethatcommunityshouldstrivetoseeksuchadiscovery,byexploringthevastregionsofphasespacewhichliebetweentheprincipalHugoniot,isentrope,andisothermsthatdynamicandstaticexperimentshavealreadyaccessed.ThequestionofthestructureofironatEarth’scoreandrelatedplanetary

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scienceissuesarebeingactivelyexploredbytheseapproaches,butotherwisethisisalargelyuntappedareaprimefordiscovery.

3.4.3 Design novel experiments to isolate key physics Todate,thevastmajorityofsimulationshasbynecessitysimplifiedthematerialdescriptionbut,asaresult,hasneglectedthematerialcomplexitythatoftendominatesbehaviorunderextremeconditions.Thephysicsthatarerelevantforunderstandingthestateofmatteratextremeconditionsincludecomposition,phase,crystalstructureandstability,elasticmoduli,andlocalstressoftheperfectcrystal.Inaddition,realmaterialsarecomposedofacollectionofcrystallinegrainswithvariousorientations,shapes,andinternaldefectsthatplayadominantroleindeterminingthematerialbehavior.Suchmaterialcomplexityincludesinternalvacancies,impurities,alloyelements,dislocations,inclusions,secondphaseparticles,andgrainboundaryorotherinterfaces.Assimulationandexperimentalscalesareapproachingeachother,itiscrucialthatsuchcomplexitybeincorporatedinsimulations.

Tobridgethisgapbetweentheoftenidealizedtheoryandsimulationsandtheexperimentsusingofteninsufficientlycharacterizedengineeringmaterials,thereisaneedfornovelexperimentsinvolvingsampleswithcontrolled(oratleastadequatelycharacterized)grainanddefectstructures.Simulationscanthusbeperformedonidenticalsamples(statisticallyifnotexactly),andexperimentscanbeperformedwithinternalmeasurementsofstrainrate,temperature,andstressstatethatdirectlycorrelatetosimulationobservables.

3.4.4 Move beyond planar impact: Non-uniaxial strain experiments Uniaxialandhydrostaticloadingconditionshavebeenmoststudiedprimarilybecausetheyarethemosteasilyachievedinexperiments,andmodeled,butrepresentonlyaverylimitedsubsetofstressandstraintensorstatesthatareaccessedincomplexintegratedexperiments.Experimentsinvolvingobliqueimpact,sweepingwaves,bulgetests,etc.,havebeenperformedandmodeled,butfurtherworkisneededtounderstandthedynamicmaterialresponsetothesemorecomplexloadingconditionsandtoenhanceourconfidenceindynamicmaterialmodelsandcodesundertheentirerangeofstressandstrainstatesatwhichtheyareutilized.

3.4.5 Design novel simulations to isolate key physical mechanisms and observables Thebehaviorofmaterialfollowingachangeinexternalconditionsisdeterminedbythedefectsinsidethematerials.Bydesigningsimulationsthatdirectlymodelthesekeyunitprocesses,simulationswillmakeabetterconnectiontotheexperimentalobservables.Today’shigh‐performancecomputingplatformsenablethedirectmodeling,atanatomisticlevel,ofmaterialsstartingfromanexperimentallycharacterizeddislocationmicrostructure.Adirectnumericalsimulationoftheshockcompressionofmaterialattheatomisticlevelrevealsthedeformationbydislocationmechanisms,whichmaybedirectlyobservedwithexperimentviadiffuseX‐rayscattering.

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3.4.6 Develop ability to predict the kinetics of phase transitions (solid-solid, solid-liquid, and liquid-solid) Materialsexistinmanystates,andthekineticsoftransformationbetweensuchstatesispoorlyunderstood.Todate,heuristicmodelshavebeenfittomacroscopicexperimentalmeasurements,suchasVelocityInterferometerSystemfromAnyReflector(VISAR)waveprofilerecords,butprovidenoinsightintothetransitionmechanisms.Directnumericalsimulationoftransformationsprovidesinsightintothenucleationandgrowthoftheproductphaseandcaninformphysicallybasedmodels.Forinstance,theKolmogorovcontinuummodelrequiresnucleationrates,lagtimes,interfacevelocities,andotherfundamentalparametersthatcanbedirectlydeterminedfromsimulationsatlowerlengthscales,includingmoleculardynamicsandphasefieldsimulations.However,theselowerlengthscalemodelshaveneverbeenvalidatedatextremeconditionsbyexperiment.Insitusmall‐anglescatteringexperimentsrevealthedistributionofnucleiatagivenpointintime;suchdistributionsatmultipletimescanprovideinformationonthekinetics.

3.4.7 Understand relationship between microstructure and constitutive properties (e.g., strength) during dynamic processes Thedynamicbehaviorofamaterialdependsuponitsconstitution,whichincludesphase,microstructure,andloadingpathandrate.Thedevelopmentofapredictivematerialmodelforthatresponserequirestheknowledgeofthemicrostructureevolutionalongtheloadingpathatthegivenloadingrate.Inparticular,strengthisprimarilydeterminedbydislocationunitmechanisms.Thedislocationcontentchangesduringdeformation,andtherateofchangeislargelyunknown.Phenomenologicalstrainhardeningmodelsaccountforthiseffectinamacroscopicwaybutdonotrepresenttheunderlyingmicroscopicphysics.Mesoscaledislocationdynamicsmodelscanaccountforthismicroscopicphysics;howeverthesemodelsneedtobeextendedtoincludedeformation,polycrystals,crystalrotation,andexperimentalinformationondislocationmobilitiesunderextremeconditions.Atomisticmoleculardynamicssimulationscanalsoprovideinformationonthemobilityofdislocationsatextremeconditions,includingconditionsinthepresenceofotherdefectssuchasvacancies,impurities,otherdislocations,inclusions,orgrainboundaries.Thismicroscopicevolutionofthedislocationmicrostructuremustbecapturedinacontinuumratemodel.Thevalidationofthismicrostructureevolutionisessentialandcanonlycomefromemerginginsitu,realtime,X‐ray,neutron,and/orprotonprobeswithhighspatialandtemporalresolution.

Nothingisknownaboutthemicroscopicstateofthematerialfollowingaphasetransition,forinstancethedislocationdensityorgrain(andsubgrain)structure.Thehistorydependenceofamaterialelement,followingitsevolutionthroughphasetransitions,canstronglyaffectitsresultingstrengthandotherdynamicpropertiesinanas‐yetpoorlyknownmanner,whichneedsfurtherinvestigation.

3.4.8 Understand material failure Materialfailureundershockcompressionmayresultfromthelocalizationofdeformationandduringreleasethenucleation,growth,andcoalescenceofmicroscopicvoidsorfracturesmayleadtoductileorbrittlefailure,respectively.Heuristicmodelsomitsuchphysics,forinstance,byassumingthatmaterialfailureoccursataspecifiedmaximumcompression(or

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tensilestress)ηmin(orPmin).Nucleationandgrowthmodelshavebeendevelopedforanumberofotherphysicalsituationsbuthavenotbeenwidelyappliedtomaterialfailuretodate.Directnumericalsimulationsofmaterialfailureundershockcompressioncanrevealtheevolvingporousstateofthematerialunderloadandtheunderlyingphysicalprocesses.Forexample,mesoscalecrystalplasticitymodelswithanexplicitrepresentationofnucleationsites,informedbyatomisticsimulationsofthenucleationandgrowthprocesses,canbedeveloped.Dynamicinsituradiographicimaging,andeventually3Dtomography,canprovidedetailsofthevoidgrowthprocessneededtovalidatethemodels,overcomingthelimitationsofexistingpost‐recoveryanalysisofincipientlyspalledsamples.

3.4.9 Resolve melting discrepancy in transition metals Despiteseveralrecentattemptsinvolvingnewtheoreticalcalculationsandstatichigh‐pressureexperiments,thecompressionsciencecommunityhasfailedtoresolveaglaringdiscrepancybetweenthehigh‐pressuremeltcurvesinseveralbodycenteredcubic(bcc)transitionmetals,mostnotablyMoandTa.Whereasstatichigh‐pressurediamondanvilcell(DAC)experimentsusinglaserheatingrevealaverygradualriseinmeltingtemperature(afewhundreddegreesK)athighpressures,dynamicshockexperimentsandquantummoleculardynamics(QMD)simulationsbothpredictamuchsteepermeltcurve,risingthousandsofdegreeswithremarkablygoodagreementbetweenthedynamicexperimentsandtheory.ThefactthatseveralgroupsinboththeUnitedStatesandEuropehavedemonstratedthereproducibilityofmanyofthesecalculationsandexperimentsmakesthisdiscrepancyevenmoreintriguingandsuggestsanoverlookedexplanationthatmaypotentiallyraisequestionsaboutawiderrangeofexperimentsorcalculations.Forinstance,ontheonehand,theassumptionofahydrostaticstressstateandthermalequilibriuminDACexperiments,andneglectofelectrontemperatureinvirtuallyallQMDandMDcalculations,evenastemperaturesapproach1eV,couldintroducesignificanterrors.Ontheotherhand,staticanddynamicexperimentsareinexcellentagreementwitheachother(andwiththeory)fornon‐transitionmetals,includingAl,Fe,Mg,andNi,whichcouldsuggestthatanintermediatesemi‐orderedphaseakintoaliquidcrystalmaybeaprecursortomeltingforbcctransitionmetals,confoundingtheinterpretationofwhatmeltingactuallyis.

3.4.10 Understand the behavior of the full anisotropic stress state at extreme pressures and temperatures, e.g., Poisson’s ratio approaching melt Relatedtothepreviouschallenge,materialpropertiessuchasPoisson’sratioandstrengthapproachingmeltarestillpoorlyunderstood.Theexistenceofnewphases,ordrasticchangesinbehaviorofexistingphasesnearmelting,couldaffecttheinterpretationofexperimentsandprovideinsightintovarioustheoriesofmelting,fromBorn’sproposedelasticinstabilitytomoremoderntheoriesofdislocation‐mediatedmelting.

3.5 Technical Grand Challenges for Compression Science Theory and Modeling

3.5.1 Multiscale modeling free of ad hoc parameters: linking subscale processes to higher length/time scales Thefieldofmulti‐scalemodelingtodaycontainsseveraltheoreticalandcomputationaltools,whichtogetherspanthetimeandlengthscalerangesofinteresttostaticanddynamic

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compressionscience.Eachmodelingtool,ingeneral,containsbothphysicallybasedandnon‐physicalquantities(parameters)thatallowtherepresentationofmaterialresponse.Thenon‐physicalquantitiesexistduetoourlackofunderstandingabouteitherthephysicalprocessesthatoccurinrealmaterialsorhowtorepresentknownphysicsintoatheoryorcomputationaltooladequately.Ourlackofexperimentalinformationaboutdynamicresponsesandstructuralevolutionofmaterialsatlengthscalesofimportancetothephysicalprocessespreventsusfromdevelopingthetheoreticalandcomputationaltoolstoadequatelyachievepredictivemodelsattherelevantlengthscalesforourproblemsofinterest.

Theinformationdeficitcanbeaddressedthroughhigh‐fidelitydiagnosticsappliedtocriticalexperiments.Eliminatingnon‐physicalparametersfromtoday’smodelsisthegoalatalllengthscales.

3.5.2 Better theoretical tools in the mesoscale (1–10 mm) regime Themechanicsandphysicscommunityhasovermanyyearscollectivelyproducedtheoreticaltoolsthathavestartedatthecontinuumlevelandworkeddowninlengthscaleorattheatomicscaleandworkedupinlengthscale.Althoughthesecontinuingeffortsarecritical,wedonothaveadequatetheoreticaltoolsthatdescribethecomplexwaysinwhichdislocationsinteractandformsubstructuresorhowtheyinteractwithmicrostructuralfeaturessuchasinclusions,grainboundaries,pointdefects,precipitates,dislocationsources,etc.Presentpolycrystalplasticitymodelshavedemonstratedourdeficiencyindescribingthedevelopmentandevolutionofsubgrainheterogeneitiesandstructure.

Thesetheoriesmustalsorepresentrealmateriallengthscalesintheirformulationinordertoeliminatemanyofthesedeficienciesandprovidemicrostructuralsizedependence,whichisknowntoexistinallmaterials.Atpresent,crudetheoriesattempttorepresentrealmateriallengthscales,butthesetheoriesareverycomplex,lessthanphysicallybased,andcomputationallyexpensive.Wemustdriveourunderstandingtothepointatwhichwecanrepresenttheselengthscaledependentbehaviorswithphysicallybasedmodelsthatareassimpleaspracticallypossibleandincludesufficientinformationtolinkacrossthelengthscales,whichthatparticularmodeldivides.

3.5.3 Transferable density functionals, pseudopotentials, and classical MD potentials valid at extreme conditions Presentdayinteratomicpotentialsarelimitedtotheregimesofresponsewithinwhichtheywerecalibrated.Thislimitationpreventstranslationtoawidersetofphysicalregimes,whichthuslimitspredictivecapability.Wemustdevelopnewcomputationalframeworksthatenableawiderrangeofknowninteratomicinteractionstoallowrepresentationofthedetailedcomplexitiesofrealmaterials,whichinherentlycontaindefectsandareexposedtoextremeenvironmentalconditionsofloading.Particularlyfordynamiccompressionexperimentsthataccessextremepressureandtemperaturestates,thereisaneedforfurtherresearchintotwotechniquesthatpromisetocorrectpotentiallyfatalweaknessesincurrentdensityfunctionaltheory(DFT)andMDcalculations:temperature‐dependentdensityfunctionalsandclassicalpotentialsforMDsimulationsthatareelectrontemperature‐dependent.

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3.5.4 Equation of state treatment of materials beyond simply pressure and volume

• Avoidrelianceonsimpleseparationintohydrostaticanddeviatoricstresses

• Two‐temperature(electronandion)EoS’s

Presentdaytheoriesarebuiltuponthesimplificationofdecouplingtheeffectsonmaterialsofthehydrostatic(pressure)anddeviatoric(shear)partitionsofstress.Inreality,theequationofstateforanycrystalstructure(exceptacubicatreferenceconfiguration)compressesthroughapplicationofhydrostaticpressurebychangingbothvolumeandshape.Theoriesusedtodaydonotaccountfortheeffectoftheshearresponseduringhydrostaticcompression.Theoriesaccountingforthiscouplingatpresentlacksufficientexperimentalinformationtoenabletheircompletedevelopmentanduse.Thelackofcouplingbetweenpressureandshearpreventsanadequatetreatmentofpressuredependentplasticityandcalculationofthermodynamics.AdditionaldatafrombothexperimentsandsimulationscanbeusedtocalibratemorecompleteEoSformulations.

CurrentEoSframeworksassumetheBorn‐Oppenheimerapproximationthatelectroncontributiontothethermodynamicsstatevariablesisnegligible.Thisforcestheassumptionoflocalthermodynamicequilibrium(LTE)atallconditions.ItiscurrentlybelievedthatLTEdoesnotexistunderstrongshockconditionsandinwarmdensematter.Extendingformulationstotwotemperatures(electronandion)isafirststeptowardprovidingabettertreatmentfornon‐LTEconditions.

3.5.5 Codes that preserve the integrity of material models Currentnumericalframeworksdonothandlesteepgradientsinloadingandmaterialstateadequately.Thisdiffusesfields,preventingtheadequatetreatmentofsurfaces(eithermaterialvariablesorinterfaces).Manyofthesesteepgradientsarebelowtheresolutionofthecomputationalgrid.Numericalschemesarerequiredtomoreadequatelyrepresentsteepgradientsand/ortrackmaterialstatewithoutdiffusion.

3.5.6 Quantitative dynamic x-ray probes (diffraction, XANES, EXAFS, etc.) • Insitudeterminationofphase

• Measurevolumefractionofgrowingproductphase

Toacquirenecessaryexperimentalinformationatlengthscalesthatarenotpresentlyachievable,newdiagnosticprobeswillberequired.Ingeneral,diffractiontechniquesareusedtodistinguishmaterialphaseinformationinavolumeaveragedfashion.Diffusescatteringisimpactedbytheexistenceandevolutionofdisorderinwhichthematerialscanbeboththermalandstructural.Ofparticularinterestisthespatialdistributionofdislocationsandtheevolutionofdislocationdensitywithdeformation,whichiscrucialinunderstandingtheevolutionofstrength.Small‐anglex‐rayscatteringissensitivetothepresenceofdensityheterogeneityinthematerials,andthesematerialsincludeprecipitates,voids,secondphaseparticles,andphasenuclei.Bothdiffractionandsmallanglescatteringcanbeusedtodeterminethegrowingvolumefractionofphase.

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TheXANESandEXAFStechniquesprobetheelectronicstateoftheatomandaresensitivetothelocalenvironmentsurroundingtheatom,includingnearestneighborspacing,stress,andtemperature.Thesetechniquesornewtechniquesmustbedevelopedtoenablethemeasurementofthenucleationofthesephasechangeseventsatverysmalltimeandlengthscales.Inaddition,newvisualizationanddataprocessingtoolswillbenecessarytodealwiththelargedatasetsproducedfromthethree‐dimensionalmeasurements.

3.5.7 Develop local temperature and stress tensor gauges Presenttemperatureprobesarelimitedtothesurfaceofthesampleorareinvasiveandhavethepotentialtoinfluencetheresultsbytheirexistence(e.g.,thermocouples).Surfaceprobesarebasedupontheemissivityofthesample,andtheoriesdescribingemissivityasafunctionoftemperatureareinadequateforthebasingmeasurementuponemissivity.Temperatureisafundamentalquantityindeterminingthethermodynamicstateofthematerialandintheinfluencethatthethermalstatehasontheconstitutiveresponseofthematerial.Wemustdevelopthetoolstoenablethemeasurementofinsitutemperatureinadeformingbodyatlengthandtimescalesthatareconsistentwithpresentmodelingtools(e.g.,1micronand1ns).Advancementsofphotoniccrystalsthatcouldbeembeddedintoamaterialsandimagesproducedwitharadiationsourcecouldholdpotentialforattainingarealthree‐dimensionaltemperaturefield.

Aswehavediscussedearlier,wemustbegintoaccountforthecomplexthree‐dimensionalstressstateinboththetreatmentofEoSandstrengththeories.Todothis,wemustdeveloptechniquestomakeinsitumeasurementsofthefullstresstensorfieldinmaterialsasafunctionofposition.Thiswillallowustomorecompletelyevaluatethelocalconstitutivebehaviorofmaterials.Measurementofonlythedeformationfieldwillstillrequireustoestimatethroughmodelingthekineticresponseofthematerial.Manganingaugesarepresentlyusedandarelimitedtofinitevolumesandareusedfortractiononly—noshear.Thepaneldidnotoffergoodsuggestionsfortechnologiesthatmightshowpromiseinmakingthesemeasurementsinsituandatasmalllengthscale.

3.5.8 Local structural identification in static experiments, e.g., DAC, for amorphous materials and liquids Statichigh‐compressionexperimentaltechniquesdowellforcrystallinesolidmaterials–particularlydiffractiontechniques.Thesamediagnosticcapabilitiesdonotexistforotherclassesofmaterialssuchasamorphoussolidsandliquids,yettheirbehaviorisnotwellcharacterized.Wemustdevelopthediagnostictechniquestoenablethemeasurementoflocalscalestrain,stress,structureformaterialsthatlackcrystallinityorareatleastonlypartlycrystalline.

3.5.9 3D orientation image mapping to dislocation length scales under dynamic conditions Theresponseofmetallicmaterialstoexternallyimposedloadingisnotsimplyafunctionofthetypesofelementalmaterialsexistinginthematerials.Theirresponseisalsoafunctionofthespatialpositioneachofthoseelementalmaterialshasinthebulkmaterial.Imperfectionsanddefects(e.g.,grainboundaries,dislocations,impurityinclusions)alsoplayamajorroleindeterminingthedeformationbehaviorofmetallicmaterials.Thespatialarrangementofatomsanddefectsinthematerialcomprisewhatiscommonlytermedasthematerial

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microstructure.Themicrostructurealsoevolvessubstantiallywithdeformation(distortion,dislocationmovement/evolution/arrangement,heterogeneityevolution)andwhenconditionsareextreme,thisevolutionleadstomaterialdamageandfailure.Theseareunsolvedproblemsfromatheoreticalperspective.Wesimplyarenotyetabletomodelthesecomplexprocessesinapredictivemanner.Weneedtobeabletomeasuretheevolutionofthemicrostructureduringdynamicloadingconditionstoenableustomakeinsituobservationsofhowmicrostructuralheterogeneitiesevolveandleadtodamageandfailure.OrientationImageMapping(OIM)isawell‐known2Dtechnique,whichispresentlyusedtocharacterizethecrystallographicorientationofpolycrystallinemetallicmaterials.Coupledwithlaboriousmechanicalserialsectioning,itcanpresentlybeusedasawaytocharacterizethe3Dmicrostructureofamaterialforasamplerecoveredfromamechanicaldeformationhistory.This2Dtechniqueteachesusagreatdealaboutthebehaviorofamaterialbutonlyin2Dandafterthefact.Togettothenextlevelofunderstanding,weneedhaveatoolwhichwilltellusinformationlikeOIMisabletonowbutin3Dandduringdynamicloadingresponses.

3.5.10 Extracting useful information from high-resolution 3D data (e.g., from 3D tomography or large-scale simulations) Asourabilitytoproduceverylargeexperimentalorcomputationaldatasetsbecomesgreater,sotooistheneedtobeabletoextractusefulphysicsinformationfromthoselargedatasets.Aswebegintothinkabouthowmaterialmicrostructuresevolvetoproduceanobservedbehaviororaswebegintobeabletousenewphysicsunderstandingtoenableustoproducematerialmicrostructuresthattakeadvantageofinherentheterogeneitiestoouradvantage,itwillbeincreasinglyimportanttomakethelinkingbetweendifferentphysicsevents.Forexample,wemaywishtoderiveanevolving3Dvelocity,strain,orstrainratefield,byperformingimagecorrelationsfor100time‐sequenced3Dmicrostructuralimagestothelevelofresolutionoftheimages.Thiswillrequirecharacterizingeachimage(OIMtypeinformation)butalsolinkingeachimagetothenextimageornextfewimagestobeabletoproposeanevolvingfield.Thesamecanbesaidfortheanalysisoflarge‐scaleMDcalculations.Muchinformationisproducedduringthosesimulationsandthecorrelationsofeachatomwithitsnearestneighborswilldefinealatticestrainfieldbutalsomayhelptodefineanewsolidphasedependinguponthelocalstructure.Theanalysesperformedwillgenerallyhaveabasisinaparticularphysicsquestion,whichwemaywishtoaddress.Manyoftheprocesseswehavediscussedherehavebeenaroundtheconceptofevolvingstatistics.Wewillalsoneedhigherorderstatisticalmodelstobeabletotractablycapturethestatisticsofmaterialbehaviorintosomethingwhichwecanusetohelpuslinktheevolutionofheterogeneitiestoobservedordesignedproperties.WecanalsousethesestatisticalmodelstohelpdefineinitialconditionmicrostructuresforMD,phasefield,andpolycrystalmodelsthatrepresentrealmaterialsofinterest,whichwillalwaysbeginataninitialstateofheterogeneity(defectstructure).

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4.0 Conclusions Theworkshopofferedanopportunityforopendiscussionoftheproblemsandchallengesinthefieldofcompressionscience.Theseproblemsandchallengespresentopportunitiesforadvancingourfieldandmovingthefieldfromthatofdiscoveryandobservationtothatofpredictionandcontrol.Thistransitionrequiresthatwediagnoseanddevelopanunderstandingofmaterials,notinanidealsenseoftheoryalone,butalsoinareal‐worldsenseofexperimentandmeasurement.Tomakeprogressonthesehigh‐levelgoalsrequiresthecommunitytomeetasetofchallengesthatincludethefollowing:

• Acquiretimeandspatiallyresolvedinsitumeasurementsatalllengthscales(i.e.,atomistic,micro,meso).

• Discovernewphysicsandchemistryinextremeenvironments.• Incorporatematerialcomplexityintomulti‐scalesimulationstoachievepredictive

capability.• Unifystaticanddynamiccompressionunderstandingacrossrelevantlengthandtime

scales.• Leveragescientificknowledgederivedfromtheoryandexperimenttothedesignand

controlofrealmaterials(i.e.,chemistry,microstructure,defects,etc.)

Furthermore,wehaveidentifieddetailedchallengesandopportunitieswithintheframeworkofstatic,dynamic,andtheoreticalcompressionsciencethatworktowardattainingourendgoalofcontrol.Resolvingallofthesechallengesisnecessaryfortruepredictiveunderstanding,whilepartialresolutionwillleadtonewparadigmsregardingourthoughtprocessesonthematerialworldaroundus.Compressionscienceoffersopportunitiesfordiscovery,yetchallengesourabilitytofullycomprehendthecontrollingchemistryandphysics.Asscientists,werecognizethecomplexityandacknowledgetheunderlyingbeautyinthefieldofcompressionscience,andwelookforwardtothesurprisestocomeandtheexpectedsuccessofourpredictivecapability.

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Appendix I Workshop Agenda 21stCenturyNeedsandChallengesinCompressionScienceWorkshop

Bishop’sLodge,SantaFeNMTuesday,September22,2009

7:00PMDinner TesuqueA,B

Ifyouareavailable,weareexpectingaspeakeronTuesday,September22,2009

(unfortunately,notconfirmed):8:00PM

Wednesday,September23,2009TesuqueA,B

8:00–8:30AMContinentalBreakfast TesuquePavilion8:30AMWelcome,IntroductionandWorkshopKickoff………DavidFunkandRustyGray LosAlamosNationalLaboratory 9:00AMTheFutureofStaticCompressionScience…………...…………MalcolmMcMahon UniversityofEdinburgh10:00AMDiscussion10:30AMTheFutureofDynamicCompressionScience………………………YogiGupta

WashingtonStateUniversity11:30AMDiscussion12:00PMLunch–WorkshopCo‐chairwillleaddiscussiononthemorningPlenaryTalksTesuquePavilion

TesuqueA,B1:00PMExperimentalNeedsforMaterialPhase,Strength,andDamage…….NeilBourneAtomicWeaponsEstablishment JamesAsay SandiaNationalLaboratories

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2:00PMDiscussion 2:30PMBreak

3:00PMTheoryNeedsforMaterialPhase,Strength,andDamage………………JamesBelak LawrenceLivermoreNationalLaboratory CurtBronkhorst LosAlamosNationalLaboratory

4:00PMDiscussion4:30­5:30PMSummaryDiscussion

6:00PMReception/InformalDiscussionTesuquePavilionC7:00PMDinner–WorkshopCo‐chairwillleaddiscussionfrombreakoutdiscussions(using

keyquestionstostimulatediscussion)TesuquePavilionC

Thursday,September24,2009­­BreakoutSessions

LasFuentesAlcoveRoom—FutureofStaticCompressionScienceLasFuentesFiestaRoom—FutureofDynamicCompressionScienceTesuquePavilionC—TheoreticalNeedsofCompressionScience

8:00–8:30AMContinentalBreakfast TesuquePavilion8:30AMRetiretosideroomsforindependentdiscussionandpresentationofeach

participant’smaterials(tenminutesperparticipant) 12:00PMLunch–PanelChairswillreportbackontheprogressfromthemorningsessions;andthatprogresswillbeusedbyallintheafternoonbreakoutsessionsTesuquePavilion2:00­4:00PMPanelsdevelopsummarypresentations(5slides)

TesuquePavilionA

4:00PMPanelChairspresentsummaries(20minuteseach)5:00­6:00PMSummaryDiscussion6:30PMInformalDiscussion/ReceptionTesuqueA,B7:30PMDinner–PanelChair/Co‐chairwillleaddiscussiontorefineworkshopinformationpresentedintheafternoonsessionTesuqueA,B

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Friday,September25,2009­­ReportWriting

8:00–8:30AMContinentalBreakfast TesuquePavilionPortal

TesuquePavilionC

8:30AMPanelChairsandPlenarySpeakersdraftreports(5‐7pagesfromeach)12:00PMWorkshopAdjourns

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Appendix II Participants 21st Century Needs and Challenges in

Compression Science Workshop

JamesAsay

SandiaNationalLaboratoryE‐mail:jrasay@sandia.gov

CrisBarnes LosAlamosNationalLaboratoryE‐mail:cbarnes@lanl.gov

RichardBecker LawrenceLivermoreNationalLaboratoryE‐mail:becker@llnl.gov

JamesBelak LawrenceLivermoreNationalLaboratoryE‐mail:belak1@llnl.gov

ReinhardBoehler CarnegieInstitutionofWashingtonE‐mail:rboehler@ciw.edu

NeilBourne AtomicWeaponsEstablishmentE‐mail:neil.bourne@mac.com

CurtBronkhorst LosAlamosNationalLaboratoryE‐mail:cabronk@lanl.gov

MichaelDesjarlais SandiaNationalLaboratoriesE‐Mail:mpdesja@sandia.gov

MichelineDevaurs LosAlamosNationalLaboratoryE‐mail:devaurs_micheline@lanl.gov

DanaDlott UniversityofIllinoisEmail:dlott@illinois.edu

JonEggert LawrenceLivermoreNationalLaboratoryE‐mail:eggert1@llnl.gov

WilliamEvans LawrenceLivermoreNationalLaboratoryE‐mail:wjevans@llnl.gov

DavidFunk LosAlamosNationalLaboratoryE‐mail:djf@lanl.gov

TimothyGermann LosAlamosNationalLaboratoryE‐mail:tcg@lanl.gov

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George“Rusty”Gray LosAlamosNationalLaboratoryE‐mail:rusty@lanl.gov

Yogendra“Yogi”Gupta WashingtonStateUniversityE‐mail:ymgupta@wsu.edu

RusselHemley CarnegieInstitutionofWashingtonE‐mail:larson@lanl.gov

JohnKlepis LawrenceLivermoreNationalLaboratoryE‐mail:klepeis1@llnl.gov

MarcusKnudson SandiaNationalLaboratoriesE‐mail:mdknuds@sandia.gov

ChristianMailhiot LawrenceLivermoreNationalLaboratoryE‐mail:mailhiot1@llnl.gov

H.K.DaveMao CarnegieInstitutionofWashingtonE‐mail:Mao@gl.ciw.edu

RickMartineau LosAlamosNationalLaboratoryE‐mail:rickm@lanl.gov

StephaneMazevet

UniversiteDeBrtagneOccidentE‐mail:stephane.mazevet@cea.fr

MalcolmMcMahon

UniversityofEdinburghE‐mail:mim@ph.ed.ac.uk

JohnMoriarty

LawrenceLivermoreNationalLaboratoryE‐mail:moriarty2@llnl.gov

NigelPark

AtomicWeaponsEstablishmentE‐mail:nigel.park@awe.co.uk

MichaelPravica UniversityofLasVegasE‐mail:pravica@physics.unlv.edu

PauloRigg LosAlamosNationalLaboratoryE‐mail:prigg@lanl.gov

AdamSchwartz LawrenceLivermoreNationalLaboratoryE‐mail:schwartz6@llnl.gov

D.ScottStewart

UniversityofIllinoisE‐mail:dss@illinois.edu

SarahStewart‐Mukhopadhyay

HarvardUniversityE‐mail:sstewart@eps.harvard.edu

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JustinWark OxfordUniversityE‐mail:justin.wark@physics.ox.ac.uk

PhilWithers

UniversityofManchesterE‐mail:philip.withers@manchester.ac.uk

SashaZivaljevic LosAlamosNationalLaboratoryE‐mail:sashaz@lanl.gov

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Appendix III Cross-cutting issues identified during the workshop

Althoughmaterialsunderextremeenvironmentsofpressure,temperature,andstrainratearecentraltodefense,energy,andothertechnologies,weknowrelativelylittleabouthowandwhymaterialsrespondundertheseconditions.Tounderstandtheoperativecontrollingmechanismsandlearntodesignandcontroltheeffectsofextremeenvironmentsonmaterials,wemustdevelopinsituexperimentsthatseethedynamicsinrealtime.Suchexperimentsarecomingwithinreach,aseverbrightersourcesofelectrons,x‐rays,andneutronswitheverhigherspatialandtemporalresolutionallowsensitivemeasurementsoneversmallersectionsofmaterials.

Asecondreasonforourlimitedknowledgeofmaterialsunderextremeenvironmentsofstaticanddynamiccompressionistheenormouscomplexityoftheeffectssuchenvironmentscause.Unravelingtheemergentbehaviorofmaterialsunderextremeenvironmentsrequiresmorethanobservingtheresponseofthematerialinsitu.Wemustunderstandandmodelthisbehaviortoseehowextremeenvironmentsdamage,degrade,andultimatelydisablematerials.Oneofthemostpervasiveanddifficultchallengesblockingthisunderstandingisthediverserangeoftimeandlengthscalesthatgoverncompressionbehavior.

Discussionoftheworkshopattendeesfollowingtheoverviewpresentationsledtotheidentificationofanumberofcross‐cuttingthemesofrelevancetostaticcompression,dynamiccompression,andtheoryasfollows:

• HowdowebuildconfidencethatclassicalMDprovidesrepresentativeandaccuratephysicsinbothatomicandpolycrystallinesimulations.Arethepotentialsaccurate?Thatis,arethepotentialsaccurateinbothfullydenseanddefectedmaterials?Howdowedevelopasinglesimulationcapabilitythatcancapturealloftherelevantphysicalparameters(i.e.,conductivity,phonondensityofstates,electronicstructure,phasediagram,etc.)?

• Howdowelinkstaticanddynamicresultsparticularlyinthosesituationsinwhichlargediscrepanciesexist?Aretheissueskinetics/calibrationsormisinterpretationofdiagnostics,andhowdoweresolvethisissue.

• Three‐dimensionalimagingofbothsingle‐crystalandpolycrystallinematerialsisneededtodriveourunderstandingofmaterialresponsetocompression.

• Howdoweelucidatelinkagebetweenmicrostructure,defectsandotherheterogeneitieswithconstitutivepropertiesunderloadingconditions;staticordynamic?Canwedrawgeneralinferencesthatwillleadtopredictivecapability?

• Whenislocal‐thermodynamicequilibriumvalidindynamicsystems(includingstatic/lasercouplingexperiments)?Howdoweknowwhenandifwehavereachedequilibrium?

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• Howdowebuildbridgesbetweenlengthandtimescalesthatcapturesandhandsoffrelevantphysics?Canwelookatmultiplescales,bothtemporalandspatial,usingmultiplediagnosticsinasingleexperimentandassessourmulti‐scalesimulationcapabilities?

• Howdowecreateequilibriumconditions/statesofpressureandtemperatureordersofmagnitudegreaterthancurrentlyattainableinrelevantsamplesizes?

• Howdowecharacterizeandquantifythephysicalprocesses(viscosity,localization,instabilities/mixing,phasetransitions,transport,defectgenerationandstorage,damage)inanarbitraryloadingevent?[Geophysicaltolaserdrivenshock]Howdowequantifythepartitioningofenergybetweendissipativeandnon‐dissipativeprocesses?

• Howdowecharacterizeandpotentiallyexploitchemicalchangesthatoccureitherthroughstaticcompressionormaterialdependentchangesinducedbycompression(polymerdecomposition,detonation)?

• Howdoweformulateproblemsofstudysuchthatexperimentslookmoreliketheoryandtheorylooksmorelikeexperiments?Whatarethecriticaltestsoftheorythatprovideconfidenceinourpredictivecapability?

• Howdowecaptureanisotropyinourconstitutiveandequationofstatedescriptionsofrealmaterials?

• Howdowecapturethestochasticnatureofmaterialsaccuratelywithoursimulationcapabilities?Thereafter,howdowevalidatemeso‐scalesimulations?Whatarethenewnumericalschemesthatwillcapturesubscalephysicsaccurately;i.e.,rareevents?