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Nuclear Weapons JournalPO Box 1663Mail Stop A142Los Alamos, NM 87545

Presorted Standard U.S. Postage Paid Albuquerque, NM Permit No. 532

Issue 2 2009 LALP-10-001

Nuclear Weapons Journal highlights ongoing work in the nuclear weapons programs at Los Alamos National Laboratory. NWJ is an unclassified publication funded by the Weapons Programs Directorate.

Managing Editor-Science Writer Margaret Burgess

Editorial Advisor Jonathan Ventura

Send inquiries, comments, subscription requests, or address changes to [email protected] or to the

Nuclear Weapons Journal Los Alamos National Laboratory Mail Stop A142 Los Alamos, NM 87545

Designer-Illustrator Jean Butterworth

Technical Advisor Sieg Shalles

Science Writers Brian Fishbine Octavio Ramos

Printing Coordinator Lupe Archuleta

WEAPONSIssue 2 • 2009

nuclear

journal

Table of Contents

Weapons Programs Performance Snapshot 1Point of View— Strategic Weapons in the 21st Century: Hedging Against Uncertainty 3

Energy Balance in Fusion Hohlraums 6

Upgrades Made to the Trident Laser Facility 12

Fogbank: Lost Knowledge Regained 20The Los Alamos Branch of the Glenn T. Seaborg Institute for Transactinium Science 22

About the cover: Clockwise from left, Ray Gonzales replaces a flash lamp in the laser amplifier at the Trident Laser Facility. Gonzales adjusts a mirror on the front end of the Trident laser. A 5-ft-diameter vacuum vessel in the north target chamber is used for laser-matter interaction experiments. A graduate student, Sandrine Gaillard, checks laser and diagnostic alignment in the north target chamber before a 0.2-PW experiment. Photos: Robb Kramer, ADEPS

The Origin of the Z NumberNWJ Backward Glance

During the Manhattan Project, the US Army Corps of Engineers provided all support

services, including maintenance and utilities, for the laboratory and the townsite. In 1946, President Truman signed the Atomic Energy

Act, which established the Atomic Energy Commis-sion (AEC), a civilian agency. Under the terms of the 1946 act, the AEC was to be the “exclusive owner” of production facilities, but could let contracts to operate those facilities. At midnight on December 31, 1946, Manhattan Project assets transferred to the AEC. In 1947, the AEC began oversight of the Los Alamos Scientific Laboratory and the closed town of Los Alamos.

When the Zia Company was organized in April 1946 to assume support operations for Los Alamos, security was still very tight. Not only were badges required for all office and laboratory workers, but every resident, including children, needed a pass to get through the main gate (formerly a restaurant named Philomena’s and now De Colores on Route 502).

AEC officials decreed that employees of the new Zia Company would be given badge numbers with the

prefix “Z.” Until then, everyone had US Army security credentials. The protective force badge office slipped the letter Z and the number 00001 into its camera and the word went out to the Zia office for employees to report to the badge office and receive a new badge. When US Army numbers were dropped, other Los Alamos residents were given “Z” numbers too.

As the property management agent for the AEC, the Zia Company furnished plumbers and other craftsmen around the clock to repair furnaces, roof leaks, or whatever else might go wrong. Among other services, Zia workers installed clotheslines, planted trees, painted rooms, and changed light bulbs. In 1966, all residences were sold and then Los Alamos residents had to do their own maintenance or call commercial craftsmen.

Los Alamos National Laboratory still assigns Z numbers to employees. A “Z” number is a permanent employee number assigned to only one person. This number identifies the employee throughout his or her career at the Laboratory and is the same number even if the employee should return decades later.

The main gate as it appeared during the Manhattan Project. Inset, the location of the former main gate as it appears today.

1Nuclear Weapons Journal, Issue 2 • 2009

NWJWeapons Programs

Performance Snapshot

Weapons Programs Level 1 and Level 2 Milestones (139)FY09 LANL year-end status

• Totalreportablecases(TRC)—thosethatresultinanyofthefollowing:death,daysawayfromwork,restrictedworkortransfertoanotherjob,ormedicaltreatmentbeyondfirstaidorlossofconsciousness

• Daysawayfromwork,restrictedworkactivity,ortransfer(DART)toanotherjobasaresultofsafetyincidents

complete 121cancelled 6unachievable as stated 6no status provided 6 (FY10 dates)

Level1(L1)milestones—verysubstantive,multiyear,supposedtoinvolvemany,ifnotall,sites

Level2(L2)milestones—supportachievementofL1goals,annual

MilestonesarereportedtoNNSAprogrammanage-mentonaquarterlybasis.ProgressonmilestonesisenteredintotheMilestoneReportingTool.

T hePerformanceSnapshotgivesourexternalcustomersdataonhowtheweaponsprogramsareperforminginthreecriticalareas:Level1andLevel2programmaticmilestones,safety,andsecurity.

Safety Trends April 2009 through September 2009

TRC 12-month cumulative*DART 12-month cumulative*TRC incidents per monthDART incidents per month*per 200,000 productive hours

3.0

2.0

1.0

0.0

Apr-09 May-09 Jun-09 Jul-09 Aug-09 Sep-09

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2 Los Alamos National Laboratory

Security Trends April 2009 through September 2009

Incidentsofsecurityconcern(IOSCs)arecategorizedbasedonDOE’sIMItable(right).TheIMIroughlyreflectsanassessmentofanincident’spotentialtocauseseriousdamagetonational,DOE,orLANLsecurityoperations,resources,orworkersordegradeorplaceatrisksafeguardsandsecurityinterestsoroperations.

Categories of IOSCs (DOE M 470.4-1, Section N)

IMI-1 Actions,inactions,oreventsthatposethemostseriousthreatstonationalsecurityinterestsand/orcriticalDOEassets,createserioussecuritysituations,orcouldresultindeathsintheworkforceorgeneralpublic.

IMI-2 Actions,inactions,oreventsthatposethreatstonationalsecurityinterestsand/orcriticalDOEassetsorthatpotentiallycreatedangeroussituations.

IMI-3 Actions,inactions,oreventsthatposethreatstoDOEsecurityinterestsorthatpotentiallydegradetheoveralleffectivenessofDOE’ssafeguardsandsecurityprotectionprograms.

IMI-4 Actions,inactions,oreventsthatcouldposethreatstoDOEbyadverselyimpactingtheabilityoforganizationstoprotectDOEsafe-guardsandsecurityinterests.

IMI-1 & IMI-2 normalized 12-month cumulative*IMI-3 & IMI-4 normalized 12-month cumulative*IMI-1 & IMI-2 incidents per monthIMI-3 & IMI-4 incidents per month*per 200,000 productive hours

4

3

2

1

0

Apr-09 May-09 Jun-09 Jul-09 Aug-09 Sep-09

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Strategic Weapons in the 21st Century:Hedging Against Uncertainty

Patrice Stevens, Staff Member Los Alamos National Laboratory

NWJPoint

of View

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ATEGIC WEAPON

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RENCE LIVERMORE AND LOS ALAM

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NATIONAL LABORATORIE

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LosAlamosandLawrenceLivermorenationallaboratoriescosponsoredthethirdannual

ConferenceonStrategicWeaponsinthe21stCentury.LaboratorydirectorsDr.MichaelAnastasioandDr.GeorgeMillerhostedtheconference,whichtookplaceJanuary29,2009,inWashington,DC.Theconferencethemewashedgingagainstuncertainty.

TheLaboratory’smissionistodevelopandapplyscienceandtechnologytoensurethesafety,security,andreliabilityoftheUSnucleardeterrent;reduceglobalthreats;andsolveotheremergingnationalsecuritychallenges.ThisconferencesupportstheLANLmissionbyprovidingprogramandpolicyanalysisandenablesinformeddecisionsaboutthestrategicdirectionofournationalsecurityprograms.

USpolicymakersanddefenseexpertsattendedtheconference,includingformerSecretariesofDefenseWilliamJ.PerryandJamesR.Schlesinger.SenatorJeffBingamanofNewMexicoandSenatorJonKylofArizonawerekeynotespeakers.

Why Hedge Against Uncertainty?Thepost-coldwar,post9/11internationalsecurityenvironmentcontinuestoevolvewhilethreatsrisefromthepotentialproliferationofweaponsofmassdestructionandinternationalterrorism.Inthisenvironment,theUSdefenseestablishmentiscurrentlytransformingpolicy(e.g.,theQuadrennialDefenseReview,theNuclearPostureReview,andtheComprehensiveTestBanTreaty),forces,operations,andinfrastructureneededtoassureanddefendalliesanddissuadeadversariesundertheObamaadministration.

Thesupportthatthenationallaboratoriesprovideforongoingstockpilemaintenanceandhedgingagainstuncertaintywaspartofthisyear’sconferencediscussions.Thesediscussionsincludedialogue

pertainingtoanationalsecuritybudgetthatsupportsanuclearweaponscomplexconfiguredforasmallerstockpileandacorrespondingnuclearweaponsdismantlementeffort.

ProgresstowardachievingtheUSgoalofaworldwithoutnuclearweaponscanonlybemadebyverificationandnegotiatedreductionssuchastheStrategicArmsReductionTreaty.TheNuclearPosture

Review,dueinearly2010,willestablishUSnucleardeterrencepolicy,strategy,and

forcepostureforthenext5to10years.

TheObamaadministrationfacesgreateconomicandnationalsecuritychallenges.Thescientificandengineeringchallengeofmaintainingaviabledeterrenthasbeenneglected.

Thissituationisillustratedbythefactthatthenuclearweaponscomplexis

deterioratingandwearelosingexpertiseinnucleardesignandmanufacturing.

Therefore,wefaceincreasinguncertaintyaboutandhaveinsufficientcapacitytorespondtoproblemsrelatedtonationalsecuritythreatssuchasthehedgingstrategiesthatpreserveorprovidetheabilitytowiselyandeffectivelypostureourforcesinresponsetochangesinouradversaries’intent.

Assomestatesmodernizetheirnuclearcapabilities,theymaybetemptedtocompetewiththeUSintheareaofnuclearweapons.TheerosionoftheNuclearNonproliferationTreaty,militarydevelopmentsinChina,andNorthKorea’snuclearweaponscapabilitymaypushJapanandSouthKoreatoconsiderdevelopingnuclearweaponsoverthenext3to5years,therebyincreasingthelikelihoodofaproliferationcascade.Suchacascadeisnotinevitable,buttheprobabilityhasincreasedandshouldbeaddressedbyUSpolicymakers.Iran’sactionsalsothreatentocollapsenonproliferationefforts.Thus,theUSmustcontinuetocounterthreatsbymaintainingasafe,secure,reliable,andeffectivenucleardeterrentnot


For hedging against uncertainty, deterrence provides assurance

that rational adversaries will see the cost of attack as higher than

any benefits.

New Mexico Senator Jeff BingamanLANL Director Michael Anastasio LLNL Director George Miller

onlyasourdefense,butasthedefenseofouralliesaswell.Inessence,asafe,secure,andeffectiveUSdeterrentcurbsproliferation.Whiletheoverallsecurityenvironmentislesscertainthanitwas,assurancetoouralliesisstillavitalUSnationalsecurityobjective.Accordingtosomeexperts,nuclearweaponsalsomakeconventionalwarfarelesslikely.

TheUShedgeagainstsurpriseconsistsofnuclearwarheadscoupledwithacorrespondinginfrastructureandhumanresources.Relativetothecostofanattackandthebenefitsderived,deterrenceinfluencesthethinkingofouradversaries.Havingcredibletoolsinplacetoinfluenceouradversaries’goals,objectives,anddecisionsisallpartofthedeterrenceequation.Onemusthaveanaccuratewarningoftheintentaswellastheactionsofadversaries,andcommunicationmustbeconsistent,reliable,andaccuratewithadversariesandwithone’sownforces.Thoseforcesmustbereadyandcapableofacting.Andifdeterrencefails,thenthoseactionsmustbesufficientatleasttoachieveone’saims.Ensuringthatforcesaresufficientrequiresadaptability,tailoreddeterrence,andregularexercisesthatbuildcapabilityandconfidenceanddemonstratethatcapabilitytopotentialadversaries.

Ouragendamustalsoincludeemphasisonpreventingdiversionofnuclearmaterialsandweapons.Furthermore,weneedrenewedemphasisonourabilitytoattributetheoriginsofanymaterialsusedinanuclearattack.

What Are Our Hedging Options?Optionsforhedgingagainstanuncertainfutureincludetechnicaldiversity.Therehasbeenaninternationalconsensusfavoringfewernuclearstatesatthesametimethatthereisatrendtowardgreateravailabilityofnucleartechnology.Diversityamongoperationallydeployedandstockpiledwarheadtypeshelpsusintegratestrategicoffenseanddefensecapability.Reducednumbersofwarheadsdemandnewinvestmentinnuclearwarheads.Forexample,agingstockpilesmustbesustainedbyreplicatingcurrentdesignsand/ordevisingnewdesignstoachievethesamecapability.Thesesystemsmustberesponsive

tothenewsecurityenvironment(post9/11)confrontingtheUS.

Inaddition,warningtimecanbeincreasedbyourinvestmentinbetterintelligence,attackwarning,attackassessment,andgreaterrelianceoninternationaldata

exchangecenters.Notonlymustwerelyonouroperationallydeployedmechanisms,butwemustalsorelyonpolicytohelpmaintainabalanceofthecontinuingneedsofnucleardeterrenceagainsttheneedsofdiplomacybeingusedtoachievegreaternuclearsecurityandtocounterproliferation.

How Do We Counter Risk and Develop Effective Hedges?Thetwomostimportantrisksintoday’sstrategicclimatearethatdeterrencecouldfailandthattheUSmightfailtoprovideadequatesecurityassurancetoitsallies.


Arizona Senator Jon Kyl Vice Admiral Carl V. Mauney NNSA Admin. Thomas D‘Agostino

AprincipalhedgeagainstdeterrencefailureliesinthedegreeofintelligencetheUSpossessesaboutpotentialadversaries.Suchknowledgeincludestheirorganizationsandhierarchies,theirvalues,theirdegreeofdetermination,andwhetherornottheirstatescanbedeterred.Itisalsoimportanttoknowwhetherorhowtocommunicatedirectlyorindirectlywithpotentialadversaries.Itisnecessarytohavesuchunderstandingformanypotentialadversaries,andnonumberofweaponsorothermilitarycapabilityhasmuchvalueintheabsenceofsuchknowledge.Awiderangeofcommunicationandotherchannelsforinfluencingbehaviorsanddirectingsanctionsisvital.

Shoulddeterrenceactuallyfail,theUSneedsactiveandpassivemeanstodefenditselfandthecapabilitytoattributeanuclearattacktoanadversary.

Upsetstotheinternationalsecuritysystem,suchasintelligencefailures,helpusdevelophedgesthatminimizepotentialconsequencestotheUSandourallies.Suchsurprisesbecomeconsequencesforinternationalsecurity,forexample,underestimatingSovietpenetrationoftheManhattanProject,overestimatingthepaceofproliferationinthe1960s,underestimatingIraq’snucleareffortsin1991,andoverestimatingIraq’sweaponsofmassdestructioncapabilitiesin2001.TheUShedgesagainstpotentialfailureofkeyUStechnologiesandtechnologicalsurprisefromanadversarythattrulyunderminesourdeterrentstrategy.Hedgingagainsttheseuncertaintiesinvolvesmanythings,includingmaintaininganeffectivescientificandindustrialinfrastructureandkeytechnologiesessentialtodeterrence.

What Is the Path Forward?ThefirstissueregardingthepathforwardistheunclearfutureofnuclearweaponsaspartoftheUSdeterrenteventhoughthepathtoasmallernuclearweapons

inventoryisbecomingclear.Intheinterim,theUSnucleardeterrentisfundamentaltothesecurityofmanycountries.Thedebatecontinuesabouttheneedforconventionalweaponsoptionsratherthannewnuclearmilitarycapabilities.Conventionalweaponshavegreatdestructivepowerandofferagreaterrangeofoptionsthandonuclearweapons,butthetwotypesofweaponsarenotequivalent.Conventionalweaponscanbestabilizinginsofarastheyoffergreatrangeandcanrespondtosituationsquickly.

ThesecondissuerevolvesarounddifferentelementsoftheRussiannuclearposture.Forexample,wasthepushtowardde-alerting(makingreversiblechangestonuclearweaponssothattheycannotbedeployedrapidly)drivenbyconcernoverRussiancommandandcontrolweaknesses,andifso,howshouldtheUSdealwiththoseweaknesses?SomeconcernhasbeenexpressedthatRussianpoliticalandmilitaryposturingwithrespecttoneighboringcountriesproveddestabilizing,leadingtoacommonlyheldEuropeanviewthatnuclearweaponsareimportantbutdangerous.TheUSmustengageinseriousdiscussionswithalliesoversuchmatters.Withrespecttoarmscontrolobjectives,perhapssomeasymmetryinweaponsproductionmightbeacceptable.However,itshouldbenotedthatRussiaisnowproducingmorenuclearweaponsthantheUS.

Forhedgingagainstuncertainty,deterrenceprovidesassurancethatrationaladversarieswillseethecostofattackashigherthananybenefits.Yet,thereisuncertaintyinthegamutofadversariestodayanditishardtoknowwhatisintheirminds.Whenintentisunknown,wemustdealwithcapabilities.


Energy Balance in Fusion Hohlraums

Nuclearfusioncouldsupplyman’senergyneedsformillionsofyears.Fusionfuelscanbe

cheap,nonpolluting,ofalmostunlimitedsupply,uselesstoterroristsorroguestates,andunlikelytoprovokegeopoliticalconflict.Onesuchfusionfuelisdeuterium,anisotopeofhydrogenfoundinseawater.Thedeuteriuminagallonofseawatercouldproduceasmuchenergyas300gallonsofgasoline.And,dependingonthefuelcycle,theradioactivewasteproducedbynuclear-fusionreactorscouldbenegligiblecomparedwiththewasteproducedbynuclear-fissionreactors.

Presently,onlythecoresofstarsregularlyproducefusionenergyonalargescale.Hydrogenbombsalsoproducefusionenergyonalargescalebutonlybriefly,andtheirenergycannoteasilybefedintothegrid.Butthecurrentabsenceofnuclear-fusionpowerplantsisnotforscientists’lackofeffort.

Formorethan50years,scientistshaveworkedtoproducefusionenergyonEarthinacontrolledway.Inoneapproach,thefuel—intheformofahot,denseionizedgas(aplasma)—isconfinedbyamagneticfieldlongenoughforsignificantfusionreactionstooccur.Asecondapproachusesintensebeamsofphotons,electrons,orionstoheatandcompressthefuelveryrapidly;thefuel’smass,orinertia,confinesitlongenoughforsignificantfusionreactionstooccur.Thissecondapproachiscalledinertial-confinementfusion(ICF).

Recentadvancesinbothapproachesstronglysuggestthatnuclearfusioncouldbegintoplayasignificantroleinourenergyfuturewithinafewdecades,butsomedifficulttechnicalproblemsremaintobesolved.ThisarticleaddressesoneoftheoutstandingproblemsformanyICFexperiments,includingthoseabouttobeconductedatLawrenceLivermoreNationalLaboratory’sNationalIgnitionFacility(NIF).

NIF ExperimentsInexperimentsexpectedtooccurinthenextyearorso,NIF’s192pulsedlaserbeamswillpassthroughasmallholeateachendofahohlraum(Germanfor

“cavity”)—inthiscase,ahollowgoldcylinderaboutthesizeofapencileraser(seefigureonpage7).Thelaserbeamswillstriketheinnersurfacesofthehohlraum’swallsandheatthemtoveryhightemperatures.InthisindirectlydrivenICFtechnique,thehotinnersurfacesofthehohlraumwillthenemitx-raysthatwillcompress(implode)atargetcapsule—ahollow,BB-sizedsphereofberylliumorplasticsuspendedatthehohlraum’scenter.Thecapsulewillcontainfusionfuel—inthiscase,a50/50mixtureofdeuterium

andtritium(anotherhydrogenisotope).Ifallgoeswell,thefuelwillbesufficientlycompressedandheatedduringtheimplosionforasignificantnumberoffusionreactionstooccur.

Theefficiencyofthecompressionandburnwilldependontheconditionsinsidethehohlraum.Thoseconditionswillinturndependonhowmuchoftheenergydeliveredtothehohlraumremainsinsideitandhowmuchescapesaswall-emittedx-raysthroughholesinthehohlraum’swallthatinitiallyallowedenergytobedeliveredorallowdiagnosticinstrumentstoviewtheimplosion.Thelossofx-raysthroughtheseholeswillaffecttheenergybalanceoftheimplosionandcouldseriouslyaffecttheimplosion’squalityanditsfusionyield.

AteamofLosAlamosandSandiaresearchersstudiedthisx-rayleakageusingaspecialhohlraumdesignedforeasycomparisonofexperimentalmeasurementsofthex-rayleakagewithsimulationsofitperformedbyLASNEX,a2-DhydrodynamicscomputercodewidelyusedbyNIFandotherfusionresearchers.TheresultsofthesestudiescoulddirectlyimpactICFexperimentsatNIFandelsewhere.

Code-validation studies represent a necessary step to fully realizing

the potential of inertial-confinement fusion.


In the NIF experiments, the walls of a hohlraum will be heated by laser beams (left, blue beams). The inner surfaces of the hot walls will then emit x-rays that impinge on the spherical target capsule at the center of the hohlraum. The capsule’s outer surface will absorb the x-rays and explode, producing a reaction force that implodes the capsule and compresses and heats the fuel inside to densities and temperatures high enough for a fusion burn to occur. The hohl-raum’s walls could be heated instead by an external source of x-rays (right, solid red cones). Either way, the energy heating the walls’ inner surfaces will pass through an entrance hole at each end of the hohlraum. However, the x-rays emitted by the heated walls can also escape through these holes and other holes present to let diagnostic instruments view the implosion. X-rays that are lost through the holes or that are not emitted from the missing wall material where a hole is located can reduce the energy available to drive the implosion or cause nonuniform illumination of the capsule. Either effect can reduce the implosion’s efficiency and thereby reduce its fusion yield.

Laser beams

Laser beams

Hohlraum

X-ray beam

X-ray beam

Diagnostic holes

Target capsule

Radiation entrance hole

InLANL’sexperiments,theinnersurfacesofthehohlraum’swallswereheatedbyx-raysratherthanlaserbeams.Thesourceofthosex-rayswastheDynamicHohlraum(DH),drivenbytheZ-acceleratoratSandiaNationalLaboratoriesinAlbuquerque,NewMexico.TheDHsourcedeliveredapproximately100kJof200-eVx-raysintoasmallhohlraumplacedabovethesource.

Two-Way HolesWhenthex-raysemittedbythehohlraum’shotinnerwallsstrikethetargetcapsule,thecapsule’soutersurfacewillabsorbthex-raysandbequicklyheated.Theoutersurfacewillthenmelt,vaporize,andionize.Someoftheouter-surfacematerialwillflyradiallyoutwardathighspeed,essentiallyexplodingandproducingareactionforcethatimplodesthecapsule.

Iftoomuchx-rayenergyislostthroughtheholes,theimplosionwillbetooslowandthetemperatureoftheionsintheimplodedcapsulewillbetoolowforagoodfusionburn.

Thepresenceoftheholescanalsocausenonuniformilluminationofthecapsulebythewall-emittedx-rays.Theeffectsofnonuniformilluminationdependonwhathappenstothecapsuleduringtheimplosion.Astheoutsideoftheshellablates,nonuniformilluminationcanexcitehydrodynamicinstabilitiesintheablatedshellmaterial.Theseinstabilitiescandisrupttheshellifallowedtogrowtolargeamplitude.Ifaninstabilitybreaksuptheshellandcausesholestoformallthewaythroughit,fuelcanleakthroughthem.Thelossoffuelcanreducethefusionyield.Moreimportantly,materialfromthebrokenshellcaninjectimpuritiesintothefuelthat,onceagain,reducetheiontemperature—thistimethroughradiation—andtherebyreducethequalityofthefusionburn.

Studiesofx-raylossthroughholesinthehohlraumwallcanhelpdetermineexactlyhowtheyaffecttheimplosion’sefficiencyandsymmetry.Itisthereforecrucialtovalidatecomputer-codepredictionsofx-rayenergylossthroughtheholes.


Computer renderings of the 25-μm-thick copper hohlraum and the laser-driven x-ray-backlighter system used to image the hohlraum and its vicinity in these code-validation experiments. The 1-mm-diameter hole at the top of the hohlraum corre-sponds to the polar holes in the hohlraums illustrated on page 7. The 0.4-mm-wide circumferential gap in the hohlraum is the equivalent (for a 2-D simulation) of a midplane hole (see page 7). The part of the hohlraum above the gap is supported by three thin struts spaced equally azimuthally.

A pulse of 200-eV x-rays (solid red cone) from the DH radiation source enters the open bottom of the hohlraum. The pink hole in the lower tapered part of the hohlraum (the transport taper) gives an array of x-ray diodes a clear view of the x-rays entering the hohlraum. The inside of the hohlraum—from the bottom of the transport taper to the top of the hohlraum—is filled with 20-mg/cm3 silica aerogel to tamp inward motion of the copper walls, which are heated by the DH x-rays and ultimately become a hot radiating plasma. The semitransparent structure on top of the hohlraum is a 60-mg/cm3 silica-aerogel foam used as a diagnostic to follow the progress of blast waves produced by x-rays leaking from the hohlraum through the polar hole and the circumferential gap.

During an experiment, an intense laser pulse (red elipse in diagram at left) strikes a metal foil (gray rectangle in diagram at left), which then emits x-rays used to produce shadowgraphs of the blast waves. The backlighter x-rays are produced by shining the Z-beamlet laser at the Z-accelerator Facility onto a manganese foil. The backlighter x-rays have a very narrow energy spread centered at 6.15 keV due to the discrete radiative transition of the x-ray emission source and the use of a reflective Bragg crystal in the detection path. It is easier to uniquely determine a material’s density from x-ray attenuation if the x-ray energy spread is narrow rather than broad. Using x-rays with a narrow energy spread means the synthetic shadowgraphs we compare with experimental shadowgraphs can be more accurately generated from LASNEX’s calculations. The orange ellipse in the diagram at right suggests the areal extent of the source of backlighter x-rays generated by a laser source shown on the left. In real exper-iments, the red ellipse extends over a much larger section of the foil so the entire foam cap is backlit. A curved crystal that reflects and focuses the x-ray image of the backlit hohlraum onto a sheet of film is not shown. This setup produced the shadow-graph on page 9.

Follow the Blast WavesWehavevalidatedLASNEXbycomparingitspredic-tionswithexperimentalmeasurementsofx-raysescapingthroughapolarholeandacircumferentialgap—the2-Dequivalentofamidplanehole(requiredfora2-Dsimulation)—inthespecialhohlraumshownabove.

X-raysleakingoutthroughthepolarholeandthecircumferentialgapenterthesilicaaerogelencasingthetopofthehohlraum.(Silicaaerogelisaglassfoammuchlessdensethannormalsolidglass,inthiscaseonly10–20timesthedensityofroom-temperatureairatsealevel.)Asthex-raysentertheaerogel,theyproducesupersonicradiationwavesthatquicklybecomeblastwaves,whichgeneratedensityvariationsvisibleinx-rayshadowgraphssuchasthoseshown

onpage9.WehavevalidatedLASNEXbycomparingexperimentalmeasurementswithcodepredictionsoftheevolutionofthedensityvariations.

Getting a Clear Shot of the SourceToensurefidelityoftheLASNEXsimulation,thex-raysemittedbytheDHsourcemustbewell-characterized.Boththetemporalandspatialprofilesofthex-raysdeliveredtothehohlraumarerequiredsothatwecanuniquelycompareasimulationwithexperimentaldata.Toensurethatweknewtheseinputparameters,wemeasuredthex-raydrivewithanarrayofx-raydiodeslocatedsomedistancefromthehohlraum.Thediodeslookeddownthroughaholeinthex-raytransporttapershownabove.Theslantedcutoutsectionofaerogelgavethediodesanunobstructedviewofthex-raysource.However,theblastwavewasreflected

Laser spotMetal foil

Polar hole

Polar hole

Backlit area

Hohlraum

Transport taper

Transport taper

DH x-raysX-ray-diode port

Circumferential gap

Circumferential gapAerogel

Aerogel

Strut


An x-ray shadowgraph taken 14.5 ns after the DH x-rays entered the bottom of the hohlraum. Clearly visible are the blast waves (“bubbles”) produced by x-rays escaping through the polar hole and the circumferential gap in the special hohlraum. Note the asymmetry of the blast wave on the left caused by the removal of a section of aerogel to give an array of x-ray diodes a clear view of the DH source. The two vertical bars visible in the gap are two of the three support struts. The slanted lines are x-ray shadows of the undisturbed part of the wires used to create the imploding wire array in the DH x-ray source, which is located below the hohlraum.

A side-by-side comparison between the synthetic shadow-graph produced from LASNEX calculations (left) and the experimental shadowgraph (right) 14.5 ns after the DH x-rays entered the hohlraum.

fromtheslantedsurface,andthereflectedshockpropagatedbacktowardthecenterlineofthehohlraumtoproducetheasymmetryseenontheleftsideoftheexperimentalshadowgraphabove.Forthisreason,wecomparecoderesultsonlytotherighthalfofashadowgraphwherethecutawayandtheasymmetryitproducedwerenotpresent.

LASNEX’scalculationalspaceincludesthehohlraum,theaerogelinsideit,andtheaerogelencasingthetopofit.Asthe200-eVx-raystraveltothetopofthehohlraumthroughtheinternalaerogel,theyheattheaerogelandthecopperwall,whichthenemitsx-rays.Thewall-emittedx-rayscombinewiththeDHx-raysforthedurationoftheDHx-raypulsetogeneratetheearliestblastwavewhenthex-raysescapethroughthecircumferentialgap(firstframeinthefigureonpage 10)andamoredelayedblastwavewhenthey

escapethroughthepolarhole(secondframeonpage 10).Bothblastwavesthenevolvefurther,asseeninthelaterframes.Thedensityofthecopperwallchangeswithtimefromitsinitialvalue,butthewall,exceptforsomeradialinwardandoutwardexpansion,remainsreasonablyclosetoitsinitiallocation.

Theaerogelinsidethehohlraumtampstheradiallyinwardmotionofthewallmaterialtosomedegree.Iftheinternalaerogelwasnotthere,thecopperwallmaterialwouldcompletelycloseofftheinsideofthehohlraumwithinafewnanoseconds,atwhichpointx-raysfromtheDHsourcecouldnolongerenterthehohlraum.(Thegasinagas-filledNIFhohlraumservesasimilarpurpose,thatis,keepingthehohlraumopenforenergydeliverythroughoutthedurationofNIF’s26-ns-durationlaserdrive.)

Polar hole blast wave

Gap blast wave

Gap blast wave distorted by aerogel “Smoke rings”

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0.014920.022250.033180.049490.073820.11010.16420.24490.36540.54490.81281.2121.8082.6934.0236.000

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Six snapshots in time sequence from a LASNEX simulation of the evolution of the blast waves originating at the polar hole and the circumferential gap. In each snapshot, the local density is normalized to the initial density at that location to show how the material becomes more or less dense as the experiment evolves. In an experimental shadowgraph, densification produces a local increase in backlit-x-ray absorption. The same effect allows us to use the results of a LASNEX simulation to generate a synthetic shadowgraph.

Truth and ConsequencesAnimportantresultofthisstudyisthatLASNEX’spredictedpositionofthegap’sblastwaveasafunctionoftimeagreesuniquelywiththemeasuredvaluesonlywhentheDHx-rays’spatialdistributionandradiationtemperaturehistory,whicharebothinputtoLASNEX,agree,respectively,withthemeasuredspatialprofilefromashotwithoutahohlraumontopoftheDHsourceandtheactualmeasuredtemperaturehistoryontheshotbeingsimulated.

Moreover,theshadowgraphsonpage9showthatthemajorblast-wavefeaturesintheexperimentalshadowgrapharealsopresentinthesyntheticshadowgraphgeneratedfromtheLASNEXcalculations.Therearealsosomeobviousdifferencesbetweenthesyntheticandexperimentalshadowgraphs,suchasthetwo“smokerings”insidetheopengap,thatdonotappearinthesyntheticshadowgraph.Theringsareprobablylow-densitymaterialblownofftheedgeofthegapbyx-rays,justasmaterialisblownofftheoutersurfaceofthetargetcapsuleinaNIFexperiment.Wearestillstudyingthedifferencesbetweentheexperimentalresultsandthoseofthesimulations.

However,basedontheanalysiswehavedonesofar,webelievethatLASNEXcorrectlymodels• theenergylostthroughthepolarholeandthe

circumferentialgap,• thebehavioroftheblastwavesresultingfromthat

energyloss,and• thebulkradialhydrodynamicmotionofthewall.

However,assuggestedbytheexistenceofthe“smokerings,”somethingaboutmodelingthemetalblownoffthecopperwallmaybewrong.PossiblythewayLASNEXhandlescold-metalphysicscouldbeimproved.

Theresultsinthegraphbelowrevealanotherimportantresultofthestudy.Typically,thedesignerofafusion-hohlraumexperimentwillestimatethetime-dependentx-raypowerlostthroughaholeinthehohlraum’swallbymultiplyingthetime-dependentpowerdeliveredtothehohlraumbytheratioofthehole’sareatothetotalwallarea.

Comparison of simple areal estimates and LASNEX’s calcu-lations for the x-ray power lost through the polar hole and the circumferential gap. These results are for the shot that produced the shadowgraph on page 9.


Thegraphonpage10showsthatthepowerlosscalculatedbyLASNEXisdelayedcomparedwiththepowerlosscalculatedfromthearealestimates,whichscalethetime-dependentinputpowerby16.6%forthecircumferentialgapand4.36%forthepolarhole.Thedelayiscausedbythesilicaaerogel,whichdelaysenergydeliverytothewallinalocation-dependentmanner.Iftheaerogelwasnotpresent,thex-raylosscalculatedbyLASNEXwouldessentiallycoincideintimewiththeDHx-raydrivehistory.

At10.5nsaftertheDHx-raysenteredthehohlraum,19.24kJofx-rayenergyhadbeendeliveredtothehohlraum.LASNEXcalculatedthat3.42kJofx-rayenergyhadbeenlostthroughthecircumferentialgapand0.65kJthroughthepolarhole,comparedwitharealestimatesof3.2kJforthegapand0.84kJforthehole.So,thelossescalculatedbyLASNEXcanbelargerorsmallerthanthesimplearealestimates,dependingonwhereaholeorgapislocated.

Theaerogel(oraNIFgasfill)ensuresthatenergycanbedeliveredtothehohlraumforthefulldurationofthedrivepulse,buttheaerogelalsointroducesacomplication:theenergydeliveredtoaparticularlocationonthehohlraumwallwilldependonthatlocation.Thiseffectcouldpotentiallychangethetemporalhistoryofthex-raysilluminatingthetargetcapsule,whichcoulddelaytheimplosionorproduceanasymmetricimplosion.Eithereffectcouldreducetheimplosion’sefficiency.

Althoughtheeffectsoftheaerogelonthepeakamplitudeandtimehistoryofthepowerlostthrough

theholesarerelativelysmall,theycouldaffectthedetailedbehavioroftheimplosionandthediagnosticsetup.Wethereforesuggestthatsimplearealestimatesofthex-raypowerlostthroughholesinthehohlraum’swallscanbeusedearlyinthedesignofanexperiment.Beforeanactualshot,thepredictedholelossesasafunctionoftimeshouldbestudiedcarefullysothatdiagnosticinstrumentscanbeproperlysetupandimplosiontimescanbeaccuratelyestimated.

Toward Viable Fusion ReactorsControllednuclearfusionhasgreatpotentialasaneconomical,nonpolluting,proliferation-proof,andnearlyinexhaustiblesourceofenergy.Fusionreactorscouldbesupplyingsignificantamountsofourenergyneedsbythemiddleofthiscenturyorearlier—butonlyifdetailssuchastheeffectsofx-rayleaksfromfusionhohlraumsarecarefullystudiedandresolved.TheLASNEXcode-validationstudiesdescribedherethusrepresentanecessarysteptofullyrealizingthepotentialofinertial-confinementcontrollednuclearfusion.

Point of contact: Bob Watt, 505-665-2310, [email protected]

Other contributors to this work are George Idzorek, Tom Tierney, Randy Kanzleiter, Robert Peterson, Darrell Peterson, Bob Day, Kimberly DeFriend, the Los Alamos Target Fabrication and Assembly Team, Mike Lopez, Michael R. Jones, and the entire Z-accelerator operating crew at Sandia National Laboratories in Albuquerque, New Mexico.


Upgrades Made to the Trident Laser Facility

UpgradesmakeLANL’sTridentLaserFacilityoneofthemostpowerfulhigh-energylasersintheUS.

TheTridentenhancementteam’sfirstgoalwastoenableexperimentsattheTridentLaserFacilitythatwouldadvanceLANL’shigh-energy-density(HED)physicsprogram.Also,theteamhadthefollowingtwoprimaryperformanceobjectives:• generate18–35keVx-raysofsufficientdosetoilluminateanx-ray

detector(seePlasmaExperimentsandDetectors)and• generateintenseionbeamswithenergiesgreaterthan1MeV/amu.

Theteam’sfinalgoalwastocontinuetooperatethefacilityefficientlyandtoincreasethenumberofinnovativescientificexperimentsconductedbyLANLandexternalexperimentalteams.


Plasma Experiments and Detectors InatypicalTridentexperiment,twolaserbeamsstrikeatargetmaterialinsideavacuumchambertogenerateaplasma.Thethirdbeamisshinedthroughtheplasma.Asthethirdbeampassesthroughtheplasma,theinteractionofthebeamwiththeplasmaionsgeneratesx-rays,whicharerecordedwithanx-raydetector.

Currentdetectortechnologyusesx-rayframingcamerasthatarecomparabletodigitalcameras—onlyinsteadofrecordingvisiblelight,thesecamerassensex-raysandthenamplifyandconvertthemintovisiblelight.Thex-rayframingcameracapturesafixednumberofextremelyshortexposuresinarapidseries.Opticalandparticleemissionsfromtheplasmaarealsorecordedusingvarioushigh-speed(16 billionframes/s)cameras.

Intermediate-Scale Laser FacilitiesHEDsciencehasbeenbroughttotheforefrontofscientificresearchwiththecompletionoftheNationalIgnitionFacility(NIF)andthebeginningofinertial-confinementfusion(ICF)experiments.Large-scaleHEDresearchfacilitiessuchasNIF,whichhas192converginglaserbeams,andtheUniversityofRochester’sOmegaLaserFacility,whichhas60converginglaserbeams,provideresearcherswiththehighestenergy-densityconditionscurrentlypossibleinthelaboratory.

Researchatanintermediate-scalefacility,liketheTridentFacility,providesscientificfoundationsfornationalgrandchallengeresearch,e.g.,fastignitionandlaser-basedaccelerators,atlarge-scalefacilities.Intermediate-scalefacilitiesalsoallowmoreefficientuseoflarge-scalefacilitiesbyprovidingaplatformforexperimentalanddiagnosticdevelopmentusingrelevantplasmaconditions.Becauseintermediate-scalefacilitieshaveversatilityandflexibilitynotpossibleatlarge-scalefacilities,theyareessentialtothefutureofHEDplasmaphysics.Intermediate-scalefacilitieshaveflexiblebeamlineanddiagnosticconfigurationsthatenabletheinvestigationofhigh-risk/high-payoffideas—particularlyinresearchareasthatdonotfitintotheparametersofalarge-scalefacility’smission.High-riskexperimentsarealsomadepossiblebythehighshotrate,modestcosts,andHEDplasmaconditionsrelevanttothoseobtainedatlarge-scalefacilities.Flexibilityandhighshotratealsomakeintermediate-scalefacilitiesidealfordevelopingdiagnosticequipmentandtechniquesnecessaryforeffectiveexperimentsatthemoreexpensivelarge-scalefacilities.

Trident HED FacilityTheTridentFacilityisdedicatedtoHEDphysicsexperimentsandlasertechnologyresearch.Thisfacilityconsistsofathree-beam,high-energylasersystemandexperimentaltargetchambers.ThehallmarkoftheTridentFacilityisitsflexibleilluminationgeometry,pulselengths,anddiagnosticconfigurations.

Trident’sthreeinfraredbeamscanbeindividuallyfocusedontoanHEDtarget.Twobeamsoperateinlong-pulsemode,thatis,theygeneratelightpulsesthatlastbetween1nsand10,000ns.Thethirdbeamcanoperateineitherlong-pulse(1–10,000ns)orshort-pulse(~0.0005ns)mode.Flexiblepulselengthsenableawiderangeofexperiments,includingstudiesofradiationhydrodynamics,laser-plasmainteractions,andlaser-launchedflyerplatesforcreatingveryhighpressureandveryhighstrainratesinmaterialsamples.

Eachlaserbeamcanbedirectedintoeitheroftwotargetchambers(athirdchamberisbeingcommissioned,seeFlexibleUserFacility).Experimentscanoccurinbothchamberssimultaneously,alternately,orallthreebeamscanbedirectedtoonetargetchamber.Eachbeamcanbeconvertedwithanonlinearopticalelementtoproducegreenlaserlight.Thethirdbeamcanalsobeconvertedtoultravioletlight.Thevaryingwavelengthsofinfrared,green,andultravioletlaserlightenableadvanceddiagnostictechniquesthatotherwisewouldnotbepossible.

FundamentaldiscoveriesandfirstobservationsfromTridentexperimentsincludemonoenergeticfast-ionacceleration,fluid/kineticnonlinearbehaviorofplasmawaves,electron-acousticwavescattering,energeticprotonaccelerationwellbeyondthepowerscalingfoundintheliterature,thefirstobservationoftheion-acousticdecayinstability,andthefirstobservationofionplasmawaves.


The Trident Facility provides three target chambers for experiments. The west target chamber (top) will be used extensively for short-pulse experiments. The north target chamber (top right) is used for diagnostic development and short-pulse experiments. The large rectangular vacuum chamber contains the dielectric compression gratings that compress a laser pulse to less than 1 ps in duration. The south target chamber (bottom) is used extensively for materials science and laser-matter interaction experiments.

Flexible User FacilityProvidingflexibility,yetkeepingtheuserinterfacesimple,requirescomplexoperationofTrident’slaserandtheexperimentaltargetareas.Eachofthethreelaserbeamlinescanbedirectedintoanyoneoftwovacuumchambers(targetchambers)wherethelaserwillstrikeatargetmadeofvariousshapesandmaterialsforeachexperiment.

Eachtargetchamberprovidesconfigurations,illuminationgeometries,anddiagnosticaccessthatcanbecustomizedforparticularexperiments.Thesouthtargetchamberisahorizontalcylinderwithadiagnostictableinsidethechamber.Mirrors,spectrometers,andotherdiagnosticequipmentcanbelocatedanywhereonthistable.Thelaserbeamscanenterthetargetchamberthroughmanyports.Researchersprimarilyusethischamberfordynamicmaterialexperimentssuchaslaser-launchedflyerplateandlaser-ablationshockloadingexperiments.Scientistsalsoperformlaser-plasmainteractionexperimentssuchastheinteractionofashortpulse(5 ps)withagasjetformedintoplasmaby1or2long-pulse(1ns)beams.

Thewesttargetchamberisbeingcommissionedin2010.Thischamberisdesignedspecificallyforshort-pulseexperi-ments.Itisa10-sidedchamberwithalargeopticaltableinsideforextremelyflexibleexperimentalgeometries.

Thenorthtargetchamberissphericalandisusedfordiagnosticdevelopmentandcurrentshort-pulseexperiments.Attachedtothistargetchamberisaten-inchinstrumentmanipulator(TIM)thattransportsdiagnosticsintoandoutofthevacuumchamber.ThisTIMisidenticaltotheonesattheOmegaLaserFacilityandiscompatiblewiththemanipulatorsatNIF.Thus,diagnosticsdevelopedandbuiltforOmegaorNIFcanbetestedandqualifiedonTridentwithoutusingvaluabletimeatthoselargerfacilities.

Withthreetargetchamberstochoosefrom,researcherscandesigneachexperimenttomaximizedatareturnandtoprovidedatathatiseasilyinterpreted.Inaddition,multiplechambersincreaseefficiencybecauseanexperimentcanbesetupinonechamberwhileanotherexperimentisbeingperformedinadifferentchamber.Finally,experimentscantakeplaceintwochamberssimultaneously.


EnhancementTrident’sthirdbeamcannowproducelaserpulseswithpeakpowersofupto0.2PW.Reachingthispowerlevelrequiredmanycomponentupgrades.Beginningatthefrontendofthelaser,theenhancementteamreplacedtheoscillatorthatproducesthe“whitelight”seedpulse(seeLaserBeamAmplificationandCompression). Apairofopticalgratingsincreasesthedurationofthebeam’spulsebyseparatingitintoitscomponentwave-lengths,whichstretchesoutthepulseintimeandtheninjectsitintotheamplifierchain(thenextsegmentofthelaser)wheretheenergyofthepulseisincreased.

ToallowTridenttofocusthepulseonasmallspotonthetargetandthusincreasetheresolutionofradiographs,thefacilityenhancementteamplacedadeformablemirrorintheamplifierchaintocorrectdistortionsinthelaserbeamcausedbythermalheatingoftheamplifiers.Thedeformablemirroriscomputercontrolledandallowsresearcherstochangetheshapeofthemirror,therebyimprovingtheopticalqualityofthelaserpulse.Theteamalsoincorporatedadditionalamplifierstoincreasetheenergyofthethirdbeamto

Laser Beam Amplification and Compression Everylaserbeamstartswithalow-powerseedlaserpulseinitiatedfromatabletoplasergeneratorcalledamasteroscillator.Thisseedlaserpulseexhibitsthegeneralcharacteristicsofthefinallaserpulse(e.g.,wavelengthandpulseshape),butatamuchlowerenergy.Alaser’struepowerisbasedonthefactthatitproducesacoherent(thelightphotonsarecorrelatedinspaceandtime)beam(lightwavesareorientedinthesamedirectionanddonotdiffuserapidly).

Thepurposeofstretchingandthencompressingthelaserbeamistopreventdamagingtheglassintheamplifiers.Thenthelaserfacilityamplifiestheseedlaserpulsetotherequiredpowerlevel.Toincreasetheenergyintheseedpulse,ittravelsthroughseveralstagesofamplification.Eachstageconsistsofglassdisks.Inanamplifier,electricalenergyistransferredtotheamplifierswithflashlamps(likethoseonacopiermachine).Thelightfromthelampsisabsorbedbyglassdisksandthentransferredtothelaserpulseasitpassesthroughtheamplifierdisks.

Amplificationincreasestheenergycontainedinthebeamthatisdeliveredtothetarget.Compressionincreasesitsintensitybydeliveringallofthatenergyinamuchshortertime.

morethan100Jfromitspreviouslimitof30J.Finally,inordertoalloweasyaccesstoallcomponentsinthelaserbeamandtargetbays,theteamelevatedthebeamtransportsystemsothatitscomponentsaremorethan6ftabovethefloor.

Thelaserbeamentersanopticalperiscopewhereitsheightisloweredto4ftabovethefloorandthenentersa5ft×5ft×10ftvacuumchamber.Withinthischamber,asetofverylargeopticalgratings(largepiecesofglassthathavemorethan600lines/mmetchedintothem)compressesthedurationofthepulse

tolessthan600fs.Byreversingthestretchingprocessexactly,thevariouscolorsofthebeamarerecombinedintotheoriginalshortpulse.Becausetheintensityofthelaserpulsewillcauseairbreakdown(moleculesofairionizeanddegradethecoherenceandshapeofthelaserpulse),thelaserbeammustremaininavacuumaftercompression.Thecompressedlaserpulseisthentransportedtoatargetchamberandfocusedontothetargetbyanoff-axisparabolicmirror.

The hallmark of the Trident Facility is its flexible illumination geometry, pulse lengths,

and diagnostic configurations.

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)Thecombinationofthedeformablemirrorandahigh-qualityfocusingmirrorproducesalaserspotonthetargetthatis~13µmindiameter,whichis5to10timessmallerthanthelaserspotsproducedbytheOmegaorNIFlasers.Duringcommissioning,Tridentproducedpulsesasshortas550fsthatwereamplifiedto100J.Sincecompletionoftheupgrade,scientistsroutinelyproducepulsesgreaterthan0.2PWonceanhour.

Experiments Prove Enhancements’ ValueAfterenhancementswerecompleted,theTridentFacilitymettheexperimentalobjectivesforx-rayback-lighting(i.e.,radiographinganobjecttodeterminethepositionofshockwaves)andproducingintensehigh-energyionbeamsinthefirstmonthofoperation.Theseobjectivesarediscussedinthenexttwosubsections.

Energetic X-rays Probe HED PhenomenaWhenthelaserstrikesaflatorcurvedthinfoil,atomsinthefocalplaneofthe0.2-PWlaserareexposedtoa3000-V-per-atomic-diameterelectricfield.Suchanextremeenvironmentripstheelectronsfromtheatomsandacceleratesthemalmosttothespeedoflightinashorttimeanddistance.Whentheseelectronsstrikenearbymaterial,theyproducex-rays—eachwiththecharacteristicsignatureofthenativeatom.

Thesex-raysareusefulasresearchersexaminehydrodynamiceffects(calledhydrodynamicbecausethematerialsflowlikeafluid)inexperimentsinvolving

Signature spectra of zirconium, silver, and tin excited by laser-driven electrons that approach the speed of light. A mono-chromatic (consisting of electromagnetic radiation that has an extremely small range of wavelengths) x-ray source (e.g., the signature spectra of tin, 26 keV) simplifies measuring the density of materials in physics experiments.

High-energy photon (22 keV) radiography using Trident’s third laser beam in short-pulse mode. High-energy photons are needed to penetrate very dense objects. This radiograph of a gold grid shows excel-lent spatial resolution (~10 μm). The ability to make small features within the plasma visible and distinct is critical to validate physical models.

densematerials.SuchexperimentsarenowpossiblebecauseTridentisapetawatt-classlasercapableofcreatingasufficientfluxofenergeticx-rays.Theexperimentsrequireshortx-rayexposuresbecausethe1-nshydrodynamicphenomenaoccuronnanosecondtimescales.Becausethex-rayburstisshorter—approximately1ps—thelaser-generatedx-rayfluxisidealforpenetratingextremelydensematerialsandeliminatingmotionblurfromradiographicimages.

Researchersobtainedaproof-of-principlex-raypinholecameraradiographofagoldgridwith22-keVx-raysproducedfromasilvertarget.Theexcellentspatialresolution(~10µm)isduetothesmallsize(~13-µmdiameter)oftheTridentlaserfocalspot.Thisx-raybacklightingcapabilityisoneofthekeystrengthsoftheTridentFacility.

Energetic Proton Beams ProducedTheTridentshort-pulseenhancementpermitsirradiationoftargetswithupto1020W/cm2oflaserlightbecauseofthebeam’s• highenergy(100J),• shortpulsewidth(550fs),and• smallfocalspot(~13-µmdiameter).

Thiscapabilityenablesasolidtargettoemitveryenergeticprotons.

InthefirstexperimentdesignedtoproduceaprotonbeamontheenhancedTrident,manymoreprotonswithhigherenergieswereproducedthanexpected.Higherenergieswillallowadditionalphysicstobeexplored(e.g.,fastignition)usingthehighestpowersavailable;theywillalsoallowexperimentsatsmallerlaserfacilitiestoaccessHEDregimesnotpreviouslythoughtpossible.Theprotonenergiesmeasuredexceedarecentlyproposedscalinglawbyafactorof10below1 ×1019W/cm2andexceedthoseofsimilarlasersystemsabove1×1019W/cm2.

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The angle- and time-integrated energy spectrum of the beam can also be determined from radiochromic film stack data. The darkness of each piece of film indicates the total number of protons at each energy. (Horizontal red lines are error bars. Data are binned into 3-MeV intervals.) A material will stop and absorb a proton at a certain distance that is a function of both the material’s properties and the energy of the proton. A broad spectrum of protons means that the energy in the beam will be absorbed over a large depth in the material. If the beam was monoenergetic, i.e., having essentially a single energy, the beam would be absorbed in a very small volume of the target material. Tailoring where the energy is deposited by choosing the proton energy and the spectrum of the beam is essential for medical applications such as tumor treatment.

1.6 MeV 3.5 MeV 13.1 MeV 18.9 MeV

23.5 MeV 27.4 MeV 31.1 MeV 34.3 MeV

37.4 MeV 40.2 MeV 42.9 MeV 45.5 MeV

47.9 MeV 50.3 MeV 52.6 MeV

Proton energies achieved at Trident (the data points) exceed the recently proposed scaling law (solid line) at lower laser intensities. Improvements in the facility, including lower prepulse levels, enable higher-energy protons to be produced at lower laser intensities. This increased efficiency opens new opportunities for physics research in biomedical applications, weapons physics, and fast ignition.

A 50.3-MeV proton beam imaged on a radiochromic film stack produced from a 10-μm-thick molybdenum foil target irradiated at 4.6 × 1019 W/cm2. Each layer of film stops protons of lower energy. For example, any protons reaching the 14th piece of film must have an energy of at least 50.3 MeV. The next film is at beam energy of 52.6 MeV; thus the final energy is known only to the certainty of 2.3 MeV (i.e., the beam energy was less than 52.6 MeV and greater than 50.3 MeV). The size of the spot (well-defined dark area) shows the divergence of the proton beam. (The more diffuse background shaded area is the contribution from hot elec-trons [1–10 MeV].) At very high energies, the spot is small—showing that the higher-energy protons are well collimated.


TridentprovidesaflexibleexperimentalfacilityforthestudyofnewlyconceivedHEDphysicssuchasx-rayThomsonscatteringtodeterminethecharacteristicsofwarmdensematter.ThesuperiorperformanceoftheTridentlasersystemcanbeattributedtolowlaserprepulsethatcreatesasmallplasmaatthesurfaceofthetargetbeforethemainpulsereachesit.Bymeasuringtheseedlaserpulsebeforeamplification,thecontrastbetweenthemainlaserpulseandanyprecursorpulsesisinferredtobegreaterthan107.TheTridentlaser’spulseduration,spectrum,near-fieldpattern,andfar-fieldpatternaremeasuredandrecordedforeachshot.RapidcomputeranalysisoftheselasersystemperformancedatamakestheTridentFacilityoneofthebestdiagnosedhigh-energy,short-pulsesystemsintheworldandallowsfacilitystafftomaximizelaserperformancebymakingslightcorrectionstothoseparametersbeforeeveryshot.

Points of contact: Randy Johnson, 505-665-5089, [email protected] David Montgomery, 505-665-7994, [email protected]

Itisimportanttomeasurethepropertiesoftheprotonbeamtooptimizeproductionofthebeamandtoaidinmodelingandpredictinginteractionofthebeamwithatargetmaterial.Astackofradiochromicfilmsistheprimaryinstrumentusedtomeasurethebeam’sproperties.Inthisexample,16piecesoffilmshowaprotonbeamcreatedfromtheinteractionoftheshort-pulselaserwithamolybdenumfoiltarget.Fromthesedata,researchersdeterminethemaximumenergyofthelaserandthenumberofprotonscreated.Theenergyspectrumoftheprotonsisderivedusingdataobtainedfromthefilmimages.Thebeamcontainsapproximately3.5Jofenergyinprotonsabove4MeV,i.e.,approximately4%ofthetotallaserenergy,whichisaveryhighefficiency.Incomparison,theefficiencyofgeneratingx-raysfromsuchfoils,asdiscussedintheprevioussection,isoftheorderof1%orless.

ThehighestrecordedprotonbeamenergyobtainedatTrident,50.3MeV,rivalsthehighestpreviouslyrecordedenergyobtainedatLLNL’sNovaPetawattLaserFacility(nowdecommissioned),whichreported58MeV,butrequired5timesthelaserenergyandintensityontarget.Trident’sconversionefficiencyis2 to8timeshigherthansimilarlasersystemsatthislaserintensitywith3timesgreaterproton-beamenergy.


Fogbank: Lost Knowledge Regained

DuringJapan’sMuromachiperiod(1392–1573),swordsmithsdevelopedthekatana,often

calledthesamuraisword,whichwasfabricatedfromspecialsteel.Secrettechniquesinquenching,tempering,andpolishingmadetheswordoneofthedeadliestonanybattlefield.

Inthe16thcentury,firearmswereintroducedtoJapan.Expertswordsmiths,whoseskillshadbeenacquiredfrompreviousgenerations,werenolongerneeded.Thus,theskillsassociatedwithmakingsuchdeadlybladeswerelost.

Today,thescienceofmetallurgyisadvancedenoughsothatresearchersunderstandtheprocessingvariablesthatgavethekatanaitsdistinctproperties.Moreover,scientistscanreplicatetheprocessestoagreatextentbyusingmodernmethods.

Likethekatana,amaterialknownasFogbankhasundergoneasimilarsequence.Producedbyskilledhandsduringthe1980s,Fogbankisanessentialmate-rialintheW76warhead.Duringthemid-1990s,Fogbankproductionceasedandthemanufacturingfacilitywasdismantled.Astimepassed,theprecisetech-niquesusedtomanufactureFogbankwereforgotten.

WhenitcametimetorefurbishtheW76,Fogbankhadtoberemanufacturedorreplaced.In2000,NNSAdecidedtoreestablishthemanufactureofFogbank.OfficialschosetomanufactureFogbankinsteadofreplacingitwithanalternatematerialbecauseFogbankhadbeensuccessfullymanufacturedandhistoricalrecordsoftheproductionprocesswereavailable.Moreover,LosAlamoscomputersimulationsatthattimewerenotsophisticatedenoughtodetermineconclusivelythatanalternatematerialwouldfunctionaseffectivelyasFogbank.

AlthoughFogbankisadifficultmaterialtomanu-facture,scientistssoondiscoveredthatrestoringthemanufacturingcapabilitywouldproveanevengreaterchallenge.Scientistsfacedtwomajorchallenges:• mostpersonnelinvolvedwiththeoriginal

productionprocesswerenolongeravailable,and• anewfacilityhadtobeconstructed,onethatmet

modernhealthandsafetyrequirements.

Despiteeffortstoensurethenewfacilitywasequiv-alenttotheoriginalone,theresultantequipmentandprocessingmethodsfailedtoproduceequiva-lentFogbank.Thefinalproductsimplydidnotmeetqualityrequirements.

Personneltookamorecarefullookatthedesignofthenewfacility,comparingitcloselywiththeoldone.Theydiscoveredthatsomeofthehistoricaldesignrecordswerevagueandthatsomeofthenewequipmentwasequivalent,butnotidentical,totheoldequipment.Differencesthatseemedsmallduringthedesignphasebecamemoresignificantoncethenewfacilitybegantoproducematerial.Thesituationwasexacerbatedbyconstructiondelays,whichputtheprojectayearbehindschedule.

AstheoriginaldeadlinequicklyapproachedinMarch2007,manyadditionalresourceswereengagedwhenanemergencyconditionwasestablishedforFogbankproduction.Personnelmademultiplechangestomultipleprocessessimultaneously.TheresultwasproductionofequivalentFogbankandrecertificationoftheproductionprocessin2008.

Despitethissuccess,personnelstilldidnotknowtherootcauseofthemanufacturingproblems.Infact,theydidnotknowwhichprocesschangeswereresponsibleforfixingtheproblem.Afterproductionwasreestablished,personnelimplementedprocessstudiesinanattempttodeterminetherootcause.Thesestudiesproveddauntingbecause• theprocessesarecomplexanddependoneach

other,and• thematerialcharacteristicsthatcontrolqualityof

thefinalproductwerenotunderstood.Personnelformedahypothesisfortherootcauseofthemanufacturingproblemsbycombiningresultsfromrecentstudieswithinformationgatheredfromhistoricalrecords.HistoricalinformationindicatedthatoccasionallytherewereproductionproblemswithFogbankforwhichtherootcausecouldnotbesatisfactorilyresolved.Thehistoricalproductionproblemsweresimilartothoseobservedwhenreestablishingproduction.


To fabricate new Fogbank, modern scientists reconstructed the historical manufacturing process (top). However, when the resultant Fogbank assembly did not meet quality requirements, scientists analyzed the historical manufacturing process and discovered one minor difference that, when adjusted properly (bottom), yielded quality Fogbank.

WheninvestigatinghistoricalrecordswithrespecttoimpuritylevelsduringtheFogbankpurificationprocess,personneldiscoveredthatinsomecasesthecurrentimpuritylevelsweremuchlowerthanhistoricalvalues.Typically,lowerimpuritylevelsleadtobetterproductquality.ForFogbank,however,thepresenceofaspecificimpurityisessential.

LaboratorydatashowthatthepresenceofoneparticularimpurityintheFogbankpurificationprocessplaysanimportantroleinthequalityofthefinalmaterial.Theimpurity’spresenceinsufficientquantityresultsinadifferentmorphology(formandstructure)ofthematerial.Althoughthechangeinmorphologyisrelativelysmall,itappearstoplayanimportantroleinthedownstreamprocesses.Areviewofthedevelopmentrecordsfortheoriginalproductionprocessrevealedthatdownstreamprocesseshadbeenimplicitlybasedonthatmorphology.

However,historicalrecordslackedanyprocesscontrolsdesignedto• ensurethatthepurificationprocessproducedthe

impuritymorphologyor• evaluatethesuccessofsomeoftheimportant

processes.Currently,personnelareproposingadditionalprocesscontrolsdesignedtocheckbothmorphologyofthematerialandtheeffectivenessofthedown-streamprocesses.

Furtheranalysesoftherestartactivitiesrevealedthattherewasasmallvariationinthefeedmaterialusedinthepurificationprocess.Thisvariationledtothechangeinimpuritycontentandthustheresultantchangeinmorphology.Scientistsfoundthatmoderncleaningprocesses,usedinthemanufactureofthefeedmaterial,cleanitbetterthanthehistoricalprocesses;theimprovedcleaningremovesanessentialchemical.

Historically,itwasthischemicalthatreactedduringpurificationofthefeedmaterialtoproducetheimpuritynecessaryforpropermorphology.ThehistoricalFogbankproductionprocesswasunknowinglybasedonthisessentialchemicalbeingpresentinthefeedmaterial.Asaresult,onlyamaximumconcentrationwasestablishedforthechemicalandtheresultingimpurity.Nowthechemicalisaddedseparately,andtheimpurityconcentrationandFogbankmorphologyaremanaged.

JustasmodernscientistsunraveledthesecretsbehindtheproductionoftheJapanesekatana,materialsscientistsmanagedtoremanufactureFogbanksothatmodernmethodscanbeusedtocontrolitsrequiredcharacteristics.Asaresult,FogbankwillcontinuetoplayitscriticalroleintherefurbishedW76warhead.

Point of contact: Jennifer Lillard, 505-665-8171, [email protected]

Reconstructed Process

Purification of feed material

Process U

Process V

Process X

Process Y

Process Z

Assembly

Chemistry test

Physical test

Purification of feed material

Process U

Process V

Process X

Process Y

Process Z

Assembly

Adjusted Process

Morphology

measurementProcess

effectiveness

check

Chemistry test

Physical test

Add essential

chemical


The Los Alamos Branch of the Glenn T. Seaborg Institute for

Transactinium Science

The modern periodic table of the elements. Actinium (element 89) through lawrencium (element 103) are the actinide elements.Rutherfordium (element 104) through the most recently discovered element (element 118) are the transactinide elements. Trans-actinium elements include the actinide and transactinide elements.

T hetransactiniumelements—whichincludeactiniumthroughlawrencium(theactinides)and

rutherfordiumthroughthemostrecentlydiscoveredelementwithatomicnumber118(thetransactinides)—compriseapproximately24%ofallelementsintheperiodictable.Mostofthetransactiniumelementsaremanmadeandallareradioactive,makingtheirstudyachallengingandhighlyspecializedfieldofscience.

Threetransactiniumelements—uranium,neptunium,andplutonium—havealwaysbeenparticularlyimportantatLosAlamos,beginningwiththe

ManhattanProjectandcontinuingtothepresentday.Overtheyears,fundamentaltransactiniumsciencehasbeenusedtochemicallyprocessandseparatethesematerials,manipulatetheirphysicalproperties,characterizethem,anddetecttheminsupportofmanyLosAlamosmissionareas,mostrecentlyincludingstockpilestewardship,environmentalstewardship,homelandsecurity,andenergysecurity.

Realizingtheimportanceofthetransactiniumelementstoavarietyofnationalsecuritymissions,agroupofUSscientistsestablishedtheGlennT.Seaborg

1

H2

He3

Li4

Be5

B6

C7

N8

O9

F10

Ne11

Na12

Mg13

Al14

Si15

P16

S17

Cl18

Ar19

K20

Ca21

Sc22

Ti23

V24

Cr25

Mn26

Fe27

Co28

Ni29

Cu30

Zn31

Ga32

Ge33

As34

Se35

Br36

Kr37

Rb38

Sr39

Y40

Zr41

Nb42

Mo43

Tc44

Ru45

Rh46

Pd47

Ag48

Cd49

In50

Sn51

Sb52

Te53

I54

Xe55

Cs56

Ba57

La*72

Hf73

Ta74

W75

Re76

Os77

Ir78

Pt79

Au80

Hg81

Tl82

Pb83

Bi84

Po85

At86

Rn87

Fr88

Ra89

Ac**104

Rf105

Db106

Sg107

Bh108

Hs109

Mt110

110111

111112

112113

113114

114115

115116

116118

118

*Lanthanides58

Ce59

Pr60

Nd61

Pm62

Sm63

Eu64

Gd65

Tb66

Dy67

Ho68

Er69

Tm70

Yb71

Lu

**Actinides90

Th91

Pa92

U93

Np94

Pu95

Am96

Cm97

Bk98

Cf99

Es100

Fm101

Md102

No103

Lr


TheEnhancedSurveillanceCampaign(ESC)wastaskedwithprovidingdiagnostictoolsforearlydetectionofpotentialage-induceddefectsinnuclearweapons’components.Thiscampaignsupportedmanyofthecriticalskillsandmuchoftheexpertiseinmaterialssciencefortheweaponscomplex.Changesinweaponsperformancethatresultfromagingrepresenttheendofaseriesofeventsthatbeganyearsordecadesearlier.Changesoccurfirstintheatomic-scalepropertiesofthematerialswithintheweapons—propertiessuchascomposition,crystalstructure,andchemicalpotential.Changesareobservedlaterinthematerials’large-scalepropertiesthatareimportanttoapplications—propertiessuchasdensity,compressibility,strength,andchemicalreactionrates.

TheESCcontributestothescientificandtechnicalbasesfortheannualassessmentofagedcomponentsandforrefurbishmentdecisionsandschedules.UndertheauspicesoftheInstitute,theprogramsuccessfullyreplicatedtheRockyFlatswroughtprocessforplutoniumpitsandcastseveralkilogramsofaccelerated-agedplutoniumalloythatachieveda60-yearequivalentageinlessthan4years(seetheActinide Research Quarterly2ndquarter2002).

TheInstitutealsoorganizedaseriesofpit-lifetimeworkshopsandprogramreviewsbetweenLANLandLLNL.Thepit-lifetimeworkshopsspanneda5-yearperiodandprovidedaforuminwhichtodiscussallrelevantLANLandLLNLdata,toinvolveawider

InstituteforTransactiniumScienceatLLNLin1991(seetheActinide Research Quarterly2ndquarter2009,onlineathttp://arq.lanl.gov).TheLosAlamosbranchoftheSeaborgInstitutewascharteredin1997,andathirdbranchwasestablishedatLawrenceBerkeleyNationalLaboratoryin1999.

ThepurposeoftheInstituteistoprovideafocusfortransactiniumscience,todevelopandmaintainUSpreeminenceintransactiniumscienceandtechnology,andtohelpprovideanadequatepoolofscientistsandengineerswithexpertiseintransactiniumscience.WithNNSA’srecentdesignationofLANLasa“plutoniumcenterofexcellence,”extensivecoordinationandleadershipintransactiniumscience,engineering,andmanufacturingareurgentlyneeded.TheLosAlamosbranchoftheSeaborgInstitutehasbeentaskedwithprovidingmuchofthiscoordinationandleadership.

Beginnings of the Seaborg InstituteTheLosAlamosSeaborgInstituteintegratesresearchprogramsonthechemical,physical,nuclear,andmetallurgicalpropertiesofthelight-actinideelements(i.e.,thoriumthroughcurium),withaspecialemphasisonplutonium,aswellastheirapplicationsinnuclearweapons,nuclearenergy,nuclearforensics,nuclearsafeguards,nuclear-wastemanagement,andenvironmentalstewardship.

TheInstituteprovidesauniquefocusandmechanismforcooperationandcollaborationamongthenationallaboratories,universities,andthenationalandinternationalactinide-sciencecommunity.TheInstitutefostersclosertieswiththeoutsidecommunityandtheworldthroughanextensivevisitorprogram,workshops,andconferences.Additionally,theInstituteencouragesgraduatestudents,postdoctoralcandidates,universityfaculty,andothercollaboratorstoperformresearchattheLaboratory.

TheLosAlamosSeaborgInstitutehasmanagedanddevelopedavarietyofLaboratoryprogramsandhasofferedscientificleadership,coordination,andmentoringformanyprogrammaticactivities.Afewrepresentativeexamplesarediscussedinthisarticle.

Plutonium Aging and the Enhanced Surveillance CampaignSinceshortlyafteritsestablishmentatLosAlamos,theSeaborgInstituteplayedacentralroleinplutonium-agingandpit-lifetimeassessments(seetheActinide Research Quarterly1stquarter2001).

20

15

10

5

0

Ave

rage

age

of w

arhe

ad (y

ears

) Total warheads in stockpileAverage age of warhead

1950 1960 1970 1980 1990 2000Year

The number of weapons in the stockpile is decreasing, and in another decade, the ages of most weapons will be well beyond their original design lifetimes.


intellectualcommunityinthediscussion,andtohelpestablishanofficialLANLpositionontheminimumpitlifetimebasedonsoundscientificunderstanding.Theseworkshopslaidthegroundworkforthejoint2006lifetimeassessmentsubmittedbythetwolabs.

Thepit-lifetimeassessmenthasbeenusedtomakenationalpolicydecisionsonpitreuse,pit-fabricationfacilities,andtheReliableReplacementWarhead.TheassessmentcontributedtoNNSA’sdecisiontoforegoconstructionofamodernpitfacilityanddesignateLosAlamosasthe“preferredalternative”formaintainingasmall-capacitypit-manufacturingcapability.

Plutonium Oxides and Disposition of Weapons-Usable PlutoniumBinaryactinideoxidessuchasPuO2areoftremendoustechnologicalimportancewith

widespreadapplicationasnuclearfuels,long-termstorageformsofsurplusweaponsmaterials,andpowergenerators(plutonium-238)forinterplanetaryexploration.Theyarealsoofgreatimportanceincorrosionreactions(uraniumandplutonium)innuclearweaponsandinthemigrationbehaviorofplutoniumintheenvironment.

Scientistswidelyheldthatoxidationofplutoniumtocompositionswithanatomicoxygentoplutoniumratiohigherthan2.0wasnotpossible.Therefore,PuO2becamethegenerallyacceptedchemicalformforlong-termstorageofexcessweaponsplutoniumandtheestablishedformofplutoniumintheenvironment.ThisbeliefwasshakenwhenLosAlamosscientistsreportedtheformationofPuO2.25throughthereactionofPuO2withwatervaporin2000.ThisreactionwasaccompaniedbyevolutionofH2gas,whichinitiatedintenseinterestsurroundinggasgenerationduringstorageandtransportofexcessweaponsplutonium.

TheLosAlamosSeaborgInstituteorganizedaseriesofworkshopstodiscussthestatusofthestructure,properties,andreactivityofPuO2andotheroxides.Subsequentworkshopsdiscussedhowthenewdataandastrongtechnicalunderstandingensurethesafeandproperstewardshipofactinideoxidematerials.Althoughoriginallycontroversial,theformationofPuO2+xisnowwidelyacceptedbytheinternationalactinide-sciencecommunity,anditsformationisincludedinmodernthermodynamicmodels.Thestructuralarrangementofatoms,theroleofimpuritiesingasgeneration,andtheroleofradiolysisarestillimportanttopicsunderstudytoday.AsummaryofimportantfindingsisdescribedintheActinide Research Quarterly2ndand3rdquarters2004.

Postdoctoral Fellows ProgramTheInstitute’sPostdoctoralFellowsProgramprovidesabroadintellectualcommunityforactinidescienceinsupportofLaboratorymissionsandcreatesamechanismtoattractandretainafuturegenerationofactinidescientistsandengineers.Theprogramalsofosterssustainedexcellenceandenhancedexternalvisibilityinactinidescience.

Seaborgpostdoctoralfellowsperformresearchthatsupportsnewactinidescienceatthesingle-investigatororsmall-teamlevelintheareasofactinidephysics,chemistry,metallurgy,sampleproduction,experimental-techniquedevelopment,theory,andmodeling.FundedbytheLaboratoryDirectedResearchandDevelopmentProgram,

An induction furnace that might be used to heat a pluto-nium alloy.


SeaborgpostdoctoralfellowsareselectedinahighlycompetitiveprocessandaresupportedhalftimebytheInstituteandhalftimebyprogramsupportprovidedbytheirmentors.

RecentSeaborgpostdoctoralfellowshaveconductedresearchinseveralLANLdivisions,includingMaterialsScienceandTechnology,EarthandEnvironmentalScience,Theoretical,Chemistry,NuclearMaterialsTechnology,andMaterialsPhysicsandApplications.Theirresearchhasincludedstudiesofelectroncorrelationsinneptunium,thesynthesisofactinideorganometalliccompounds(compoundswithmetal-carbonbonds),phasetransformationsandenergeticsinplutonium,covalencywithinf-elementcomplexes,radiation-damageeffectsinuranium-bearingdelta-phaseoxides,thermodynamicmeasurementsofactinides,andstructureandpropertyrelationshipsinactinideintermetallicalloys(alloyswithasuper-latticecrystalstructure,unlikeconventionalalloys).

Heavy Element Chemistry TheInstituteleadstheDOEOfficeofBasicEnergySciencesHeavyElementChemistryProgramatLosAlamos.Thecentralgoalofthisprogramistoadvancetheunderstandingoffundamentalstructureandbondinginactinidematerials.

Theactinideseriesmarkstheemergenceof5felectronsinthevalenceshell.Whetherthe5felectronsinactinidemolecules,compounds,metals,andsomealloysareinvolvedinbondinghasbeenthecentralandintegratingfocusforthefieldsofactinidechemistryandphysics.Inthepureelements,thosetotheleftofplutoniumintheperiodictablehavedelocalized(bonding)electronsandelementstotherightofplutoniumarelocalized(non-bonding).Plutoniumistrappedinthemiddle,andforthedelta-phasemetal,theelectronsareinanexoticstateofbeingneitherfullybondingnorlocalized,whichleadsto

novelelectronicinteractionsandunusualphysicalandchemicalbehavior.Theissuessurroundinglocalizedordelocalized5felectronspervadethebondingdescriptionsofmanyactinidemoleculesandcompounds,andthedegreetowhich5felectronsparticipateinchemicalbondinginmolecularcompoundsisunclear.Inthenormalnomenclatureofchemistry,thedelocalizedelectronsarethoseinvolvedincovalentbonding,whilethelocalizedelectronsgiverisetoionicbehavior.

The purpose of the Institute is to provide a focus for transactinium science, to develop and maintain US

preeminence in transactinium science and technology, and to help provide an adequate pool of scientists and

engineers with expertise in transactinium science.

These photos show a wide variability in color and general appearance for samples of plutonium dioxide. This variability in the appearance of plutonium dioxide samples is well known, and while the material is normally olive green, samples of yellow, buff, khaki, tan, slate, and black are also common. It is generally believed that the color is a function of chemical purity, stoichiometry, particle size, and method of purification.


TheLosAlamosapproachtounderstandingcovalencyandelectroncorrelationinactinidemoleculesandmaterialsistocombinesyntheticchemistry,sophisticatedspectroscopiccharacterization,andadvancedtheoryandmodelingtounderstandandpredictthechemicalandphysicalpropertiesofactinidematerials.ThismultidisciplinaryapproachisanestablishedstrengthatLosAlamosandprovidesthescientificmeanstoformulaterationalapproachestosolvecomplexactinideproblemsinawidevarietyofenvironments.

Nuclear EnergyPlutoniumisthelinchpinofanyfuturenuclear-energystrategy.Itisabyproductfrom“burning”uraniuminanuclearreactor.Next-generationnuclearfuelcyclesaredesignedtosafelyuseandrecyclenuclearfuelstoenhanceenergyrecoveryanddisposeofwastemoreefficiently.Safetyandwastemanagement,aswellasrobustsafeguardstolimitproliferation,areissuesthatwillbeaddressedinternationallytoenablelong-termsustainabilityofnuclearpower.Acombination

Seaborg points to the element 106, seaborgium, on the periodic table of the elements. He is the only person to have a chemical element named for him during his lifetime.

oftechnologiesiscurrentlybeingdevelopedtoachievetheselong-termgoals,andfurthereffortsarerequiredinfundamentalresearch,particularlyinthescientificfieldsrelatedtothelight-actinideelements,whichmakeupthefirsthalfoftheactinideseries.

TheSeaborgInstitutehasformallycontributedtothedevelopmentofnuclear-energyprogramsatLosAlamosandnationallysince2001.

The Future of Los Alamos as a Center of ExcellenceLosAlamoswillremainthecenterofexcellencefornuclear-weaponsdesignandengineeringaswellasplutoniumresearch,development,andmanufacturingunderNNSA’scomplextransformation.AsNNSA’sweapons-complextransformationreducesthesizeofthenuclear-weaponsprogram,theLaboratorymustmaintainthebreadthofcapabilitiesthatsupportstockpilestewardshipandnucleardeterrence.Atthesametime,LosAlamosmustalsoproduceinnovativediscoveriesthatwillleadtonewmissionsinplutoniumscienceandengineeringandprovidethecapabilitiestoaddressfuturetechnologicalchallenges.

Points of contact: David L. Clark, 505-665-6690, [email protected] Gordon D. Jarvinen, 505-665-0822, [email protected] Albert Migliori, 505-667-2515, [email protected]


Glenn T. SeaborgThe1930sandearly1940swereexcitingtimesontheUniversityofCalifornia’sBerkeleycampus.ErnestO.LawrenceandM.StanleyLivingstoninventedthecyclotrontherein1931,givingresearchersatoolwithwhichtobombardvariouselementswithintense,high-energybeamsofneutronsordeuteronsinordertoproducenuclearreactions.Beforethecyclotronwasinvented,onlyveryweakbeamsofsubatomicparticles—producedbynaturalsources,e.g.,radium—wereavailableforsuchresearch.

Thenuclearreactionsproducedbythecyclotron’sintensebeamsproducedmanynewelementsandisotopes.Nearlyallwereradioactive.

GlennT.Seaborgwasinspiredtoenterthenewfieldoftransuraniumelements—whosepurviewiselementsheavierthantheheaviestknownnaturalelement,uranium(atomicnumber92)—soonafterhearrivedatBerkeleyforgraduatestudiesandheardofEnricoFermi’s1934experimentsinRomeinwhichuraniumwasbombardedwithaweakbeamofhigh-energyneutrons.Fermi’sgroupthoughttheradioactiveproductsoftheseexperimentswereisotopesoftransuraniumelements,whichhadneverbeenseenbefore.In1939,OttoHahnandFritzStrassmanshowedthattheproductswereinfacttwoapproximatelyequal-sizednuclearfragments,certainlynottransuraniumelements.TheseGermanscientistsprovidedthefirstexperimentalevidencethatthesenuclearfragmentswereinsteadtheresultofnuclearfission—andreasontothinkanatomicbombcouldbebuilt.

SeaborgreceivedhisdoctorateinchemistryfromBerkeleyin1937atage25.Histhesisexperimentprovidedwhatwasprobablythefirstunequivocalevidencethatneutronscouldloseenergywhentheyscatteredfromatomicnuclei.RemainingatBerkeleyasGilbertLewis’laboratoryassistant,SeaborgcollaboratedwithphysicistsJackLivingoodandEmilioSegretodiscoverseveralradioactiveisotopesusedbyotherresearcherstoperformgroundbreakingbiologicalandmedicalstudiesshortlyafterthenewisotopeswerediscovered.

Meanwhile,Lawrencehadbeensteadilymakingbiggerandbiggercyclotronstoincreasetheirbeamenergy.Thefirstworkingcyclotron,whichproduced80-keVprotons,was4inchesindiameter.The60-inch-diametercyclotron,whichbeganroutineoperationinFebruary1939,produced16-MeVdeuterons.(Adeuteronconsistsofaprotonboundwithaneutron.)The60-inchcyclotronwasusedtomakethefirsttwotransuraniumelements—neptuniumandplutonium.

In1940,EdwinMcMillanandPhilipAbelsonbombardednaturaluranium—whichismostlyuranium-238—withneutronsfromthe60-inchBerkeleycyclotron.Oneproductoftheseexperimentswasanisotopewithatomicnumber93,atomicmass239,andahalf-lifeof2.5days(laterrevisedto2.356days).Whenanatomofuranium-238wasbombardedwiththecyclotron’sneutrons,itsometimesabsorbedoneofthemtobecomeuranium-239,whichthendecayed,withahalf-lifeof23.45minutes,byemittinganelectrontobecomethefirstknowntransuraniumelement.McMillannameditneptunium,becauseNeptuneisthenextplanetafterUranus,afterwhichuraniumhadbeennamed150yearsearlier.

McMillanthenbeganlookingforthedecayproductofneptunium-239.Accordingtocalculations,itwouldbeanisotopewithatomic

Seaborg and Segre present the one-half-microgram sample of plutonium to the Smithso-nian Institution in 1966.

A portrait of Seaborg in his laboratory at Berkeley.


This cigar box held a one-half-microgram sample of plutonium that Seaborg produced at Berkeley in 1941. Seaborg and Segre presented the sample and its carrier to the Smithsonian Institution.

number94andatomicmass239.Hedidn’tfindanything,soheassumed(correctly)thatthehalf-lifeofthedecayproducthesoughtmustbeverylong.Hopingtofindashort-livedisotopewithatomicnumber94,McMillanbeganbombardinguraniumwithdeuteronsfromthe60-inchcyclotroninsteadofneutrons.TheexperimentwascutshortwhenhewascalledtotheMassachusettsInstituteofTechnologytoworkonwartimeradar.

SeaborgcontinuedMcMillan’sexperiment,alongwithArthurC.Wahl,oneofSeaborg’stwograduatestudents,andJosephW.Kennedy,afellowBerkeleyinstructor.Theteamsoontentativelyidentifiedanisotopewithatomicnumber94,atomicmass238,andahalf-lifeofapproximately50years(laterrevisedto87.74 years),butfelttheydidn’thaveenoughprooftoannouncethediscoveryofanothernewelement.However,inanexperimentthatbeganthenightofFebruary23,1941,andranwellintothenextmorning,Wahlconfirmedthattheisotope’satomicnumberwasinfact94.Asecondtransuraniumelementhadbeenfound.

Thinkingthey’dreachedtheendoftheperiodictable(whichturnedouttobefalse),Seaborg’steamconsiderednamingthenewelement“extremium”or

“ultimium,”butthendecidedtofollowMcMillan’sleadandcallitplutonium,forPluto,whichatthetimewasthoughttobethenextplanetafterNeptune.Theychose“Pu”forthenewelement’ssymbol—foritsobviousolfactoryallusion—althoughthispranklatergotmuchlessofarisefromtheirfellowscientiststhantheyhadhoped.

Plutonium-238decaysbyemittingalphaparticles,whichareself-absorbedbytheplutonium-238andheatit,makingitanexcellentheatsource.Plutonium-238iscommonlyusedtoheatathermoelectricelement,whichconvertsheattoelectricityusedtopowerequipmentonboardspacecraft.Forexample,theelectricalequipmentonthetwoMarsRoversispowered

bythermoelectricgeneratorsheatedbyplutonium-238producedatLosAlamos.However,plutonium-238cannoteasilybemadetofissionandthereforecannotproducethenuclearchainreactionrequiredforapowerreactororabomb.

ButSeaborgandhisteamalsodiscoveredanotherplutoniumisotope.Neptunium-239decaysbyemittinganelectrontobecomeplutonium-239,whosehalf-lifeof24,100yearsexplainedMcMillan’sfailuretodetectit.Earlyin1941,Kennedy,Seaborg,Segre,andWahlfoundthatplutonium-239fissionswhenbombardedbyneutrons,likeuranium-235does.Thus,plutonium-239anduranium-235couldpotentiallybeusedtomakeatomicbombs.

Seaborg’steamsubmittedtheirresultstoPhysical ReviewattheendofMay1941.Becauseofthewareffort,however,thepaperwasnotpublisheduntil1946.

DuringWorldWarII,BerkeleygaveSeaborgaleaveofabsencefromhisjobasachemistryprofessortoworkattheUniver-sityofChicagoMetallurgicalLaboratory.Seaborgledthegroupofscientiststhatdevel-opedthechemicalextractionprocesstoproduceplutoniumfortheManhattanProject.TheManhattanProjectsecretly

producedenoughuranium-235andpluto-nium-239tomaketheworld’sfirstatomicbombs.

AfterWorldWarII,Seaborgcodiscoveredamericium,curium,berkelium,californium,einsteinium,fermium,mendelevium,nobelium,andseaborgium.Heistheonlypersonforwhomachemicalelementwasnamedduringhislifetime.McMillanandSeaborgsharedthe1951NobelPrizeinChemistryfordiscoveringthefirsttwotransuraniumelements.

Table of Contents

Weapons Programs Performance Snapshot 1Point of View— Strategic Weapons in the 21st Century: Hedging Against Uncertainty 3

Energy Balance in Fusion Hohlraums 6

Upgrades Made to the Trident Laser Facility 12

Fogbank: Lost Knowledge Regained 20The Los Alamos Branch of the Glenn T. Seaborg Institute for Transactinium Science 22

About the cover: Clockwise from left, Ray Gonzales replaces a flash lamp in the laser amplifier at the Trident Laser Facility. Gonzales adjusts a mirror on the front end of the Trident laser. A 5-ft-diameter vacuum vessel in the north target chamber is used for laser-matter interaction experiments. A graduate student, Sandrine Gaillard, checks laser and diagnostic alignment in the north target chamber before a 0.2-PW experiment. Photos: Robb Kramer, ADEPS

The Origin of the Z NumberNWJ Backward Glance

During the Manhattan Project, the US Army Corps of Engineers provided all support

services, including maintenance and utilities, for the laboratory and the townsite. In 1946, President Truman signed the Atomic Energy

Act, which established the Atomic Energy Commis-sion (AEC), a civilian agency. Under the terms of the 1946 act, the AEC was to be the “exclusive owner” of production facilities, but could let contracts to operate those facilities. At midnight on December 31, 1946, Manhattan Project assets transferred to the AEC. In 1947, the AEC began oversight of the Los Alamos Scientific Laboratory and the closed town of Los Alamos.

When the Zia Company was organized in April 1946 to assume support operations for Los Alamos, security was still very tight. Not only were badges required for all office and laboratory workers, but every resident, including children, needed a pass to get through the main gate (formerly a restaurant named Philomena’s and now De Colores on Route 502).

AEC officials decreed that employees of the new Zia Company would be given badge numbers with the

prefix “Z.” Until then, everyone had US Army security credentials. The protective force badge office slipped the letter Z and the number 00001 into its camera and the word went out to the Zia office for employees to report to the badge office and receive a new badge. When US Army numbers were dropped, other Los Alamos residents were given “Z” numbers too.

As the property management agent for the AEC, the Zia Company furnished plumbers and other craftsmen around the clock to repair furnaces, roof leaks, or whatever else might go wrong. Among other services, Zia workers installed clotheslines, planted trees, painted rooms, and changed light bulbs. In 1966, all residences were sold and then Los Alamos residents had to do their own maintenance or call commercial craftsmen.

Los Alamos National Laboratory still assigns Z numbers to employees. A “Z” number is a permanent employee number assigned to only one person. This number identifies the employee throughout his or her career at the Laboratory and is the same number even if the employee should return decades later.

The main gate as it appeared during the Manhattan Project. Inset, the location of the former main gate as it appears today.

Los Alamos National Laboratory, an affirmative action/equal opportunity employer, is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of the US Department of Energy under contract DE-AC52-06NA25396.

This publication was prepared as an account of work sponsored by an agency of the US Government. Neither Los Alamos National Security, LLC, the US Government nor any agency thereof, nor any of their employees make any warranty, express or implied, or assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed or represent that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by Los Alamos National Security, LLC, the US Government, or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of Los Alamos National Security, LLC, the US Government, or any agency thereof. Los Alamos National Laboratory strongly supports academic freedom and a researcher’s right to publish; as an institution, however, the Laboratory does not endorse the viewpoint of a publication or guarantee its technical correctness.

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