abstracts computational theoretical plasma physics

ABSTRACTS

Computational&TheoreticalPlasmaPhysics

AHybridModel forMultiscale LaserPlasma SimulationswithDetailed CollisionalPhysics

DavidBilyeu

RocketPropulsionDivision,AerospaceSystemsDirectorate,AirForceResearchLaboratory(AFRL/RQR),EdwardsAirForceBase,CA 93524

Program:AHybridModelforMultiscaleLaserPlasmaSimulationswithDetailedCollisionalPhysics(14RQ05COR)

ThispresentationreportsonrecentdevelopmentsinthefieldofLaserPlasmaInteraction(LPI)simulations.PriorworkfromAFRL/RQRSshowedthevalidityofourlevelgroupingtechniqueforcollisional‐radiative(CR)model,aone‐to‐onecomparisonofVlasov,PIC,andMulti‐Fluid solvers of a collisionless shock simulation, and ion acceleration due topondermotiveforcessolvedbytheMHDequations.WedemonstratedthattheBoltzmanngroupingtechniquewassuperiortotheuniformgroupingtechniqueforatomicHydrogen,andthatthismethodconservedenergytomachineprecision.Thecomparisonbetweenthethree solvers showed good agreement between PIC and Vlasov. The ion accelerationsimulationdemonstratedthattheMulti‐fluidequationswereadequatetocaptureelectronhydrodynamics. One of the key challenges associated with LPI simulations is the widerangeoflengthandtimescalesthatneedtoberesolved.Abruteforceattempttosolvetheassociated numerical simulation is not currently feasible so new algorithms must bedevelopedand tested.Thispresentationwill focuson recentdevelopments in expandingthe level grouping technique to new species, a new integration technique for the BGKintegrator, a spectral solver for the Vlasov equations, and a phase‐accurate multiscaleparticlepush.

DISTRIBUTIONA.Approvedforpublicrelease:distributionunlimited.PA#15584

SimulationforElectronImpactExcitation/DeexcitationandIonization/Recombination

RusselCaflisch†,BokaiYan†,Jean‐LucCambier‡

†DepartmentofMathematicsUniversityofCalifornia,LosAngeles(UCLA),LosAngeles,CA90095‡ComputationalMathematics,InformationandNetworksDivision,AirForceOfficeofScientificResearch,Arlington,VA22203

Program:KineticSimulationofNon‐EquilibriumPlasmas(FA9550‐14‐1‐0283)

We developed a kineticmodel and a correspondingMonte Carlo simulationmethod forexcitation/deexcitationandionization/recombinationbyelectronimpactinaplasmafreeof external fields. The atoms and ions in the plasma are represented by continuumdensities at a range of excitation levels and the electrons by an energy distributionfunction. A Boltzmann‐type equation is formulated and a corresponding H‐theorem isformallyderived.AMonteCarlomethodisdevelopedforanidealizedanalyticmodeloftheexcitationandionizationcollisioncrosssections.Thissystemsuffersfromtwodifficulties:alargenumberofinteractiontypeswithverylargevariationintheinteractionrates;andasingularityintherecombinationrateatsmallenergyfor(eitherof)theincomingelectrons.Toacceleratethesimulation,abinarysearchmethodisusedtoovercomethesingularratein the recombination process. Numerical results are presented to demonstrate theefficiencyofthemethodonspatiallyhomogeneousproblems.Theevolutionoftheelectrondistribution function and atomic states is studied, revealing thepossibilityunder certaincircumstances of system relaxation towards stationary states that are not equilibriumstates (i.e., not Gibbs distributions), due to non‐ergodic behavior. If ionization/recombinationisalsoincluded,thenthesystemgoestoequilibrium.

HybridVFPModelingofElectronTransportandRadiationGeneration

AlexanderThomas

NuclearEngineeringandRadiologicalSciencesDepartmentUniversityofMichigan,AnnArbor,MI48109‐2104

Program:HybridVFPModelingofElectronTransportandRadiationGeneration(FA9550‐14‐1‐0156)

Thephysicsofdense,ultrashort‐laserheatedplasmaisofinterestforanumberofrelatedapplications including ion acceleration, neutron production and inertia fusion energy. Inaddition,more recently the use of X‐ray FELs such as the LCLS are able to volume heatdensematerial.Tomodel these,wearedevelopingahybridVlasov‐Fokker‐Planck/ fluidcodewhichmodelsthetransportofenergeticelectronsindenseplasma.Herewereportonrecentdevelopmentsinthecode,includingtheinclusionofionizationandequationofstate

modelingforthebackgroundfluid,andanewpositivitypreservingspectralsolverfortheVlasov momentum space distribution that offers a number of benefits over othermomentumspaceadvectionschemes.WestudytheeffectofthenewphysicsmodelsinX‐ray heating experiments relevant to those on theMatter under Extreme Conditions endstationoftheLCLSlaser.

StudiesofPlasmaSheathPhysicsUsingContinuumKineticSimulationsofPlasmas

BhuvanaSrinivasan

AerospaceandOceanEngineeringVirginiaPolytechnicInstituteandStateUniversity,Blacksburg,VA24060

Program:StudiesofPlasmaSheathPhysicsUsingContinuumKineticSimulationsofPlasmas(FA9550‐15‐1‐0193)

Continuumkineticmodels of plasmaswill be developed to studyplasma sheathphysics.Foranyscenariowhereaplasmainteractswithasurface,suchasplasma‐wallinteractions,aplasmasheathformsattheinterface.Forhightemperatureplasmas,energeticelectronshave been known to cause secondary electron emissions from the wall. This can haveconsequencesfordevicessuchasHallthrustersaselectronemissionscanincreasetherateof erosion of the electrodes affecting the performance of the device. A study andunderstanding of secondary electron emissions and sheath stability can also have asignificant impactonotherapplicationswhereplasmascontactmaterial surfacessuchasplasma‐material interactiononsatellitesand instruments inspace,plasmaactuators,andother low‐temperatureplasmaapplications, tonamea few. Thedevelopment effortwillinvolve high‐order numerical methods such as the discontinuous Galerkin method todirectly solve the Vlasov‐Poisson and Vlasov‐Maxwell equations using an energy‐conservingalgorithmwiththecode,Gkeyll.

VariationalAlgorithmsforHigh‐FidelityPlasmaSimulations

StephenWebb,

RadiaSoft,LLC,Boulder,CO80304

Program:VariationalAlgorithmsforHigh‐FidelityPlasmaSimulations(YoungInvestigatorAward,FA9550‐15‐C‐0031)

Simulating plasma physics phenomena has traditionally been limited to a few plasmaoscillationsbecauseofnumericalheating in theplasma.This artificial heatingeventuallywashesoutphysicaleffects,makingtheresultsunreliable.Tomitigatethiseffectandstudybeam and plasma systems over many hundreds or thousands of oscillations, newalgorithmswhichprevent thisartificialheatingarerequired.Wewilldiscuss theconcept

behind so‐calledmultisymplectic or variational algorithms, and present results showingtheir exceptional long‐time stability. We will also discuss some details of theirimplementation,andfutureworkrequiredforplasmawakefieldacceleratorapplications.

Designofgraphene‐basedinterfacesforapplicationsinenergy,electronicsandphotonics

Ricky(LayKee)Ang

EngineeringProductDevelopmentNanyangTechnologicalUniversity(NTU),Singapore637457

Program:ModelingofUltrafastLaserInducedEmissionfromTIandGraphene(FA2386‐14‐1‐4020)

Inthispresentation,wewillpresentourrecentfindingsinrevisingsometraditionalscalinglaws inusingmonolayergraphene.The first topic is topresentanewscalingofelectronthermionic emission from graphene and its application as thermionic energy convertor(TIC).Itisfoundthatthatthetraditionalthermionicemissionlaw(Richard‐Dushmanlaw)is no longer valid for graphene, and a new thermionic emission law for graphene wasproposed, which agree with a recent independent experimental finding. This newthermionic emission model also suggests that traditional diode equation of a metal‐semiconductorcontactmaynotbevalid foragraphene‐semiconductorcontact.Usingthegraphene as cathodematerial, wewill show that an efficiency of about 45% at 900K ispossible. If the vacuum region between the electrodes is replaced with 2‐dimensionalmaterials based van der Waals hetero‐structures, the performance can be improved tooperate at 400K with an efficient from about 10% to 20%, which is unmatched incomparison to thebestTEmaterialsatZT=1 to4.Thesecond topic is toshowthat theplasmonic mode for graphene is different from metals, for which the excitation of thegraphene plasmonicmodel can be realized at amuch lower excitation energy at longerwavelength. This finding can be useful for create compact coherent radiation source atlongerwavelength.

KEENandKEEPNWaveSimulationsUsingtheVlasov‐PoissonModelEquations

BedrosAfeyan

PolymathResearchInc.Pleasanton,CA94566

Program:KEENWavesandtheirInteractionswithGeneralizationstoMultispeciesPlasmas,RelativisticDynamics,CollisionalityandMultidimensionality(FA9550‐15‐1‐0271)

Weshowforwell‐drivenKEEN(KineticElectrostaticElectronNonlinear)wavesandtheiranalogsinpairplasmasKEEPN(Positron)waves,howthedynamicsiscapturedinavariety

of complimentary numerical approaches. Symplectic integration and quadrature nodebasedtechniquesaredeployedtoachievesatisfactoryresultsinthelongtimeevolutionofhighly nonlinear, kinetic, non‐stationary, self‐organized structures in phase space. Fixedandcompositevelocitygridarbitrary‐orderinterpolationapproacheshaveadvantageswehighlight. Adaptivity to local phase space density morphological structures will bediscussed startingwithin the framework of the ShapeFunctionKinetics (SFK) approach.Fine resolution in velocity only in the range affected by KEEN waves makes for moreefficientsimulations,especially inhigherdimensions.Weexplore theparameterspaceofunequalelectronandpositrontemperaturesaswellastheeffectsofarelativedriftvelocityin their initial conditions. Ponderomotively driven KEEPN waves have many noveltieswhen compared to KEENwaves, such as double, staggered, vortex structures,whichwehighlight.

HighPowerElectromagneticSources

HighPowerRecirculatingPlanarAmplifiers

RonaldM.Gilgenbach†,Y.Y.Lau†,NicholasJordan†,DavidChernin†,StevenExelby†,GeoffGreening†,BradHoff‡,DavidSimon†,PatrickWong†,PengZhang†

†NuclearEngineeringandRadiologicalSciencesDepartmentUniversityofMichigan,AnnArbor,MI48109‐2104‡HighPowerElectromagneticsDivision,DirectedEnergyDirectorate,AirForceResearchLaboratory(AFRL/RDH),KirtlandAFB,NM87117

Program:HighPowerRecirculatingPlanarAmplifiers(FA9550‐15‐1‐0097)

ExperimentsandtheoryatUMaredirected towards thegoalofextending thesuccessful,RecirculatingPlanarMagnetronRPMoscillator(upto150MW)totheamplifierregimeat10’sto100MW[1].ExperimentsaredrivenbytheMELBAgeneratoratparameters‐300kV, 1‐10 kA with pulselengths up to 0.5 microsecond. The RF driver for amplifierexperimentswillbeaconventional3‐GHz,2.6MWmagnetronoperatedat48kVand110Awith a pulselength of 5 microseconds. Initial amplifier designs and simulations will bepresented.

UMcollaborationswithAirForceResearchLabarebeingconductedonacoaxialall‐cavityextractor CACE‐RPM. Another AFRL collaboration is UM testing of a recirculating planarmagnetronproducedbyadditivemanufacturing(3‐Dprinting).

Theory research concerns Brillouin flow, which is the prevalent flow in crossed‐fielddevices. We systematically study its stability in the conventional, planar, and invertedmagnetron geometry.We find that theBrillouin flow in the invertedmagnetron ismoreunstablethanthatinaplanarmagnetron,whichinturnismoreunstablethanthatinthe

conventional magnetron [2]. Thus, oscillations in the inverted magnetron and planarmagnetronmay startup faster than the conventionalmagnetron. This is consistent withsimulation studies, and with the negative mass property in the inverted magnetronconfiguration.Alsoexaminedistheabsoluteinstabilityatthebandedgesforabeamthatexhibitspositiveornegativemassbehavior[3].

[1]R.M.Gilgenbach,Y.Y.Lau,D.M.French,B.W.Hoff,J.Luginsland,andM.Franzi,“CrossedFieldDevice,”U.S.PatentUS8,841,867B2,Sept.23,2014.[2] D. H. Simon, Y. Y. Lau, G. Greening, P.Wong, B.W. Hoff, and R.M. Gilgenbach,Phys.Plasmas22,082104(2015).[3]D.M.H.Hung,I.M.Rittersdorf,P.Zhang,D.Chernin,Y.Y.Lau,T.M.Antonsen,Jr.,J.W.Luginsland,D.H.Simon,andR.M.Gilgenbach,Phys.Rev.Lett.115,124801(2015).

PhysicsofGW‐classHighPowerMicrowaveAmplifiers

PeterJ.Mardahl,BradW.Hoff

HighPowerElectromagneticsDivision,DirectedEnergyDirectorate,AirForceResearchLaboratory(AFRL/RDH),KirtlandAFB,NM87117

Program:PhysicsofGW‐classHighPowerMicrowaveAmplifiers(13RD04COR)

(PublicReleaseforAbstractPending)

OvermodedCircuitsforHighPowerTravelingWaveTubesandKlystrons

JasonHummelt,MichaelShapiro,RichardTemkin

PlasmaScienceandFusionCenterMassachusettsInstituteofTechnology(MIT),Cambridge,MA02139

Program:VolumeModeTravelingWaveTubeAmplifier(FA9550‐15‐1‐0058)

There is great interest in extending the operating frequency of traveling wave tubes(TWTs)andklystronsintothe100to1000GHzfrequencyrangeatpowerlevelsinthetensof watts to kilowatts. We are exploring the use of overmoded interaction structures toprovidethedesiredperformanceindevicesthatcanbebuiltusingpresent‐daytechnology.In a first set of experiments, we have demonstrated an overmoded TWT at W‐Band.Operatingatavoltageof30.6kVwith250mAofcollectorcurrent,theTWTwaszero‐drivestableandachieved21±2dBlineardevicegainwith27Wpeakoutputpower.Forthenextphaseofthisresearch,weareconsideringtheuseofaPhotonicBandgap(PBG)structuretocreateaslowwavestructurewithanoversizedbeamtunnel.Theincreaseinbeamtunneldiameterwill allow either a dramatic increase in device power or an increase in devicefrequencyatconstantbeampower.ThePBGstructurehastheadvantageofconfiningonlytheselectedmodewhileallowingunwantedmodestodiffractoutofthestructure.

HighPowerMicrowave/TerahertzGenerationfromSuperconductorAntennasforMilitaryApplications

TimothyJ.Haugan†,WilkinW.Tang‡

†PowerandControlDivision,AerospaceSystemsDirectorate,AirForceResearchLaboratory(AFRL/RQQ),WrightPattersonAirForceBase,OH45433‡HighPowerElectromagneticsDivision,DirectedEnergyDirectorate,AirForceResearchLaboratory(AFRL/RDH),KirtlandAFB,NM87117

Program:HighPowerMicrowave/TerahertzGenerationfromSuperconductorAntennasforMilitaryApplications(15RQCOR215)


FieldEmissionCathodeResearch

DonShiffler1,WilkinTang1,JenniferElle2,KevinJensen3,JohnHarris4

1HighPowerElectromagneticsDivision,DirectedEnergyDirectorate,AirForceResearchLaboratory(AFRL/RDH),KirtlandAFB,NM871172HighPowerElectromagneticsDivision,DirectedEnergyDirectorate,AirForceResearchLaboratory(AFRL/RDH),NationalResearchCouncilFellow,KirtlandAFB,NM871173NavalResearchLaboratory,Washington,DC203754NavalResearchLaboratory,NavalReserveOffice,Washington,DC20375

Program:CathodeMaterialsResearchforHighPowerMicrowaveSources(14RD04COR)


CarbonNanotubeFiberFieldEmissionCathodes

StevenFairchild1,NathanielLockwood2,MatteoPasquali3

1FunctionalMaterialsDivision,Materials&ManufacturingDirectorate,AirForceResearchLaboratory(AFRL/RXA),WrightPattersonAFB,OH454332HighPowerElectromagneticsDivision,DirectedEnergyDirectorate,AirForceResearchLaboratory(AFRL/RDH),NationalResearchCouncilFellow,KirtlandAFB,NM871173DepartmentofChemicalandBiomolecularEngineeringandDepartmentofChemistryRiceUniversity,Houston,TX77005

Program:InvestigationofNovelNanomaterials(12RX17COR)

Fieldemission(FE)cathodesmadefromcarbonnanotube(CNT)fibershavedemonstratedhighemissioncurrents,lowturn‐onvoltages,longlifetimesandofferconsiderablepotentialforuseaselectronsourcesforvacuumelectronicdevices.CNTfibers

werefabricatedbywet‐spinningofpre‐madeCNTs1andconsistofCNTfibrilsheldtogetherbyvanderWaalsforces.Thefiberswere10‐100 mindiameterandtheirmorphologywascontrolledbyfabricationmethod,processingconditions,aswellaspurity,size,andtypeoftheCNTstartingmaterial.Thermalandelectricalconductivitywasmeasuredwiththe3‐omegamethod,andfiberdensitywasdeterminedwithtransmissionelectronmicroscopy.Wideanglex‐raydiffractionwasusedtomeasurefiberalignment.Fiberswiththehighestdensity,alignment,thermalandelectricalconductivityhadthebestfieldemissionperformance.Recentresultshavedemonstratedasingle5mmlongfiberwitha20 mdiameteremitting5.2mAbeforefailure,and6.1mAwhentreatedwithBoronNitride2.Residualgasanalysis(RGA)wasusedtoidentifythespeciesdesorbedduringfieldemissionandmodelwasdevelopedforthetransitionfromadsorbate‐enhancedFEatlowbiastoFEfrompureCNTsathighbias3.InfraredimagesofCNTfibersduringFEhavebeencapturedwithanInGaAsarraycamera,showingtemperaturesof~600°Cwhileemittingcurrentsof~4mA.MechanismsoffiberheatingduringFE,toincludeJouleandNottinghameffects,wereinvestigated.Calculatedthermalperformancebasedonmeasuredthermalconductivityispresented,andcomparisonsbetweenobservedandcalculatedthermalperformancearediscussed.

1.N.Behabtuetal.,“Strong,Light,MultifunctionalFibersofCarbonNanotubeswithUltrahighConductivity,Science2013,339,182.2.RajibPauletal.,“Microwave‐AssistedSurfaceSynthesisofaBoron–Carbon–NitrogenFoamanditsDesorptionEnthalpy”AdvancedFunct.ionalMaterials,2012,22,3682–36903.P.T.Murrayetal.,“Evidenceforadsorbate‐enhancedfieldemissionfromcarbonnanotubefibers”AppliedPhysicsLetters,103,053113(2013)

*WorksupportedbyaGovernmentAgency

CaseNumber:88ABW‐2014‐1386;MaterialwasassignedaclearanceofCLEAREDon03Apr2014

Phase‐ControlledMagnetronDevelopment

JimBrowning

DepartmentofElectricalandComputerEngineeringBoiseStateUniversity,Boise,ID83725

Program:Phase‐ControlledMagnetronDevelopment(AwardPending)

Simulations (2D) of a Rising Sunmagnetron using the code VSIM have shown that it ispossibletoactivelycontroltheRFphaseofamagnetronbymodulatingtheelectronsourceattheoscillatingfrequency(f)oranoddsub‐harmonic(f/3).Theconceptusesaspatiallyaddressable cathode that allows electron injection at locations and timing to control thestartupandlocationoftheelectronspokesand,hence,theRFphase. Simulationhasalso

shown that only 10% of the total injected current must be modulated to dynamicallycontrol the phase. In our new research we plan to build a magnetron using a facetedcathode that contains Gated Field Emission Arrays (GFEAs) to provide the addressable,modulatedelectronsource.ThefacetplatesuseelectronhopfunnelsthatallowtheGFEAstobeplacedonthebacksideoftheplateoutofthemagnetroninteractionspace.Electronsare injected into the interaction space through slits in the plates, so the GFEAs areprotected.Themagnetronexperimentwillusethecircuitofacommerciallyavailable915MHz magnetron which will be placed inside a vacuum test chamber. We also plan tosimulate this new magnetron experiment in 3D. Simulation results demonstrating thephase control concept along with design plans for the magnetron experiment will bepresented.

FundamentalProcessesandInteractionsinPlasmas

UnderstandingIntenseLaserInteractionswithSolidDensityPlasma*

AlexanderThomas


Program:UnderstandingIntenseLaserInteractionswithSolidDensityPlasma(FA9550‐12‐1‐0310)

*reassignedfromEnergyTransportinSolidssessionduetologisticalconsiderations.

Herewe show that inultrafast laser interactionswitha free flowingheavywater target,significant fusionneutronproductioncanoccur.Neutronshavenumerousapplications indiverse areas, such as medicine, security, andmaterial science. For example, sources ofMeV neutrons may be used for active interrogation for nuclear security applications.Ultrashort laserpulse interactionswithdenseplasmahaveattractedsignificantattentionascompact,pulsedsourcesofneutrons.Togenerateneutronsusingalaserthroughfusionreactions,thinsoliddensitytargetshavebeenusedinapitcher‐catcherarrangement,usingdeuterated plastic for example. However, the use of solid targets is limited for high‐repetitionrateoperationduetotheneedtorefreshthetargetforeverylasershot.Usingafreeflowing10micronscalediameterdeuteratedwatertargetandthehighrepetitionrate(500Hz)Lambda‐cubed lasersystemat theUniv.ofMichigan(12mJ,800nm,35fs), D‐Dfusion reactions occur generating 2.45 MeV neutrons. Under best conditions, a timeaverage of ~10^5 neutrons / s are generated. We also find the scaling of the neutrongenerationwithlaserpower.

CharacterizingHypervelocityImpactPlasmasandEffectsonSpacecraftwithParticle‐In‐Cell(PIC)

SigridClose†,AlexFletcher‡,

†DepartmentofAeronauticsandAstronauticsStanfordUniversity,Stanford,CA94305‡MassachusettsInstituteofTechnology(MIT,Cambridge,MA02139)&CenterforSpacePhysics,BostonUniversity(Boston,MA02215)Program:CharacterizingHypervelocityImpactPlasmasandEffectsonSpacecraftwithParticle‐in‐Cell(FA9550‐14‐1‐0290)

When a hypervelocity particle, such as ameteoroid or piece of orbital debris, impacts aspacecraft,afractionofitsincomingenergyisconvertedintoionization.Thisresultsinawarm, dense plasma that expands into the vacuum. In order to understand the plasmagenerated by a hypervelocity particle, we have developed smoothed particlehydrodynamics(SPD)anddiscontinuousGalerkin(DG)particle‐in‐cell(PIC)techniquestomodel theshockandresultingplasma.The impact‐producedplasmais inaregimecalledwarmdensematter (or equivalently, non‐ideal plasmaor strongly coupledplasma). It isdifficulttotreattheoretically,sincethenon‐idealityalterstheequationofstate,reducestheenergytransferratebetweenionsandelectrons,andmostcritically, increasesthechargestate by depressing ionization potentials. Both SPD andDG can treat this unique regimeandcanbecombinedtogivethefirstparametersofhypervelocityimpactplasma.

RecentlywehavecomputedbothplasmadensityandtemperatureasafunctionoftimeanddistancefromtheimpactpointandshownthatthetemperatureisontheorderofafeweV,whichisanorderofmagnitudesmallerthanpredicted.Thisresultagreeswithrecentdatafromourexperimentalcampaign.Theresultsalsoshowaminimumvelocity thresholdof18 km/s for fully ionized plasma production, which matches the velocity threshold forradio frequency (RF) measurements from impact experiments detected using patchantennas.Furthermore,thefullyionizedplasmaproduceselectrostaticoscillationsthatcancouple to anelectromagneticwave thatpropagatesaway from theplasma.These resultsarehighlydependentuponthemassandvelocityof the impactor,aswellas theangleofincidenceandtargettype.Highvelocityparticles impactingontungstenproduceplasmaswiththehighestdensityandpotentialforRFemission.

EnergyFlowinDenseOff‐EquilibriumPlasma

SethPutterman

DepartmentofPhysicsandAstronomyUniversityofCalifornia,LosAngeles(UCLA),LosAngeles,CA90095http://acoustics‐research.physics.ucla.edu/

Program:EnergyFlowinDenseOff‐EquilibriumPlasmas(FA9550‐12‐1‐0062)

Nature likes to formdenseplasmas!When energy is injected into a dense gas, a plasmawithanunexpectedlyhighfreechargedensityiscreated.ThechargedensityisthousandsoftimesgreaterthanwouldfollowfromapplicationofSaha’sequationof ionization.Thisphenomenon has been observed in laser breakdown, spark discharges and inside of acollapsingbubble.Thechargedensitiesoftheseplasmasissolargethattheyareopaque.Forinstanceasparkdischargeinadensegascanblocklightfromapowerfullaseroverarangeofwavelengthsgreaterthan500nm.Onthenanosecondtimescalewehaveobserveda limiting of the energy density which is similar to luminosity saturation in nuclearexplosions. For the spark and collapsing bubble ns energy transport is dominated byscreened binary collisions. On the picosecond time scale we observe for hydrogen astationary contact discontinuitywhich is interpreted in terms of a 25000K electron gasserving as the charge compensating background for cold charged ions with a plasmaparameterof70.AccordingtoTellersuchawarmdenseplasmahasformedacondensedphase.Thepresenceofthecondensate,enhancesandstabilizestheoff‐equilibriumstatesothatenergytransferisnolongercharacterizedbyscreenedbinarycollisions,butinsteadisdominatedbyelectron‐phonon[i.e.particlewave]interactions.Weproposethatthisnewregime for plasma physics will enjoy applications and that an elucidation of the newtransportprocesseswillbekeytorealizingnewdevices.

SpectroscopicAnalysisofEnergyDistributioninLowTemperaturePlasmasforAFApplications

StevenF.Adams

PowerandControlDivision,AerospaceSystemsDirectorate,AirForceResearchLaboratory(AFRL/RQQ),WrightPattersonAirForceBase,OH45433

Program:ElectronEnergyDistributionandTransferPhenomenainNon‐EquilibriumGases(13RQ13COR)

This presentation reviews the FY15 results of the AFOSR in‐house laboratory task,LRIR#13RQ13COR. The task consists of research to apply advanced spectroscopictechniques tomeasure,monitor andultimately control the distribution of electronic andkinetic energies within low temperature plasmas and enhance the understanding of

phenomena associated with non‐equilibrium energy distributions. This effort supportsdevelopments in areas of interest to the Air Force such as plasma switching, ignitionenhancement, laser medium excitation and plasma surface treatments. Since standardkineticmodelingistypicallynotapplicabletoanionizedgas,accuratecomputationsmustrepresent the energy dependent behavior of all charged and neutral species in the non‐equilibrium environment. The primary objective of this task has been to analyze thekinetics and resulting chemistry of radicals, ions and electrons within laboratory scaleplasma systems. Achievements during FY15 includemeasurement of temperatures andenergy distributions within micro‐discharges, the study of the secondary ionizationcoefficientindcbreakdownviaPaschencurveanalysis,theinvestigationofionchemistryleading to ignition of advanced fuel molecules and the investigation of multi‐photonabsorptionand ionization techniques forbothdiagnostics andpre‐ionization seeding forgas breakdown. Experimental approaches were to apply advanced spectroscopictechniques, includingmethods in subtractive triple‐grating spectroscopy, laser scatteringtechniques,opticalemissionspectroscopyandmulti‐photonlasertechniquestolaboratorygas systems. Advanced spectroscopic analyses have determined fundamental rateconstants,processkineticsandenergydistributionsofnon‐equilibriumgases.DuringFY15,four journal papers have been published from this task along with four more journalmanuscriptssubmitted.

DISTRIBUTIONA.Approvedforpublicrelease:distributionunlimited.Case#88ABW‐2015‐4704

Non‐equilibriumkineticsinhighpressuregasmixtureplasmas

JamesScofield

PowerandControlDivision,AerospaceSystemsDirectorate,AirForceResearchLaboratory(AFRL/RQQ),WrightPattersonAirForceBase,OH45433

Program:Non‐equilibriumkineticsinhighpressuregasmixtureplasmas(13RQ09COR)


FundamentalStudiesofAtmosphericPressure,NanosecondPulsedMicroplasmaJets

ChunqiJiang1,2,JamieL.Lane1,ShutongSong1,2,JohannaNeuber1,2,MartinA.Gundersen3,AndrasKuthi3

1FrankReidyResearchCenterforBioelectricsOldDominionUniversity,Norfolk,VA23508USA2DepartmentofElectricalandComputerEngineeringOldDominionUniversity,Norfolk,VA23529USA3DepartmentofElectricalEngineering–ElectrophysicsUniveristyofSouthernCalifornia,LosAngeles,CA90089,USA

Program:FundamentalStudiesofTransient,Atmospheric‐Pressure,Small‐ScalePlasmas(FA9550‐11‐1‐0190)

Nanosecondpulsedmicroplasma jets are highly non‐equilibriumplasmas propagating inambientairandwithatleastonedimensionslessthan1mm.Theypromiseabroadrangeof applications including surface decontamination, air purification, infectious diseasecontrolandplasmaignitionforcombustion.Dynamicsofthemicroplasmajetspoweredbynanosecondvoltagepulseswas studiedwithhigh‐speed imagingaswell as spatially andtemporallyresolvedopticalemissionspectroscopy.Shorterpulseswithshorterrisetimesallowedhigher energydeposition into theplasmaandpromote rapid accelerationof theionizationwavefronts; 4 times higher of thewavefront velocitywas observed for a 5 nspulsedplasmastreamercomparedwiththatbythe164nspulsedexcitation.Microplasmajets powered by shorter (e.g. 5 ns) voltage pulses enhanced the production of excitedatomic oxygen at the same rotational and vibrational temperatures (300 K and 3000 K,respectively) compared with the microplasma driven by >140 ns pulses at the samevoltage. In addition, two‐photon absorption laser induced fluorescence spectroscopyresolveda1‐mmHe/(1%)O2plasmajetproducingatomicoxygendensityontheorderof1013cm‐3.AbsolutemeasurementsofOHdensityfortheplasmajetareinprogressusingthecavityring‐downtechnique.________________________________

*WorkalsosupportedbytheAirForceOfficeofScientificResearch(AFOSRAwardNo.FA9550‐11‐1‐0190,FA2386‐14‐1‐3006(DURIP)).

PonderomotivelyDrivenQuasi‐Free‐SpaceElectronSeriesResonancePlasmas

BradW.Hoff,RemingtonR.Reid


Program:PonderomotivelyDrivenQuasi‐Free‐SpaceElectronSeriesResonancePlasmas(13RD02COR)

(PublicReleaseforAbstractPending).

ThreatDetectionUsingaModularCosmicRayMuonTomographySystem

JamesL.Popp,KevinR.Lynch

EarthandPhysicalSciencesDepartmentYorkCollege,TheCityUniversityofNewYork,Jamaica,NY11451

Program:ThreatDetectionUsingaModularCosmicRayMuonTomographySystem(FA9550‐15‐1‐0048)

Wewill leverage recentdevelopments in computingandelectronics todevelopa simple,effective, robust,modular threatassessmentsystemtodetectcontrabandusingnaturallyoccurringcosmicraymuons.Wewillbuildthissystemusingthecoretechnologiesofsingleboardcomputers,scintillatingplasticsheet,andgaseouselectronmultipliers.Wewillusethis “LEGO” –like system to demonstrate simple tomography of brick‐size mock threatswithin 55 gallon‐drum scale targets. By using commercial, off‐the‐shelf techniques andcomponents,wesimplifyconstructionandreducecostscomparedtodesigningsignificantcustom equipment.We aim to build a systemwhere deployment should be possible bytrained,butnot expert, personnel.Wewill demonstrate the robustnessof the systembycollectingdatainavarietyofoutdoorconditionsforanextendedperiod.

During the course of this research, we will: 1) Build a suite of detectors. 2) Constructmodular,weathertightmodulesforthesedetectors.3)Demonstratesimpletomographyofsmalldensethreatsin55gallondrum‐scalecontainers.4)Usethedesignandconstructionprocess to drive student development and education. 5) Perform detailed studies of thereal‐world backgrounds important for this screening method and their dependence onfactorsincludingterrestrialandsolarsources.

PlasmaandLaserKineticswithinaDischargeAssistedNobleGasLaser

GregPitz†,NathanielLockwood‡

†LaserDivision,DirectedEnergyDirectorate,AirForceResearchLaboratory(AFRL/RDL),KirtlandAFB,NM87117‡HighPowerElectromagneticsDivision,DirectedEnergyDirectorate,AirForceResearchLaboratory(AFRL/RDH),KirtlandAFB,NM87117

Program:PlasmaandLaserKineticswithinaDischargeAssistedNobleGasLaser(14RD03COR)

TheAdvancedNobleGasLaser(ANGL)usesamildRFdischargetoexciteargon(Ar)atomsfromthegroundstate(s0)tothemetastables5state,allowingArtobeopticallypumped(s5 – p9) as a quasi‐three level laser similar to the Diode Pumped Alkali Laser (DPAL).Helium(He)collisionalmixingfromthep9tothep10stateallowslasingfromp10tos5at912 nm. Previously, 2mW of average output power has been achieved at the Air ForceResearchLaboratory(AFRL)usinga811nmpulsedTitanium:Sapphire(Ti:Sapph)lasertopumpaplasmadischargetubewitha1‐10%Ar:Hemixture.Recently,numberdensityandgain diagnostics have been conducted in a parallel‐plate discharge configuration. Thisarchitecture will also be used in demonstrating the world’s first continuous wave (cw)diode‐pumpedANGL.

Dr. Pitz is a research physicist at Air Force Research Lab in Albuquerque, New Mexicowhereheleadsateamdevelopingtheworld’sfirstopen‐cycleflowingdiodepumpedalkalilaser.Dr.Pitzhasmadenumerouscontributionstoatomicspectroscopyofalkaliatoms,thedevelopmentofhybrid lasers, andmodelingof innovativenewdesigns.Hehasproducednumerous publications on DPALs and their applications, including broadening and highpressurelineshapeoftheD1andD2lines.In2013,hewasawardedthePresidentialEarlyCareer Award for Scientists and Engineers by President Obama for his contributions toDPAL research along with his leadership in the field and active participation in STEMoutreachprograms.HehasmostrecentlyservedinWashington,D.C.,developingpolicytobetterintegrateAirForceoperatorsintothedevelopmentplanningprocess.

DISTRIBUTIONA.Approvedforpublicrelease:distributionunlimited.Case#377ABW‐2015‐0642

EnergyTransportinSolids

ElectronDynamicsDuringHigh‐Power,Short‐PulsedLaserInteractionswithSolidsandInterfaces

PatrickE.Hopkins

MechanicalandAerospaceEngineeringDepartmentUniversityofVirginia,Charlottesville,VA22904‐4746

Program:ElectronDynamicsDuringHigh‐Power,Short‐PulsedLaserInteractions(FA9550‐13‐1‐0067)

This objective of this Young Investigator Program is to explore the effects of spatially‐confined ultrafast optical excitations of materials to a state of strong electron‐phononnonequilibriumontheevolutionofdepositedenergy,electronicscatteringprocessesandstructuraltransformationsdrivingmaterialprocessingandmanipulationwithhigh‐powerpulsed lasers and/or applied electric fields. Through variousmeasurements of thermalproperties of thin film metals and non‐metals using pump‐probe thermoreflectancespectroscopywithsub‐picosecondtemporalresolution,wedemonstratetheroleofexcitedelectrons and/or externally applied fields on heat transfer mechanisms and resultingnanoscalestructuralpropertiesofthematerials.Notably,wedemonstratethestrongroleofnanoscale interfacesonhotelectronrelaxationthroughmeasurementsof theelectron‐phonon coupling factor in thin gold with and without adhesion layers on varioussubstrates.Weobservethatthecouplingbetweentheelectronicandthevibrationalstatesis increasedbymore than five‐foldwith the inclusionof a~3nmTi adhesion layer thatstrengthens the interfacial bonding. Furthermore, we show that the electron‐phononcouplingincompositemetalfilmsonthermallyinsulatingsubstratesdonotplayaroleinsteadystatelaserdamage,andthatthisdamagemechanismsisdrivenbyheatingthemetal

film to above the melting threshold from the accumulation of laser pulse energy. Inaddition,wedemonstratetheabilitytocontrolthethermalconductivityinthinfilmswithappliedelectric fieldbymanipulating internal interfaces. Weexperimentallyshowactiveandreversible tuningof thermalconductivitybymanipulating thenanoscale ferroelastic

domainstructureofalead‐zirconatetitanatefilmwithappliedelectricfields.

DynamicsofHigh‐IntensityLaser‐DrivenProtonBeamTransportinSolidDensityMaterials

ChristopherMcguffey

MechanicalandAerospaceEngineeringDepartmentUniversityofCalifornia,SanDiego,CA92093‐0411

Program:DynamicsofHigh‐IntensityLaser‐DrivenProtonBeamTransportinSolidDensityMaterials(FA9550‐14‐1‐0346)

Whenextraordinarilyintenseparticlebeams,madepossiblewithshort‐pulselasers,entermatter, complex dynamics apply including the matter's response to the intense beam(heating, ionization, strongreturncurrents, current‐driven fields)and in turn thebeam'sresponse to the matter (temperature‐ and ionization state‐ dependent stopping, fieldeffects).Toinvestigatethefundamentaldynamicsathand,wehaveusedahybridparticle‐in‐cellcodeandexperimentaldatafromworld‐classshort‐pulselasers.Inthefirstyearofthe projectwe have explored options to improve the stopping powermodel used in thesimulations,conductedseriesofsimulationstoquantifyprotonrangeasafunctionofbeamflux indifferentmaterials,andmodeledbeamtransportthroughsolids forcomparisontoexperimental data. Our simulations have demonstrated that intense proton beams canexhibit departure fromcold stoppingpowerbehavior (J.Kim,PRL, 2015). For extremelyintenseandfocusedbeams,thedepositionprofilecanbecompletelydifferent inboththelongitudinal and transverse target dimensions due to target heating effects and self‐generatedfields,respectively.AmongtheinterestingresultsbeyondthePRL,wefindthatfor extremely high current density beams, the heating due to Ohmic drag of the returncurrents can become comparable to the energy rate deposited by the beam itself, and amulti‐picosecondintensebeamwilldepositmuchdeeperintoatargetthanashorterbeamofthesameenergyorintensity.

NonlinearDielectricsforCompactPulsedPower&HPMProtection

SusanHeidger,BradHoff,ReneeVanGinHoven,AndrewGreenwood,DavidFrench


Program:NonlinearDielectricsforCompactPulsedPower&HighPowerMicrowaveProtection(12DO02COR)


RFGenerationBasedonNonlinearTransmissionLines

JoseRossi

AssociatedPlasmaLaboratoryNationalInstituteforSpaceResearch(InstitutoNacionaldePesquisasEspaciais,INPE)SãoPaulo,Brazil

Program:StudyofHVDielectricsforHighFrequencyOperationinTransmissionLines(FA9550‐14‐1‐0133)

Nonlineartransmissionlines(NLTLs)providesaningenuouswayofgeneratingRFwithoutusing vacuum tubes. Their main envisaged applications are in RF sources in battlefieldcommunication disruption, carrier waves in telemetry systems of space vehicles,transmittersofpulsedradarsforremotesensing,etc.IntheRFfrequencyrangeupto400MHz,adispersivelumpedNLTLbasedonnonlinearelements(ferriteinductorsorceramiccapacitors) is used. Above 400 MHz, a configuration using a loaded coaxial line withexternalmagneticbias(knownasgyromagneticNLTL)hasshownbetterperformance.Thegoal of this presentation is to describe the research on lumped capacitive NLTLs andgyromagnetic lines developed so far at Plasma Laboratory from INPE. In this work, aslumpedcapacitiveNLTLsemploynonlineardielectricmediums,ceramicdielectricsbasedonleadzirconatetitanate(PZT)andbariumtitanate(BT)werecharacterized.Toassesstheperformanceofthesedielectrics,HVPZTandBTNLTLswerebuiltandtested,achievingRFgeneration at 100MHz in both cases. TheNLTL principle of operationwas also studiedusingalowvoltagelinebuiltwithvaryingcapacitancediodes(varactors)inthefrequencyrange of 200‐400MHz as these components show higher nonlinearity than commercialceramic capacitors. For the gyromagnetic lines, the focus was on computer simulationsusingacircuitsimulatorcalledLT‐Spicetoeasethedesignofsuchlinesforhighfrequencyoperationabove1GHzratherthanusingcomplexnumericalcodes.Finally,theimplicationsoftheseresearchresultsondesignofNLTLswillbediscussed.

FundamentalsofThermalConductanceatElevatedTemperatures

PamelaNorris


Program:FundamentalsofThermalConductanceatElevatedTemperatures(FA9550‐14‐1‐0395)

Solid‐solidinterfacesserveastheprimaryscatteringpointtoenergycarriersatthemicro‐and smaller‐ length scales, therefore understanding, predicting, and tuning the thermalconduction across these interfaces is of paramount importance to designing energyefficient devices. Thermal boundary conductance is particularly important at hightemperatures,aboveroomtemperatures,whicharetypicaloperatingtemperaturesofhighpower, high frequency devices. Current predictivemodels do not accurately capture themagnitude or trends of thermal boundary conductance at temperatures above roomtemperature, thus intheworkpresentedhere,weaimtoelucidatetheparameterswhichinfluencethermalboundaryconductanceathightemperaturesusingcoupledexperimentalandcomputationalinvestigations.Moleculardynamics(MD)resultsshowthatforanidealinterface anharmonicity results in enhancement of thermal boundary conductance.Occurrence of anharmonic phonon events within the bulk however, can play a moreimportant role in thermal interfacial transport rather than those happening at theinterface. Time domain thermoreflectance was then used to measure the temperaturedependentthermalboundaryconductanceataseriesofinterfaces,chosensothatvaryinglevels of anharmonicity would be expected. TDTR results indicate that the effects ofanharmonicity on thermal boundary conductance, at these interfaces, can beovershadowed by the effects of interfacial features, such as roughness, diffusion, anddisorder.

ScatteringandRelaxationMechanismsDuringHighEnergyPhoto‐ExcitationofElectronicMaterials

PatrickE.Hopkins


Program:ScatteringandRelaxationMechanismsofElectronicMaterials(FA9550‐15‐1‐0079

In applications involvinghigh energy andpowerdensities, the scattering, relaxation andtransport mechanisms will be strongly coupled to the degree of carrier nonequilibriuminduced fromthedelivered fields.Thishas tremendous impactonmaterialsandsystemsused in directed energy, nonequilibriumplasma, and pulsed power applications. In thisprogram, we are studying the role of strongly perturbed electronic distributions on theheat transfer mechanisms in solid and at material interfaces. We use pump‐probespectroscopy with sub‐picosecond pulses to measure the electronic relaxationmechanisms, resultingscatteringrates,andsubsequentdiffusive thermal transportwhile

varyingthepumppulsecharacteristicstostronglyinfluencetheexcitednumberdensityinthemetalornon‐metalofinterest.Inthistalk,Iwilldiscussourstudiesontheroleofnon‐equilibriumdistributionsonelectronrelaxationinbothgoldfilmsandGaAswafers.InAufilms, we show that electron‐electron scattering along with electron‐phonon scatteringhavetobeconsideredsimultaneouslytocorrectlypredictthetransientnatureofelectronrelaxation during and after short‐pulsed heating of metals at elevated electrontemperatures. However, the role of electrons in a non‐equilibrium do not significantlycoupleenergydirectlytothephonons,indicatingthattheprimarymechanismofelectron‐phononheattransferismainlyfromthethermalizedelectronicdistribution. InGaAs,wedemonstrate the ability tomeasure the excited carrier scattering rates decay separatelyfromtheaccumulatedchargeddensity–thatis,weshowthattherelaxationratesofexcitedelectronscanbeseparatedintotworegimesbasedonthesingle‐carrier/transientresponseandtheaccumulated‐carrier/frequencyresponse.

InnovativeStudyofElectricalContactandElectronTransport

Y.Y.Lau,PengZhang


Program:InnovativeStudyofElectricalContactandElectronTransport(FA9550‐14‐1‐0309)

We systematically evaluate the current crowding and spreading resistance in thin filmcontactswithverylargecontrastsindimensionsandresistivity[1],basedonourexactfieldsolution. The current transfer length is compared with the classical transmission linemodel.Wedevelopaself‐consistentmodel for thetunnelingcurrent inaquantumdiode,includingtheeffectsofanodeemission,spacecharge,andexchange‐correlationpotential.Thisyieldsthegeneralcurrent‐voltagecharacteristicsinananoscalejunctionwhichgovernallfourregimes[2]:directtunneling,fieldemission,andbothquantumandclassicalspace‐charge‐limited regime. Also presented is our recent theory on laser induced electronemissionfromametalsurfaceunderdcbias.

WestudyvariousmechanismstoenhancethecoherentSmith‐Purcellradiation, includingoptimized grating, prebunched beams, and open cavity [3]. We examine the absoluteinstabilityatthebandedgesoftraveling‐waveamplifiers[4],andquantifythesurprisinglyhighharmoniccontentsinthesmallsignalregime[5].

[1]P.Zhang,Y.Y.Lau,andR.M.Gilgenbach,J.Phys.D:Appl.Phys.,inthepress,(2015).[2]P.Zhang,Sci.Rep.5,9826(2015).[3]P.Zhang,L.K.Ang,andA.Gover,Phys.Rev.Spec.Top.‐Accel.Beams18,020702(2015).

[4]D.M.H.Hung, I.M. Rittersdorf, P. Zhang,D. Chernin, Y. Y. Lau, T.M. Antonsen, J.W.Luginsland,D.H.Simon,andR.M.Gilgenbach,Phys.Rev.Lett.115,124801(2015).[5]C.F.Dong,P.Zhang,D.Chernin,Y.Y.Lau,B.Hoff,D.H.Simon,P.Wong,G.Greening,R.M.Gilgenbach,IEEETrans.ElectronDevices,underreview,(2015).

AdditionalAbstracts*

* (programs not presented at this review, but which are part of the Plasma andElectroenergetic Physics Portfolio; all categories; programmatic affiliations or sub‐thrustslistedwithprograminformation)

MeasurementsofOutputfromanOvermodedBWOBasedonaSurfacePeriodicLattice

AlanPhelps

DepartmentofPhysicsUniversityofStrathclyde,Glasgow,Scotland,UK

Program:HighPowerMicrowaveLow‐ContrastSurfaceArtificialMaterials(FA8655‐13‐1‐2132)‐Corefundedprogram,associations:HPEMSources&2012MURIonTransformationalElectromagnetics

Numericalfinite‐difference‐time‐domainandparticle‐in‐cellsimulationscarriedoutduringthe first years of the project have demonstrated a successful electron‐beam/waveinteraction in an overmoded, mode selective cavity formed by a cylindrical two‐dimensional periodic surface lattice. Optimization of this structure’s physical propertiesresulting in the design of a suitable cavity was reported in the Plasma andElectroenergetics program review in December 2014. During 2015 following theconstructionandcoldtestingofthecavity,electronbeamandmagneticfieldsystemshavebeendesignedandassembled.Theelectronbeampropertieshavebeenmeasuredandtheelectronbeamhasbeenusedtoexcitethecavity.Initialmeasurementshavebeenmadeofthe microwave output from the overmoded BWO, created using the two dimensionalsurface periodic lattice cavity. These initial measurements are compared with thetheoretical and numerical modelling predictions. The positive indications are that theprincipleofusingtwodimensionalperiodicsurfacelatticesallowseffectivemodeselectionin overmoded cavities, providing a route to higher output powers at higher frequencies.Futureworkwill includemoredetailedmeasurementsof themicrowaveoutput toprovetheconceptworksaspredicted.Toachieve thegreatestbenefit fromthisconceptand toachieve the greatest increase inmicrowavepower at higher frequencies thediameter towavelengthratioshouldbeincreased.

Anewfutureprojectisproposedinwhichtwodimensional,periodicsurfacelatticeswithlarger diameter to wavelength ratios will be investigated using theoretical analysis,numericalmodellingand laboratoryexperiment toexplorewhether thisprinciple canbeextended to higher diameter to wavelength ratios. This would significantly increase thehighpowercapabilityofhighfrequencymicrowavesources.

StudyofthePropagationofElectromagneticWavesinaComplexPlasma

OsamuIshihara

YokohamaNationalUniversity,Yokohama/ChubuUniversity,Kasugai,Japan

Program: Study of Complex Plasmas with Magnetic Dipoles (FA2386‐14‐1‐4021) ‐ Corefunded program, associations: International (AOARD), Fundamental Processes andInteractionsinPlasmas

Complexplasmaischaracterizedbyasystemofaplasmainwhichconductiveordielectricdustparticlesarepresent (O. Ishihara,ComplexPlasma:Dusts inPlasma, J.ofPhysicsD:Appl.Phys.40,R121(2007)).Thecomplexplasmaisrichinnovelfeaturesmanifesteditselfthroughtheinteractionofcollectionofchargeddustparticlesandthecollectivebehaviorofthebackgroundplasma.Wehavestudiedelectromagneticwavepropagationinacomplexplasmawithgaseousplasmaincludingmetallicparticles.Whenametallicparticleisplacedinanoscillatingelectric field, thepolarizationinducedinthespherestartsoscillation.Ontheotherhand,thebackgroundplasmasupportsvariouskindsofoscillations,whileonthesurface of metallic particles electrons oscillate with frequency much higher than thebackground plasma frequency. The surface plasma oscillations are known as surfaceplasmons.TheeffectivepermittivityofthecomplexplasmaisapproximatedbytheMaxwellGarnettformulation.Ourpreliminarytheoreticalstudyrevealsthepresenceofresonancesnear the surface plasmon frequency in the dielectric response function of the complexplasma, which necessarily affects the refraction nature of electromagnetic wavespropagatinginthebackgroundplasma.Asimulationofelectromagneticwavepropagationinacomplexplasmawithmetallicparticles isalsounderway.Thestudyiscarriedoutincollaboration with Sergey Vladimirov of University of Sydney of Australia and TetsuoKamimuraofMeijoUniversityofJapan.

QuantumMany‐BodyLocalizationinaStronglyCoupledUltracoldPlasma

MarkusSchluz‐Weiling1,HosseinSadeghi2,EdwardGrant1,2

1DepartmentofPhysics&Astronomy,UniversityofBritishColumbia,Vancouver,BCV6T1Z1,CANADA

2DepartmentofChemistry,UniversityofBritishColumbia,Vancouver,BCV6T1Z1,CANADA

Program: Quantum and Classical Measures of Molecular Ultracold Plasma Dynamics(FA9550‐12‐1‐0239) ‐ Core funded/BRI program, associations: Ultracold Plasma BasicResearchInitiative(BRI),FundamentalProcessesandInteractionsinPlasmas

Amany‐bodysystemofquantumparticlesquenchedonadisorderedpotentialcanundergoatransitiontoalocalized,non‐ergodicphasewiththepropertiesofaquantumglass[1{5].Well‐isolatedensemblesofultracoldatomshaveprovidedanimportantprovinggroundforsuchphenomena[6,7].Rydbergatomsinparticularoffertheadvantageofhighlytuneable,very long range interactions [8, 9].Herewepresent experimental evidence suggesting anovelroutetoastateofmany‐bodylocalizationbeginningfromaquantum‐selectedinitialstate in aRydberggasofnitricoxide. Laser‐crossedmolecular‐beamexcitation formsanellipsoidal excitation volume. Prompt Penning ionization releases electrons in the densecore of this Rydberg gas. The resulting electron‐impact avalanche forms a plasma thatspontaneouslybifurcatesandcoolsbydisposingelectronthermalenergytothemomentumofseparating,stronglycoupledultracoldplasmavolumes.Thisdisposalofenergytomasstransport quenches theplasma, relaxing the electronson adisordered ionpotential thatremainsstationaryonthetimescaleofelectronmotion.Thesecoolingdynamicsgiverisetoan extremely robust ensemble of Rydberg and quasi‐Rydberg molecules, which seemsspatially and energetically immobilized in a band of states very near the ionizationcontinuum.Undernatural,delocalizedconditions,classicalsimulationscall forthishighlyexcited ensemble of molecular ions and electrons to decay by well‐defined, readilyaccessible channels of recombination, relaxation and fragmentation to form neutraldissociation products and a hot, expanding electron gas. Instead,we observe free‐flying,localizedultracoldplasmavolumeswithprojectedlifetimesofmilliseconds,perhapstensofmilliseconds.

This work was supported by the US Air Force Office of Scientific Research (Grant No.FA9550‐12‐1‐0239).

[1] Basko, D. M., Aleiner, I. L. & Altshuler, B. L. Metal{insulator transition in a weaklyinteracting many‐electron system with localized single‐particle states. Annals of Physics321,1126{1205(2006).[2]Oganesyan,V.&Huse,D.A. Localizationof interacting fermionsathigh temperature.PhysRevB75,155111(2007).[3] Huse, D. A., Nandkishore, R. & Oganesyan, V. Phenomenology of fully many‐body‐localizedsystems.PhysRevB90,174202(2014).[4] Laumann, C. R., Pal, A. & Scardicchio, A. Many‐body mobility edge in a mean‐fieldquantumspinglass.PhysRevLett113,200405(2014).[5]Nandkishore,R.&Huse,D.A.Many‐BodyLocalizationandThermalizationinQuantumStatisticalMechanics.AnnuRevCondensMatterPhys6,15{38(2015).

[6]Kondov,S.S.,McGehee,W.R.,Xu,W.&DeMarco,B.Disorder‐InducedLocalizationinaStronglyCorrelatedAtomicHubbardGas.PhysRevLett114,083002(2015).[7]Schreiber,M.etal.Observationofmany‐bodylocalizationof interactingfermions inaquasi‐randomopticallattice.Science349,842{845(2015).[8] Schauβ, P. et al. Observation of spatially ordered structures in a two‐dimensionalRydberggas.Nature491,87{91(2012).[9] Lesanovsky, I. & Garrahan, J. P. Out‐of‐equilibrium structures in strongly interactingRydberggaseswithdissipation.PhysRevA90,011603(2014).Emission,EmittanceandEntropyofHighIntensityElectronBeams

JoelL.Lebowitz

DepartmentofMathematicsRutgers,TheStateUniversityofNewJersey,Piscataway,NJ08854‐8019

Program: Emission, Emittance and Entropy of High Intensity Electron Beams (PendingAward)‐Corefundedprogram,associations:HPEMSources

Weareinvestigatinghowtheemittedcurrentfromvarioustypesofcathodesisaffectedbyanalternatingelectricfield,e.g.E(t)=E[1+bsinwt)].Whenwissmalltheprocesscanbeconsideredquasi‐stationary.ItistheneasytocomputeitseffectonthetunnelingcurrentintheFNregime:forb=1/2thereisanenhancementbyafactorof5forarectangularbarrierandby5/2foratriangularone.

Whentheperiodoftheoscillatingfieldisclosetothetransittimeoftheelectronsfromthecathodetotheanodetheremaybesharpjumpsinthecurrentreachingtheanode.

Forlargewthesituationismorecomplicated.Theeffectnowdependsontheinteractionofthelaserfieldwiththeelectronsintheemitter.Therearevariousapproximatetheoriesintheliteratureonthisandwearetryingtosortoutwhich,ifany,areapplicabletothetypeofexperimentsdonebyDonShiffler'sgroup.Weplantostudytheconnectionbetweentheentropyofabeamanditsemittancefromthepointofviewofkinetictheoryandnon‐equilibriumstatisticalmechanics.Ourcurrentstateofunderstandingofsuchaconnection, ifany, isverypartial.Abettermicroscopic theorywillhopefullyleadtobettercontrolofbeamspreading.

TheFowler‐Nordheim theoryneedsdrasticmodificationwhen the fieldsareverystrong.AsshownbyRokhlenkosometimeagoemissionactuallydecreaseswhenthefieldbecomesverystrong.While itmaynotbepossibletousesuchsteadystatestrongfields,theeffectmayalreadyshowupevenatrealizablefields,especiallyinpulses.

abstracts computational theoretical plasma physics

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