LLNL-PRES-687440This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

Using Neutrons to Diagnose Kinetic Phenomena in Interpenetrating FlowsDrewP.Higginson,S.C.Wilks,A.Link,R.Hatarik,S.V.Weber,D.Ryutov,S.Ross,H.-S.Park(LLNL),F.Fiuza (SLAC),A.Zylstra (LANL),C.K.Li,H.Sio (MIT)

KineticPhysicsWorkshop5– 7April2016

2LLNL-PRES-687440

ACSELcollaboration(AstrophysicalCollisionless ShockExperimentswithLasers)

LLNL (USA): H.-S. Park, J. S. Ross, D. Casey, D. P. Higginson, C. Huntington, B. Remington, H. Rinderknecht,D. Ryutov, S. Weber, D. Turnbull, B. Pollack, S. Wilks

Osaka U. (Japan): Y. Sakawa, H. TakabeKyushu U (Japan): T. MoritaOxford U (UK): G. Gregori, J. Meineke, M. LevyPrinceton U (USA): A. Spitkovsky, D. Caprioli, J. ParkSLAC (USA): F. FiuzaLLE (USA): D. Froula, G. Fiskel, P.-Y. ChangU. Of Chicago: D. Lamb, P. TzeferacosRice U. (USA): E. LiangYork U (UK): N. Woosley, R. CrowstonU. Of Mich (USA): P. Drake, C. Kuranz, W. WanLULI (France): M. KoenigMIT (USA): C. Li, R. Petrasso, H. Sio, B.Lahmann, G. Sutcliffe, M. Gatu-Johnson,

W. Kabadi, L. Milanese, F. SeguinUCSD (USA): F. Beg, C. KraulandLANL (USA): A. Zylstra

3LLNL-PRES-687440

GoalistoStudyAstrophysically RelevantCollisionless Shocks

[1] Huntington et al., Nat. Physics, 11, 215 (2015)[2] Kato et al., ApJ, 681, L93, 2008

[1]

Weibel mediated density filaments

shock[2]

§ Collisionless shocksinastrophysicalphenomena(e.g.SNR)arethoughttoacceleratehighestenergy(1019 eV)cosmicrays.

§ ExperimentsatOmega:longWeibel filamentsbutnotenoughtime/density/spacetogrowintoashock.

§ ExperimentsatNIF:higherdensity,largervolume,longertimes.Canwedriveacollisionless shockatNIF?

§ Also,agreatplatformtoinvestigatekineticandmulti-fluidphenomena.

4LLNL-PRES-687440

1.E+08

1.E+09

1.E+10

1.E+11

5 6 7 8 9 10 11

Neu

tron

Yie

ld

Separation Distance [mm]

NeutronYieldRatiosSuggestaMildlyCollisionalRegime

Two types of target (CD/CD & CD/CH)Different Separations (6 – 10 mm) CD/CD

CD/CH

CD alone

§ YieldratioofCD/CD:CD/CH onNIFgivesinsightintocollisionality.

§ A)Ratioof2-4xsuggestsstagnationandshock.B)Ratioof‘infinity’(CD/CH=0)suggestsnointeraction(i.e.“collision-less”).

§ Weareinaregimeofmoderatecollisionality betweenbeam.Thuswerequirecollisional,kineticmodeling.

8x

12-16xCD CD

CD/CD CD/CH

250 kJ

CD CH

6 – 10 mm 6 – 10 mm

5LLNL-PRES-687440

PlasmaParametersSuggestFlowisSemi-collisionlessBeam-BeamandCollisionalWithinaBeam

6 mm 10 mmne 3. 1020 6. 1019 cm-3 / flownC/D/H 4. 1019 9. 1018 cm-3 / flowv 1000 1000 km/sλC-C 1.6 3.4 mmτC-C 1.6 3.4 nsTi 1 0.4 keVvth,D 220 140 km/svth,C 90 60 km/sτii 8 8 psλii 1 0.5 µm

Beam

-Bea

mIn

tra-B

eam

Plasma Flow Parameters

�bb ⇠✓A

Z

◆2 �v4

Zne

�th = vth⌧th

§ Themfp forbeam-beamcollisionsisclosetothesystemsize.Timescalesaresimilartotheobservedneutronduration(1-3ns).

§ Wecanvarythecollisionalitybychangingtheseparationofthefoilstochange(ni).

§ Withinthebeamstheionsarecollisionalwithverylowmfp.

6LLNL-PRES-687440

ModelLaserwithHydraandHandofftoPICforInterpenetration

Step 1: Single foil with 2D HYDRA

ElectronDensity

Step 2: Opposing foils with LSP

From S. Weber

250kJperfoilfor5ns,at3.5ns

Takethisflow,andsenditbackagainstitself.Symmetrizespherically.

UseLSP(PIC)tomodelinterpenetrationandhasneutronpackage.*NoEMfieldsused.

* A. Link

∆x = 20 – 100 µm∆t = 0.2 ps1600 part./species/cell

7LLNL-PRES-687440

Interpenetrationoftheflows

D H

Pz � P✓

Pz + P✓

Pz = 12mini

�v2 + v2rms

�

neutron production C C

8LLNL-PRES-687440

NeutronsProbeBeforeThermalization isCompleted

9LLNL-PRES-687440

Beam-Beam(CD/CD)NeutronsProbeEvenEarlier

10LLNL-PRES-687440

SyntheticnTOFs AgreewithDataandShowDopplerShift

Sim

Sim Norm.

Exp.

6 mm

CD CH 5o

139o 97o

CD/CH 6 mm § SimulatedNeutronsarerunpassedthroughthe(time/energy)diagnosticresponse.

§ Reasonableagreementwithwidthandshift.Thoughnotwithyield.

§ ADopplerisobservedintheforwardandbackwarddirections.

2.45 MeV+tbang

11LLNL-PRES-687440

IntheSymmetricCD/CDCaseUpshiftisObserved

6 mm

CD CD 5o

139o 97o

CD/CD 6 mm § Again,goodagreementwithexperiment.

§ Allanglesseemtobeupshiftedinenergy.

§ Thewidthsofthedistributionsvarywithanglewiththelargestwidthat90°.

2.45 MeV+ tbang

12LLNL-PRES-687440

NeutronVelocityShiftMirrorsTargetAssymetries

Sim

Exp. § Weobserveanangledependentshiftinneutronenergyintheasymmetriccase.

§ Weobserveaisotropicenergyboostinthethesymmetriccase.

§ Thedatafitscomefromshifted-Gaussianthatisdependentonthebangtime*.Errorbarsmaybeslightlyoverconservative.

SimExp.

*from R. Hatarik

13LLNL-PRES-687440

NeutronKinematics

vr = |v1|+ |v2|v1 v2

vc.m. =12 (|v1|� |v2|)

v0 = 21.65 Mm/s (2.4495 MeV)

DD

n vn

Head-on DD Reaction

vn ' v0 +0.748

v0v2r + vcm cos ✓ � 1

v0v2cm sin

2 ✓

§ Theneutronenergy(i.e.velocity)isdependenton:

1) TheQ-valueofthereaction(v0).

2) AnangularlydependentDopplershift,whichislinearlydependentoncenter-of-massvelocity.

3) Anisotopicboostofenergyfromtherelativevelocityoftheinteraction.

14LLNL-PRES-687440

DeuteronVelocityRecoveredfromNeutronEnergyShift

Sim

Exp.

1250 km/s

1000 km/s

750 km/s

750 km/s 500 km/s

250 km/s

§ FittingtheneutronshiftswiththeoreticalvaluesallowsflowvelocitytobeinferredforCD/CHandCD/CD!

§ Inferreddeuteronvelocitiesareweightedtotheneutronemissionandthusdifferwiththetarget.

CD/CD neutron Peak

CD/CH neutron Peak

v2 = 0

v2 = v1

15LLNL-PRES-687440

TheSimulationsSeemtoReproducetheNuclearData

Oursimulationsagreewith:

§ Neutrontimehistory(i.e.bangtimeandburn-width).

§ Shape(comparedwithimagesofprotonself-emission).

§ Brysk or“Apparent”iontemperatures.Seemstobeamesurement ofradialexpansion.

§ Velocityshifts

But…

16LLNL-PRES-687440

YetwestillfindaNeutronYieldDeficiency

1.E+08

1.E+09

1.E+10

1.E+11

5 6 7 8 9 10 11

Neu

tron

Yie

ld

Separation Distance [mm]

§ MatchtoCD/CDyieldisfairlygoodespeciallyattheclosestseparations.

§ CD/CHyieldisunder-predictedby3–12timesandgetsworsewithdistance.

§ Thissuggeststhatwearemissingsometypeof“scattering”astheplasmabecomeslesscollisional.

§ Thiscouldbeduetocollision-less(i.e.electro-magnetic)effectsbecomingimportant.

CD/CD

CD/CH

CD alone

Simulations

17LLNL-PRES-687440

Summary

§ Wehaveinvestigatedtheinterpenetrationofflowsandexaminedthetransitionfromfewcollisionsintostagnation.

§ Neutrondiagnosticsarefoundtobeanexcellentwindowintotheinitialstagnationwhenkineticeffectsshouldbemostimportant.Couldbeusedasadopant.

§ Shiftsintheneutronmean-energyareidentifiedasameasurementofthevelocityoftheflowthatisweightedbytheproductionprobability.

§ Thereisstillsomethingmissinginourmodelsthatmustbeincludedtoreproducethemysteriesofourexperiments.

19LLNL-PRES-687440

Shapeofneutronself-emissionissimilartoexperimentalprotonimages

Bothimagesare“pancaked”withsimilardimensionsThisisfurtherevidencethatmodelingisdoingadecentjobofcapturingtheessentialphysics.

Spatialextentoftheregionwherefusionisoccurring.

Courtesy A. Zylstra

Simulated“neutronimage”“Y”:fwhm =1.2mm

“x”:fwhm

=3.2mm

Experimental“protonimage”

CD CD

D+D® 3He + n (2.45 MeV)D+D® T + p (3.0 MeV)

20LLNL-PRES-687440

NIFexperiments

Severaldiagnosticswerefielded,butwe’llfocusonneutronTime-Of-Flight(nTOF)

Two different types of target

Target for NIF N141022 shot

5o

95o

140o

CD

CD or CH

21LLNL-PRES-687440

Whataboutthemeanenergy?

CleardependenceofneutronenergyonanglewasobservedinthesimulationsfortheCDàß CHcase.Wasthispresentinexperimentalneutrondata?

SimulationspredictedverydifferentmeanenergiesfortheCDàß CHcasethatshouldalsobepresentintheexperiment.

Neutron Energy (MeV)Neutron Energy (MeV)

CDàßCD CDàßCH

< 𝑬𝒏 >< 𝑬𝒏 >

< 𝐸& >=12𝑚& 𝑣&- + 𝑣/012𝑐𝑜𝑠𝜃

7

22LLNL-PRES-687440

Plannedexperimentswillreachthecollisionless regime

6 mm 10 mm 20 mm

Astheseparationdistanceincreases,wewillapproachacompletelycollisionless regime,andalsokeepthedensityhighenoughsothattherewillenoughc/𝜔9: ‘stoseecollisionlessshockformation.

Deuteron phase space for CD <à CD case for 3 separation distances

FutureNIFexperimentswillprobeintolesscollisionalregimes