Teravolt-per-meterplasmawakefieldsfromlow-charge,femtosecondelectronbeams

J.B.RosenzweigUCLADept.ofPhysicsandAstronomy

FACETIIScienceWorkshopOctober19,2017

BrightnessBegetsBrightness:ElectronsandPhotons

• Lightsourcerevolutionduetoe- beamimprovements

• Twoordersofmagnitudeproducequalitativelynewlightsource,theX-rayFree-electronLaser– Intensecoldbeam;instability

– 8ordersofmagnitudephotonbrightness

• Forneedede-beam,mustcompresstofsscale• Ultra-bright,Å,coherent,fseclightsource

– X-rayFEL:manyordersofmagnitudeleapforward

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Be =2Iεn

2 →2 ×1014 A/m2

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Erad ∝ exp z /Lg( ); Lg ∝ Be−1/ 3

Ultra-shortXFELpulses:motivation• Toolatatomicelectron spatio-temporalscales

– Angstroms-nanometers(~Bohrradius)– Femtoseconds (e- motion,Bohrperiod;femto-chemistry,etc.)

• 100fsaccessiblewithstandardapproaches• Promisingpath:ultra-short,lowQelectronbeam

– MyriadofadvantagesinFELand beamphysics• Mitigatecollectiveeffectsdramatically

– Robustinapplication:XFEL,coherentoptical/IRsource• Canalsousemicrobunching…• Spin-offtoultra-highfieldPWFA!

Beamphysics:fromplasmatoplasma• Beamatlowerenergyissinglecomponentrelativisticplasma

• Preserveoptimizeddynamics:changeQ,keepingplasmafrequency(n,aspectratio)same

• Dimensionsscaleas– Shorterbeam,easiertocompress– Bigemittance reduction,easytofocus– Result:ultra-highbrightnessbeam

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σ i ∝Q1/ 3

J.B. Rosenzweig and E. Colby, Advanced Accelerator Concepts p. 724 (AIP Conf. Proc. 335, 1995).

Ultra-shortpulsesatSPARX(LNF)

• Chicanebunchingaftervelocitybunching• Use~1pC beamforsinglespike

– SS:cooperationlength=bunchlength• Short,lowemittancebeamatfinalenergy2.1GeV

• Veryhighfinalbrightness– 2ordersofmagnitude!

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εnx ≅ 7.5 ×10−8 m - rad

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B = 2 ×1017 A/m2

sz =4.7 µm after velocity bunchingFinal ongitudinal phase space Final current profile

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σ t ≅ 600 attoseconds(!)

SingleSpikeX-rayFEL

• Singlespike,>1GWpeakpower• 480attosecond rmspulseat2nm• 1st timeinX-rayregime

s (µm)

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ΔωΔt = 1.67

l (nm)z (m)

z

z

Example:LCLSw/sub-fspulse• Useevenshorter0.25pCbeam,150aspulse

– Singlespikew/standardLCLSundulator

• Obtainultra-compact“LCLS” at4.3GeV• Extendenergyreachto83keV(0.15Å)

Gain evolution at 13.6 GeV; 0.15 Å, 83 kV FEL Gain evolution for 1.5 Å 4.3 GeV (0.25 pC)

Short undulator!

HighinterestinFELcommunity…low-QexplorationsatLCLS

20 pC, 135 MeV, 0.6-mm spot diameter, 400 µm rms bunch length (5 A)

OTR screen with transverse

deflector ON

0.14 µm

Emittance near calculated thermal emittance limit

Low emittances at LCLS with 20 pC. Diagnostic limited

sz » 0.6 µm

8 kA?

LiTrack(no CSR)

Photo-diode signal on OTR screen after BC2, bestcompression at L2-linac phase of -34.5 deg.

Horizontal projected emittance measured at 10 GeV LCLS FEL simulation at 1.5 Å; not single spike.

1.5 Å,3.6´1011 photonsIpk = 4.8 kAge » 0.4 µm

2fsbeamsattemporalmeasurementresolutionlimit

• Coherenttransitionradiation(destructive)• Non-destructive:coherentedgeradiation(CER)

Combined ER and SR0

0.2

0.4

0.6

0.8

1

1.2

0 50 100 150 200

Spec

tral i

nten

sity

( µJ/T

Hz)

f (THz)

QUINDI simulation FACET II case

Advancedacceleratorphysics:focusingultra-shortbeams

• 2fs(600nm)beampredictedtohaveIp=8kA• Focustosr<200nm(lowemittance enables…)• Surfacefields

• TV/m(100V/Å!)infsunipolar(1/2-cycle)pulse– Newtoolforhighfield-matterinteraction(AMO,nuclear)– FACETIlimit~100GV/m– emittance toohigh!

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eEr ≈ remec2Ip /ecσ r

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Er ≈1 TV/m!

Howtofocus?• Veryshortfocallengthfinalfocus• Useultra-highfieldpermanentmagnetquads

– mitigatechromaticaberrations– FF-DD-Ftriplet,adjustthroughquadplacement

• Developed570T/mPMQfields- Needslightlystronger,noproblem(Pr gives>1kT/m)

Small aperture PMQ B’=570 T/m Halbach PMQ as built

Final beam sizes: ~130 nm

CollectiveBeamField-inducedTunnelingIonization

¡ “Weaker” fields:tunneling¡ Regimewellunderstood

¡ ADK perturbationtheory¡ Developedforlasers¡ ADK-basedsimulation

(OOPIC,Vsim)¡ Benchmarkedtoe-beam

experiments(E167andsuccessors)

Tunneling Ionization

1TV/mReachestheBarrierSuppressionRegime(BSI)

¡ BSI:e- classicallyescapesatom¡ Previouslyonlyreached

experimentalbylasers¡ Theoryconcentratesonlasers

¡ BSInotwellunderstood¡ Non-perturbative¡ Empiricalformulas

¡ Fundamentalatomicphysicstool¡ Plasmawakefields…

BSIionizationoccursin2fscase• Extensiontounipolarfieldpulse

– approachofBauer,etal.inlasercontext

• BSIimportantabove40GV/m,buttunnelinghasalreadybeenaccomplished…

• FortotalionizationtrustOOPIC

0

0.2

0.4

0.6

0.8

1

1.2

-6 -4 -2 0 2 4 6

Normalized EIonization fraction

Frac

tiona

l Ion

izat

ion,

Nor

mal

ized

Ele

ctric

Fie

ld

t (fs)

Fractional ionization due to BSI, 800 GV/m peak, 2 fs gaussian pulse

TV/mPlasmaWakefieldAccelerator• Ultra-highbrightness,fsbeamsinplasma• Use20pCLCLSbeaminhighn plasma• In“blowout” regime:totalrarefactionofplasmae-s

– Beamdenserthanplasma– Verynonlinearplasmadynamics– Pureioncolumnfocusingfore-s– EMacceleration,independentofr– Generalmeasureofnonlinearity:

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˜ Q ≡Nbkp

3

n0

= 4πkpreNb

<< 1, linear regime> 1, nonlinear "blowout" ⎧ ⎨ ⎩

MAGIC simulation of blowout PWFA case

-1.5

-1

-0.5

0

0.5

1

1.5

0 0.5 1 1.5 2 2.5

.

F/m

Wakes in blown out region

SinglebunchexcitationatFACETII

• Beammustbeshortandnarrowcomparedtoplasmaskindepth

• Inthiscaseimplies,blowout• With2fsFACETIIbeamwechoose• For20pCbeam,wehave• Linear“Cerenkov” scaling

• 1TV/mfields,convertedEr)• Collaborationinitiated(authors)

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nb > n0

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σ r < kp−1

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σ z < kp−1

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˜ Q > 1

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n0 = 7 ×1019 cm-3

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˜ Q = 7OOPIC simulation of LCLS case

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eEz,dec ≅4e2Nb

σ z2

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eEz,dec =e2Nbn k( ) −1n k( )

dk∫ ⇒=e2Nbkp2

Beam-fieldinducedionization• Focusbeamto<200nmrms• RadialE-field>TV/m• IonizationstudiedinLi,Hgas(ADKmodel,whichappliesinbeamhead…)

Complete ionization in LiHydrogen, ionization complete inside beamOOPIC study, 3.15 atm hydrogen ionized by beam

Well-focused,denseelectronbeamcanleadtoioncollapse

• Positiveions“focused” byultra-densee-beamfields

• Nonlinearfields,emittancegrowth.Badforlinearcolliderapplications

• Detect10-100keVions(hydrogen)

Non-uniform ion density enhancement Beam mismatch and growth (e-growth)

Increasedbrightnesswithinreach

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250 MV/m peak field S-band cryogenic gun with cryostat, focusing magnets

Brightnessatphotocathode

• Brightness atcathode:• In1Dlimit,peakcurrentfromapulsedphotocathodeis

• Brightnessis

• Loweremissiontemperatureand/or…• Lesson:increaselaunchfield

21

Be =2Iεn2 =

2Jmaxmec2

kBTc

Jz,b ≈ecε0mec

2 E0 sinϕ0( )2

Be,b ≈2ecε0kBTc

E0 sinϕ0( )2

Dramaticallyhighergradientsinhigheryieldstrengthmaterials

• SLACX-bandstudiesonhardCu,CuAgalloyshowgreatimprovement

• Cryogenicstructures giveyethighergradients,and lowerdissipation

22Game changing technique for high launch fieldsPractical limit (dark current) ~300 MV/m presently

500 MV/m beforebreakdown

TopGun

GPTsimulationof200pCcase• Uselongcigar-like beam(10ps)• Emittanceen=45nm-rad

– TentimessmallerthanpreviousexampleCurrent I=20 ABrightness a recordfor this charge

Be = 2×1016 A/m2

This is six times what is available ata reoptimized LCLS

Compression is hard. Use ESASEmicrobunching

ESASEresultsat100pC• 100pC(10ps),36nmemittance• Shortperiodcryo-undulator, l=9mm,K=1.8• Operationat14GeVgives80keVX-ray• Saturationin<20m,with70GWpeak

24Current profile (10 kA) Energy evolution

Using10kApeakmicrobunchedbeaminPWFA

• Utilizequasi-nonlinear(QNL)regimeperiodicexcitation(ubunchingperiod=plasmaperiod)

• Highlyfocusedbeam(22nm),peakEr>5TV/mn0 = 2.5 ×1020 cm−3

Resonant excitation to >3 TV/m4 drive pulses + witness

Experimentalimplementation• Beamfocusing

– Few-100nmbeamdemandsmini-betaPMQs

• Plasmasection– ~3-30atm gasjet,withBSI.Startwithtenuousgas

– Length~0.5mmgives~GeV DE,“perturbative”• Beamdiagnosticsinentirelynewregime

– Longitudinal:coherentedge/transitionradiation– Transverse:

• Ionization,appearanceintensity• coherence

Sub- µmbeamtransversediagnosis

• Measuresub-µmbeamsizeswithcoherentimaging(borrowedfromXFEL).Coherentinformationdownto100nm?

Coherent transition radiation imaging reconstruction expt., A. Marinelli et al., PRL 110, 094802 (2013)

Reconstructed phase Reconstructed profile Incoherent (detuned) OTR

Conclusions• Attosecond e-beamscanbereachedatlowQ• Greatlyenhancedbeambrightness

– Singlespike,compactFELs– Newhighfieldsources,enhancewavelengthrange

• Frontierregimeforbeams;coherentopticalradiation,ionization,newdiagnostics

• Enablesnewfrontiers:– Extremeplasmawakefield accelerators

• TeV/mat1atm• Resonantlydrivenoptical/IRwavelengths(beamiseasier,better!)• Ultra-highfieldatomic-physics– TV/munipolarfield