Recent Work on
Laser and Beam – Driven Wakefield Acceleration
Chan Joshi University of California Los Angeles USA
SupportedbyUSDOE,
BIG PHYSICS GETS SMALL
UCLA Program on Plasma Based Accelerators
C. Joshi, P.I. W. Mori, Co-P.I.
C. Clayton, Co-P.I. 2005-Present
EXPERIMENTS Dr. Chris Clayton Dr. Sergei Tochitsky Ken Marsh Jay Sung, Neptune Lab, graduated Joe Ralph, Neptune Lab, graduated Fang Fang, Terawatt Lab, graduated Dan Haberberger, Neptune Lab Art Pak, Terawatt Lab Tyan-lin Wang, LLNL 2 students to be recruited for SLAC
Collaborators: Professors Musumeci, Rosenzweig & Pellegrini ( UCLA) Dr. M. Hogan (SLAC) Professors T. Katsouleas, P. Muggli ( Duke & USC ) Dr. Dustin Froula (LLNL) Professor Luis O Silva ( IST )
THEORY & SIMULATIONS
Prof. Warren Mori Chengkun Huang, graduated Wei Lu, graduated Miaomiao Zhou, graduated M.Tzoufras , graduated Weiming An
Alumni of UCLA Plasma Accelerator Group Still active in Plasma Acceleration (1985- present)
C.E..ClaytonUCLA(1983‐present)T.Katsouleas,DeanofEngineeringDukeUniversity(1984‐1989)WarrenMori,ProfessorUCLA(1982‐present)DonUmstadter,ProfessorU.Nebraska/U.Michigan(1982‐1987)WimLeemans,HeadL’OasisLabLBNL(1987‐1991)YoniyoshiKitagawa,ProfessorOsakaU/Hama’tsu(1988‐1989)RonWilliams,ProfessorFA&M(1986‐1992)PatricMuggli,ResearchProfessorUSC(1992‐1996)DanGordon,NRL(1992‐1997)CatalinFilipSpectraPhysics(1997‐2003)LuisOSilvaProfessorISTPortugal(1995‐1998)WeiLu,ResearcherUCLA(2000‐2006)ChengkunHuang,ResearcherLANL(2001‐2007)J.Ralph,ResearcherLLNL(2001‐2008)M.TzoufrasOxford(2000‐2007)
AlsoJ.M.Dawson,F.F.Chen,TTajima,P.Chen(Priorto1985)
Plasma Based Accelerators
Plasma Wake Field Accelerator A high energy electron bunch
• Laser Wake Field Accelerator A single short-pulse of photons
• Drive beam
• Trailing beam
• Wake: phase velocity = driver velocity
Vgr
T.TajimaandJ.M.DawsonPRL(1979)P.Chenet.al.PRL(1983)
Largewakeforalaseramplitudeao=eEo/mωoc ~ 1orabeamdensitynb~ no
Forτpulseoforderπωp‐1~100fs(1017/no)1/2andspot
sizec/ωp:
P~15TW(τpulse/100fs)2laser
Ion channel formed by complete evacuation of plasma electrons
Ideal linear focusing force Uniform acceleration in transverse dimension
Blowout and Bubble Formation Regime Rosenzwiegetal.1990PuhkovandMeyer‐te‐vehn2002
Nodephasing Significantdephasing
Intense Beams of Electrons for Plasma Wakefield Acceleration
N=4x1010
Energy50GeV
RepRate60HZ
Energy/pulse320JFocalSpotSize10microns
PulseWidth50fs
FocusedIntensity7x1021W/cm2
Comparabletothemostintenselaserbeamsto‐date
Onlyplaceintheworldtostudythistopic!!
Collaborators
Page 7
PWFA :
Experimental Setup
e- spectrumX-ray basedspectrometer
e- beamfrom SLAClinear accelerator
e- bunch lengthautocorrelation ofcoherent transition
radiation (CTR)
e- spectrum?erenkov light
in air gap
e- spatialdistribution
optical transitionradiation (OTR)
trapped particles
plasma
oven
notch
collimator
?erenkov
cell
spectrometer
magnet
beam
stopper
imaging?erenkovmonitor
spectro-graph
30‐40GeV
10‐100GeV
Energy Gain Scales Linearly with Length
PLASMALENGTH(cm)
0 10 20 30
BREAKING THE 1 GeV BARRIER
M.HoganetalPhysRevLeX(2005)
Nophaseslippagebetweenpargclesthemselvesandbetweenpargclesandwake
Energy Doubling of 42 Billion Volt Electrons Using an 85 cm Long Plasma Wakefield Accelerator
Nature v 445,p741 (2007)
42GeV 85GeV
Spectacular Progress in Plasma Wakefield Acceleration
RAL
LBLOsaka
UCLA
E164X
ILC
ANL
Plasma Accelerator Progress “Accelerator Moore’s Law”
E167
LBNL
WorkingMachinesDoingphysics
Max.EnergyinExperiments
E+
E-
driver
load
Generation of High Quality Beams
Themostpressinggoalisthedemonstra_onofonestageofa10‐25GeVplasmaacceleratormodulewithsmallenergyspread&emiXanceandatleast1nCcharge.
FACET : Facility for AA Research @SLAC
Beam-Plasma Accelerators: Where to next?
Laser Wakefield Accelerator Limits to Energy Gain W = eEzLacc
• Dephasing:
• Depletion: For a0 > 1 Ldph~ Ldepl
€
Ldif ≅ πLR = π 2w02 /λ
order mm! (but overcome w/ channels orrelativistic self-focusing)
cVgr
€
Ldph =λp 2
1−Vgr corder 10 cm x 1016/no
• Diffraction:
Needtoincreasetheelectron‐wakeinterac_onlength
Self Guiding Could Simplify GeV- Class LWFA
• Self-Guiding of Laser Pulses in the Blowout Regime J.Ralph et al PRL 102,175003 (2009)
• Quasi-Monoenergetic Electron Acceleration to 720 MeV using Callisto Laser at LLNL.
D.Froula et al to be published PRL (2009)
• Ionization Induced Trapping for Injecting electrons in Low Density Wakes.
• A.Pak et al PRL submitted (2009)
. Experiments for Extending the Self-Guided Regime to beyond 1 GeV. ( UCLA/LLNL collaboration : Unpublished )
Pulse evolution is minimized if this is satisfied. For W0 close to this size the pulse is predicted to reach a steady state at Wmatched
Self-Guiding in the Blow-Out Regime
1. W. Lu, C. Huang, M. Zhou, M. Tzoufras, F. S. Tsung,W. B. Mori, and T. Katsouleas, Phys. Plasmas 13, 056709(2006)
€
δnn
≥
4k pW0( )2
⇒ k pW0( ) ≥ 2GuidingCondigon:
MatchingCondigon1:
This gives a minimum density where self-guiding can occur for a given W0
02 aWkRk matchpbp ≈≈
Matchedspotsize
BlowoutCondigon:
€
ao > 2
Theaccelera_ngstructureneedstoremainasstable, for this purpose we choose the laserspotsizeandintensityfromthecondi_on:
The accelera_ng field in the ion channeldecreases linearly from the front reachingminimumvaluewithmagnitude:
Theaccelera_onprocessislimitedbydephasing:
Physical picture of Self guided LWFA
Parameter design for GeV and beyond for LWFA
P(PW) τ(fs) np(cm‐3) w0(µm) L(cm) a0 Q(nC) E(GeV)
0.100 60 2.0×1018 15 0.9 3.78 0.40 1.06
0.250 60 1.0×1018 20 1.0 3.15 0.30 2.0
WeiLuet.al.PRST‐AB07
Callisto Laser at LLNL : 300 TW Maximum Power
Current
Planned
Collaborators
• D.Froula• F.Albert• P.Michel• L.Divol• T.Doeppner• J.Palastro• J.Bonlie• D.Price
LLNL
• C.Clayton
• K.Marsh
• A.Pak• W.Lu
• J.Ralph
• S.Margns
• W.Mori
• C.Joshi
UCLA
ThisworkwasperformedundertheauspicesoftheU.S.DepartmentofEnergybyLawrenceLivermoreNagonalLaboratoryundercontractDE‐AC52‐07NA27344.
• B.Pollock• J.S.Ross
• G.Tynan
UCSD
D.Froulaetal,PhysRevLeXs,accepted(2009)
J.RalphetalPhysRevLeXs(2009)
A.Paketal,PysRevLeXs,SubmiXed(2009)
Self-Guiding in the Blow-Out Regime
J.RalphetalPhysRevLejs(2009)A.G.R.ThomasPRL(2007)
Self-Guiding in Blow-Out Regime
LaserSpotatentrance
LaserSpotatExit:NoPlasma
PICSimulagonMatchedBeamGuiding
GuidedSpotAtExit:Simulagons
GuidedSpotatMatchingCondigon
Lessthanmatched
Closetomatched
Greaterthanmatched
Foragivenaoandlaserspotsizematchingachievedbyvaryingplasmadensity
€
kpRb ≈ kpWmatch ≈ 2 a0
Transmitted Laser Spectrum at Matched Density Confirms Self-Guiding
IncidentLaser
TransmijedImagedLaserspectrum
PhotonDecceleragonPhotonAcceleragon
J.RalphetalPhysRevLejs(2009)
Pump Depletion Limited Guided Beam propagation of Ultra- short, Intense Laser Pulses
Capabili_esWavelength 806nmContrast ~105Energy >15JPulsewidth <60fsReprate 2/hour
The UCLA/LLNL collaboration : 200 TW Callisto Laser Facility at the Jupiter Laser Facility @ LLNL
20fsOscillator/PulseStretcher
Self Guided LWFA on Callisto Laser @LLNL
Upto15Jin60fs,30%incentralspotMaximumpowerontarget:80TW
HeGasjet/GasCelltargets
DualScreenSpectrometer
D.FroulaetalPhys.Rev.LeXs.SubmiXed2009
Threshold for Self- Trapping in the Self-Guided Regime Measured
TrappingThreshold
~3
SaturatedCharge
~5
40TWCoupledtoWake
Simulagons
Experiment
D.FroulaetalPhys.Rev.LeXs.Accepted2009
A self-injection density threshold is measured at 3x1018 cm-3
Themeasuredself‐injecgonthreshold(3x1018cm‐3)limitsenergygaintolessthan1GeV
• Image plates are absolutely calibrated for charge
• No electrons were self-injected and accelerated above 100 MeV at densities less than 3x1018 cm-3
P=65TW
0
0.1
1
10
100
1000
0 1 2 3 4 5 6Densityx1018(cm‐3)
Charge(p
C)
Froulaet.al.Phys.Rev.Lej.(2009)
Theenergyintheelectronbeamsweremeasuredtoincreaseastheelectrondensitywasreduced
The energy is measured to increase with decreasing density and agrees
well with analytical scaling*
No electrons were accelerated beyond 100 MeV for densities less than 3x1018 cm-3
3‐mm120MeV
5‐mm350MeV
8‐mm720MeV
Electron
Ene
rgy
Electron
Ene
rgy
Electron
Ene
rgy
0
0.5
1
1.5
2
0 2 4 6 8 10Densityx10 18(cm ‐3)
Max.Ene
rgy(GeV
)
*W.LuPRSTAB(2006)
P=75TW
3x10186x10189x1018
Density(cm‐3)
Ionization Induced Trapping in Laser-Produced Wakes
• Usetraceatomswithalargestepinionizagonpotengal
• Weuse9:1He:Nitrogenmix.• ThetwoHeelectronsandthe
first5(L‐shell)Nelectronsformthewake
• The6th(Kshell)nitrogenelectronisionizedinthewakeandtrappedmoreeasilybythewakepotengalthantheelectronsthatsupportthewake.
• Ionizagontrappingreducesthewakeamplitudeandthereforethelaserpowerneededtotrapelectrons.
E.OzetalPRL2007A.PaketalsubmijedPhysRevLej(2009)T.R.Rpwland‐ReesetalPRL(2006)
Threshold Behavior Consistent with Ionization Induced Trapping in LWFA
9:1He:N2Plasma
Nochargebelowaoof2.3inpureHeplasma A.PaketalsubmijedPhysRevLej(2009)
Tunnel Ionization of Nitrogen K-shell Electrons into LWFA
9:1He:N2Plasma
PICSimulagonsExperiment
A.PaketalsubmijedPhysRevLej(2009)
Ionization Trapping Signature in Transmitted Laser Spectrum
AddigonalBlueShin
HePlasma 9:1He:N2Plasma
IonizagonofthesixthNitrogenelectroninsidethewakeproducesaddigonalblueshin
A.PaketalsubmijedPhysRevLej(2009)
Measurement of Beam Divergence in Plane of Laser Ionization Induced Injection and Trapping
Diagnosis of the Plasma and the Wake in a 1.4 cm Long Gas Cell
Interferometry
ExitSpotSizeandImagedSpectrum
K-Shell Electrons of Oxygen Injected into Wakes
100MeV
500MeV
1000MeV
2000MeV
Energy
Uptp2.5pCofchargeabove1GeVMaximumEnergy1.7GV
10‐5
0.0001
0.001
0.01
0.1
1
0.1 1Energy(GeV)
Charge/M
eV
3x1018 1x1018 1x1018
50TW 50TW 85TW
Continuous electron spectra are measured with a 3% CO2 mixture
This collaboration has pushed the limits of energy gain in LWFA while demonstrating the limitations of self-injection
The electron energy is measured as a function of plasma length
The density is reduced to match the plasma length to the dephasing
length
TrappingThreshold3x1018cm‐3
1.5x1018cm‐3
5mm 8mm 14mm
100MeV
500MeV
1000MeV
2000MeV
Ionizagoninducedtrapping
0
500
1000
1500
2000
2500
2 4 6 8 10 12 14 16En
ergy m
ax(M
eV)
PlasmaLength(mm)
Self‐Injecgon
PlasmaLength
Energy
LLNL/UCLACollabora_on:Unpublisheddata
He He He:CO2
Two-stage simulations demonstrate monoenergetic 1.5 GeV electron beams using the Callisto laser conditions : 80 TW
OSIRIS simulations were used to design a two-stage density profile
for future Callisto experiments
Two-stage injector produces a 1.5 GeV monoenergetic electron beam
Callisto experimental parameters were used in this simulation
No self-injection occurs at these conditions; trace amounts of O2
provide injection
0 0.75 1 5
1.5x1018ccHeGas
mm
InjecgonStage1.5x1018cc
97%He+3%O2Gas
15
1.5cmAcceleragonStage
Energy(GeV)
0 0.5 1 1.5
Charge(a
rb.u
nits)
LLNL/UCLACollabora_on:Unpublisheddata
Summary on LWFA
• Amatchedlaserpulsecanbeselfguided
inaplasmaoverdistancesofinteresttoobtainelectronenergiesinthe1+GeVrange.
• Needlaserpowerontheorder100TW• Self‐trappingmaybedifficultatdensi_esontheorder1e18
cm‐3.
• Ioniza_oninducedtrappingmaybeapromisingwayofinjec_ngelectronsinlowdensitywakes.
Conclusions
BothbeamdrivenandlaserdrivenPlasmawakefieldAccelera_onconceptshavemade
remarkableprogress.
RobustGeVscaleLWFAwithingraspwith100TWlaserusingself‐guidedregime.
Expectmucheffortincontrollinginjec_on,beamloading,andemiXanceinthenextfewyears.
John M. Dawson1930-2001
“ThisisastoryofScienceasaLivingThingtakingUnexpectedturnsindirec_onsthatwereneverforeseen.Sciencemusthavegoals,butitmustAlsohavethefreedomtofollowupinteres_ngAndunexpectedresultswhentheyturnup.Thisiswhatexcitesthegoodyoungresearcheranditisintheirhandsthatourfuturerests.”
JohnDawsonAIPConf.Proc.560p3(2000)PersonalRecollecRonsontheDevelopmentofPlasmaAcceleratorsandLightSources
EPILOGUE
Par_cleSimula_onsofexperimentalcondi_onshowself‐guiding,injec_onandpeakenergy
• self‐injecgonoccursaner3mmofpropagagon
• Attheendofthe8.5mmsimulagon,aquasi‐monoenergegc760MeVelectronbeamisproduced