x-ray free electron lasers - princeton plasma physics ...x-ray free electron lasers j.s. wurtele ucb...
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X-Ray Free Electron LasersJ.S. WurteleUCB and LBNL
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Light
Davidson SymposiumPPPL
June 12, 2007
X-RayFELs
Two Livingston Plots
Particleaccelerators Light Sources
PanofskyEU FEL
X-Ray FELsGoals:
• High average flux• High peak power• Temporal coherence• Spatial coherence• Attosecond pulses• Synchronization• Flexibility
• Implications (current technology):Large machines, GeV Energies
• Critical Physics• Optical manipulation of phase
space• High brightness beam generation
and preservation• Wiggler technology
Evolution of synchrotron radiation sources
X-ray sources expand
LCLS [SLAC] FEL
JAPAN [SPRING 8]
!
~8GWPeak X-RayPower
~120Hz Repetitionrate
~13.6GeVEnergy
~3.5kACurrent
EU XFEL [DESY]
Vision for a future LBNL light source
ALSFEL array at the Bevatron site
Injector
Linac in tunnel
Vision for a future light source facility at LBNLVision for a future light source facility at LBNL A HIGH REP-RATE, SEEDED, VUV — SOFT X-RAY FEL ARRAY
Low-emittance,
high rep-rateelectron gun
Array of configurable FELsIndependent control of wavelength, pulseduration, polarizationConfigured with an optical manipulationtechnique; seeded, attosecond, ESASE
Laser systems,timing &
synchronization
Beammanipulation
andconditioning
Beam distribution andindividual beamline tuning
~2 GeV CW superconducting linac
FEL BASICS
Spread in this term is harmful!
Limits
What drives X-ray FELs towards largeenergy electron beams?
1. Coherent emission--bunching at X-ray wavelengths
2. Limits on our ability to create and propagate high brightness electron beams
3. Limits on our ability to build short wavelength wigglers
z
undulator
zz
Dephasing from transverse motion
• allows relaxed emittance requirement in FEL--but we do not know how to produce requiredconditioning in a practical system (yet)
ΔE/E
with conditioning
!
+"J#
!
d"
dz=
!
J"
!
J"
!
J"
We are limited by our inability to make high quality beams
SASE FEL: amplification of fluctuations
Single pass synchrotron radiation spectrum (Catravas, et al, @BNL/ATF,)
SASE spectrum and temporal shape has spikes--poor longitudinal coherence
Seeded FEL ENHANCED CAPABILITIES FOR CONTROL OF X-RAY PULSE
Electron beam is 1.5 GeV, energy spread 100 keV, 250 A current, 0.25 micron emittance; laser seed is 100 kW at 32 nm; undulator period 1 cm
SASE
25 fs seed
500 fs seed
0.4
0.3
0.2
0.1
0.0
Photo
ns/
meV
(X1
09)
12421241124012391238
Photon Energy (eV)
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
Photo
ns/
meV
(X1
09)
12421241124012391238
Photon Energy (eV)
30
25
20
15
10
5
0
Photo
ns/
meV
(X1
09)
12421241124012391238
Photon Energy (eV)
Spectrum
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Pow
er
(GW
)
-700 -600 -500 -400 -300 -200 -100
Time (fs)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Pow
er
(GW
)
-700 -600 -500 -400 -300 -200 -100
Time (fs)
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Pow
er
(GW
)
-700 -600 -500 -400 -300 -200 -100
Time (fs)
Pulse profile
Seeded FEL close to
transform limit Nomonochromator
Phase space manipulationManipulate beam phase space can have many advantages:
Enhanced gain
Seeding radiation pulse for harmonic cascades
Attosecond pulses
Synchronization
Relax beam quality constraints (conditioning)
Lower energy for given wavelength
Many of these ideas are realized by laser interactions withthe electron beam prior to the radiation generation. Someexamples…
slice ~ 1 fs
e-beam ~ 100 fs
Lasers manipulate longitudinal phase spaceduring interaction in wiggler
This cartoon is realized by manipulation of beam phase space with shortpulse lasers. The idea is to condition and select specific slices ofelectrons to radiate differently (in direction, frequency, intensity, etc.). Forsynchrotron sources this has already been accomplished: Zholents &Zoloterev (1996); Schoenlein, et al, 2000; Khan, Part. Acc. Conf. 2005. For FEL see Zholents et al(2003-2007)
Harmonic cascade seed
Laser pulse ~ 5 fs
)t(E
Dispersive section introducesbunching
High Gain Harmonic Generation (HGHG) –seed with a laser pulse and radiate at a harmonic
L.-H. Yu et al, Science 289 932-934 (2000)L.-H. Yu et al, Phys. Rev. Let. Vol 91, No. 7, (2003)
dispersivechicane
phase
Input Outpute- beam phase space:
Laser modulates e-beamenergy
Ener
gy
!
"#
!
"Bunched beam radiates strongly atharmonic in a downstream undulator
!
n"
!
"n#
ModulatorShort wiggler
laser pulse
e- bunch
!
0"
RadiatorLonger wiggler
!
0" n
Extends energy reach, lower power
Seed laser pulseTbunch >> TMO
PMO >> Pshot
FEL modulatorLW < LSAT
Strong bunching
3rd - 5thharmonicradiator
3 - 5th harmonicFEL modulator /low gain amplifier
LW < LSAT
3rd - 5thharmonicradiator
Cascaded harmonic generation scheme
Delay bunch in micro-orbit-bump (~50 mm)
Low e electron pulse Unperturbed electronssE ~ sE (0)
seed laser pulse
tail head
radiator radiatormodulatormodulator
disrupted region
HHG laser seed--an alternative to harmoniccascades
Example with seed at 30 nm, radiating in the water windowFirst stage amplifies low-power seed with “optical klystron”
More initial bunching than could be practically achieved with a single modulatorOutput at 3.8 nm (8th harmonic)
300 MW output at 3.8nm (8th harmonic) from
a25 fs FWHM seed
1 GeV beam500 A
1.2 micron emittance75 keV energy spread
Gullans et al. (2007)
Modulator30 nm, L=1.8 m
Modulator30 nm, L=1.8 m
Radiator3.8 nm, L=12 m
100 kWl =30 nm
CourtesyH. Kapteyn
Or, X-ray laser seed
GunBeam manipulation
FELs
linac
FEL performance is governed by beam brightness:
Brightness = # electrons/6D-phase space volumeThis number will NOT get larger---
determined by gun physics and emittance or energy spread can grow through various instabilities
RCD circa ‘89
Gullans et al, 2007
Many people within LBNLMany people within LBNL contribute tocontribute to new light sourcenew light source
Walter BarryDan BatesKen BaptisteAli BelkacemJohn ByrdChris CelataChris Coleman-SmithJohn CorlettStefano DeSantisLarry DoolittleRoger FalconeBill FawleyGraham FlemingMiguel FurmanTom GallantMike GreavesSteve GourlayMichael GullensGang HuangZahid Hussein
Preston JordanJerry KekosJanos KirzJim KrupnickSlawomir KwiatkowskiSteve LeoneDerun LiSteve LidiaSteve MarksBill McCurdyPat OddoneHoward PadmoreEmanuele PedersoliGregg PennDave PlateIlya PogorelovJi QiangAlex RattiIna ReichelDavid Robin
Kem RobinsonGlenna RogersRob RyneFernando SannibaleBob SchoenleinAndy SesslerKiran SonnadJohn StaplesChristoph SteierJean-Luc VayMarco VenturiniWill WaldronWeishi WanRussell WellsRussell WilcoxJonathan WurteleSasha ZholentsMike ZismanMax Zolotorev