Download - Future x-ray Free-electron laser sources
X-Ray Free Electron LasersJ.S. WurteleUCB and LBNL
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Davidson SymposiumPPPL
June 12, 2007
X-RayFELs
Two Livingston Plots
Particle accelerators Light Sources
PanofskyEU FEL
X-Ray FELs
Goals:
• 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]
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Current ~3.5kA
Energy ~13.6GeV
Repetition rate
~120Hz
Peak X-Ray Power
~8GW
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-rate electron gun
Array of configurable FELsIndependent control of wavelength, pulse duration, polarizationConfigured with an optical manipulation technique; seeded, attosecond, ESASE
Laser systems, timing &
synchronization
Beam manipulation
and conditioning
Beam distribution and individual beamline tuning
~2 GeV CW superconducting linac
FEL BASICS
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Spread in this term is harmful!
Limits
What drives X-ray FELs towards large energy 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 required conditioning in a practical system (yet)
ΔE/E
with conditioning
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+κJ⊥
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dψ
dz=
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2kwγ − γ rγ r
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J⊥
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J⊥
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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
Photons/meV (X10
9 )
12421241124012391238
Photon Energy (eV)
0.14
0.12
0.10
0.08
0.06
0.04
0.02
0.00
Photons/meV (X10
9 )
12421241124012391238
Photon Energy (eV)
30
25
20
15
10
5
0
Photons/meV (X10
9)
12421241124012391238
Photon Energy (eV)
Spectrum
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Power (GW)
-700 -600 -500 -400 -300 -200 -100
Time (fs)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
Power (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
Power (GW)
-700 -600 -500 -400 -300 -200 -100
Time (fs)
Pulse profile
Seeded FEL close to
transform limit No monochromator
Phase space manipulation
Manipulate 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 with the electron beam prior to the radiation generation. Some examples…
slice ~ 1 fs
e-beam ~ 100 fs
Lasers manipulate longitudinal phase space
during interaction in wiggler
This cartoon is realized by manipulation of beam phase space with short pulse lasers. The idea is to condition and select specific slices of electrons to radiate differently (in direction, frequency, intensity, etc.). For synchrotron 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 introduces bunching
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)
dispersive chicane
phase
Input Output
e- beam phase space:
Laser modulates e-beam energy
Energ
y
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−π
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πBunched beam radiates strongly
at harmonic in a downstream undulator
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nπ
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−nπ
ModulatorShort wiggler
laser pulse
e- bunch
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0λ
RadiatorLonger wiggler
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0λ n
Extends energy reach, lower power
Seed laser pulse
Tbunch >> TMO
PMO >> Pshot
FEL modulatorLW < LSAT
Strong bunching
3rd - 5th
harmonic radiator
3 - 5th harmonic FEL modulator /
low gain amplifierLW < LSAT
3rd - 5th
harmonic radiator
Cascaded harmonic generation scheme
Delay bunch in micro-orbit-bump (~50 m)
Low electron pulse
Unperturbed electronsE ~ E (0)
seed laser pulse
tail head
radiator radiatormodulatormodulator
disrupted region
HHG laser seed--an alternative to harmonic cascades
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 3.8 nm (8th harmonic) from
a 25 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 kW=30 nm
Courtesy H. Kapteyn
Or, X-ray laser seed
GunBeam
manipulation
FELs
linac
FEL performance is governed by beam brightness:
Brightness = # electrons/6D-phase space volume
This number will NOT get larger---determined bygun physics and can grow through various instabilities
RCD circa ‘89
Gullans et al, 2007
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Conventional Linac
Ez : 10 - 200 MV/ m
Lint : km's
Δ
~K l y s t r o n M i c r o w a v e
P o w e r S o u r c e
W a v e - g u i d e
s t r u c t u r e
Δ
~
• E • •
h ′ω
W = e Ez Lint
0 1 02 0
3 04 0
5 06 0
la s e r p u ls e
Electron beam surfing on plasma electric field
( B. Shadwick, UCB/ CBP)
Laser dr iven plasma based linac
Ez : 1 0 - 1 0 0 GV/ m
Lint : laser dif fract ion lengt h
Plasma-based Electron Linac
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
Average Brightness [Ph/(s 0.1% BW mm
2
mrad
2)]
10-5
10-4
10-3
10-2
10-1
100
101
102
103
X-Ray Pulse Duration [ps]
2nd Generation Storage Rings
3rd Generation Storage Rings
Cornell ERL (6 keV)
European XFEL (12 keV)
Seeded FEL, 750 fs (1.2 keV)
LCLS (8 keV)
BESSY FEL (1 keV)
FLASH (200 eV)
Seeded FEL, 50 fs (1.2 keV)
Seeded FEL, 100 as (1.2 keV)
Performance comparison PARAMETER SPACE COMPLEMENTS OTHER FACILITIES
Many people within LBNL contribute to new light sourceMany people within LBNL contribute to new 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
Extras
800 nm
spectral broadening and
pulse compression
e-beam
harmonic-cascade FEL
one period wiggler tuned for FEL
interaction at 800 nm
2 nm light from FEL
2 nm modulator chicane-buncher
1 nm radiator
dump
endstation
1 nm coherent radiation
e-beam
endstation
time delay chicane
Potential for attosecond x-ray production
e-beam
Zholentz and Fawley PRL 2004
X-rays from plasma sources
Already demonstrated—beams make x-rays More elaborate ideas based on ion channels [Whittum;
E157SLAC]
Rousse et al, PRL 04
Many groups worldwide are working on thisPlasma yield naturally short pulses, but hard to reachFEL intensities with spontaneous emission [N vs N^2]
The Advanced Photoinjector Experiment
– APEX*)
*) J. Staples, F. Sannibale, S. Virostek, CBP Tech Note-366, October 2006
BeamDump
Coaxial Gun Cavity
Current Monitors
Solenoid &Trim CoilPackages
LaserPort
Beam Position Monitor
Retractable Cerenkov Monitor
Pepper Pot &Faraday Cup
RetractableCerenkov Monitor
& Faraday Cup
Cathode Mounted on Coaxial Center
Conductor
Frequency 65 MHzField 12-25 MV/mRF power at 20MV/m 70 kWPeak wall power density 8 W/cm2Vacuum 10-11 Torr200 MHz is also under consideration
High repetition rate RF photocathode gun