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Design of a tabletop Design of a tabletop attoatto--second second coherent Xcoherent X--ray sourceray source
T. Plettner, R.L. ByerStanford University
FRISNO 9, Les Houches, France, 2/12-2/16 2007
Conventional coherent XConventional coherent X--ray ray facilitiesfacilities
undulator
3 km
120 m
accelerator
Experiment lines
LCLSinjector
• km-size facility• microwave accelerator• λRF ~ 10 cm• MW electr. power• 4-14 GeV e-beam
• 120 m undulator• 23 cm period• 15-1.5 A radiation• 0.8-8 keV photons• 1014 photons/sec• ~77 fsec
• separate user lines• 120 Hz pulse train
LCLS propertiesLCLS properties
TTF: Tesla Test Facility; fsec EUV SASE FEL facilityXFEL: Proposed future coherent X-ray source in Europe…TTF: Tesla Test Facility; fsec EUV SASE FEL facilityXFEL: Proposed future coherent X-ray source in Europe…
Our dreamOur dream
xyz
laserbeam
cylindrical lensvacuum
channel
electron beam
cylindrical lens
top view
λ/2
λ
xyz
laserbeam
cylindrical lensvacuum
channel
electron beam
cylindrical lens
top view
λ/2
λ
top view
λ/2
λ
• solid-state laser technology• MEMs nanofabrication technology
Apply laser-accelerator technology to miniaturize accelerators and FELs
example of an accelerator microstructure
Laser-driven electron injector
Laser-driven particle accelerator
Laser-driven dielectric undulator
The envisioned XThe envisioned X--ray sourceray source
~ 1 m
x-rays
Solid state lasersSolid state lasers
λ ~ 1 μm
• < kW of electrical power• no radiation or electrical hazards• MHz to GHz repetition rates
The envisioned XThe envisioned X--ray sourceray sourceElectron pulse structure of a linear particle accelerator
m 1~IR μλ
attosec 10~bτ
EMλ
bτ
cm 1~RFλ
psec 1~bτ
RF acceleratorlaser
accelerator
Our researchOur research
RF photocathodeelectron injector
RF - microwave metal structure
particle acceleratorPermanent magnet
undulator
Laser-driven electron injector
Laser-driven particle accelerator
Laser-driven dielectric undulator
Apply solid-state laser and optics technology on particle acceleration
Conventional electron injectorConventional electron injector
The klystron• ~2 m tall• 1/3 MV• high power• water cooling• X-ray radiation• 10 Hz rep. rate
Conventional electron injector
Temporary solution
RF cathode
LaserLaser--driven injectordriven injectorP. Hommelhoff et al, Kasevich group
Laser
field emitter tip
Field emission tip properties
1. laser-assisted tunneling of the electrons from the atom to free space
2. Highly nonlinear3. Potential for sub-optical cycle
electron emission
metal vacuum
e
Laser
field emitter tip
Electrostatic lens
GND
Accelerator cell
grid
MCP
10 fsec
LowLow--energy laserenergy laser--particle acceleratorparticle accelerator
1. multiple-electron emission2. focusing with electrostatic lens3. verify ultra-low emittance4. verify ~700 attosec bunch5. modulate energy
objectives
Our researchOur research
RF photocathodeelectron injector
RF - microwave metal structure
particle acceleratorPermanent magnet
undulator
Laser-driven electron injector
Laser-driven particle accelerator
Laser-driven dielectric undulator
Apply solid-state laser and optics technology on particle acceleration
Idea of laserIdea of laser--driven particle driven particle accelerationacceleration
First publications date back to 1970
W.D. Kymura et al, Phys. Rev. Lett. 74, 546–549 (1995)J. A. Edighoffer et al, Phys. Rev. A 23, 1848 (1981).
I. Wernick and T. C. Marshall, Phys. Rev. A 46, 3566 (1992).
W.D. Kymura et al, Phys. Rev. ST AB 4, 101301 (2001)
Inverse FEL accelerators (IFEL)Inverse Cerenkov accelerators (ICA)
gradient ||E∝
2.2 atm. H2
gradient ⊥∝ Evacuum
DielectricDielectric--structure based structure based vacuum laser acceleratorsvacuum laser accelerators
Vacuum channel
Dielectric structure
Laser in
Main concept ||Eq
cβ
Synchronous accelerating force in the vacuum channel
DielectricDielectric--structure based structure based vacuum laser deflectorsvacuum laser deflectors
Vacuum channel
Dielectric structure
Laser in
Main concept ⊥Eq
cβ
Synchronous deflection force in the
vacuum channel
ProofProof--ofof--principle experimentprinciple experiment
electronbeam
materialboundary
θ
Ez
8 μm Kapton1 μm Au
laserbeam
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Visible-laser acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. Lett. 95, 134801 (2005)
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Proof-of-principle experiment for laser-driven acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. ST Accel. Beams 8, 121301 (2005)
FWH
M e
nerg
y sp
read
(keV
)
laser timing (psec)
FWH
M e
nerg
y sp
read
(keV
)
laser timing (psec)
laser on
laser off
gradient ||E∝Linear Linear accelerationacceleration synchronicity
vacuum
ProofProof--ofof--principle experimentprinciple experiment
laser off
laser on
-3 -2 -1 0 1 2 3-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
optical phase
elec
tron
ener
gy (
a.u.
)
A
D
electronbeam
Proof-of-principle setup• single laser-electron interaction• crossed laser beams• vacuum space• dielectric cell
laser beam
Relativistic electrons30 MeV
energy spectrometer
ProofProof--ofof--principle experimentprinciple experiment
Cerenkov cell lens
IFEL
ITR
Cerenkov cell
Motor 1
Motor 2
upstream
downstream
Laser beam
electron beame-beam
steppermotor
steppermotor
Au coatedKapton
laser beam
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Visible-laser acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. Lett. 95, 134801 (2005)
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Proof-of-principle experiment for laser-driven acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. ST Accel. Beams 8, 121301 (2005)
ProofProof--ofof--principle experimentprinciple experiment
z
boundary
α zα
E dzz−∞∫ >0
0 E dzz−∞
∞
∫ = 0
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Visible-laser acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. Lett. 95, 134801 (2005)
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Proof-of-principle experiment for laser-driven acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. ST Accel. Beams 8, 121301 (2005)
ProofProof--ofof--principle experimentprinciple experiment
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Visible-laser acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. Lett. 95, 134801 (2005)
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Proof-of-principle experiment for laser-driven acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. ST Accel. Beams 8, 121301 (2005)
laserEU ∝
Peak Longitudinal Electric Field Ez (MV/m)
0.1 0.2 0.3 0.4Laser Pulse Energy (mJ/pulse)
0.05
Ave
rage
Ene
rgy
Mod
ulat
ion
⟨M⟩(
keV
)
( ) ( )25.035.0017.0349.0 ±−⋅±= zEM
Average FWHM energy broadening
laserEU ∝
Peak Longitudinal Electric Field Ez (MV/m)
0.1 0.2 0.3 0.4Laser Pulse Energy (mJ/pulse)
0.05
Ave
rage
Ene
rgy
Mod
ulat
ion
⟨M⟩(
keV
)
( ) ( )25.035.0017.0349.0 ±−⋅±= zEM
Average FWHM energy broadening
ProofProof--ofof--principle experimentprinciple experiment
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Visible-laser acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. Lett. 95, 134801 (2005)
T. Plettner, R.L. Byer, E. Colby, B. Cowan, C.M.S. Sears, J. E. Spencer, R.H. Siemann, “Proof-of-principle experiment for laser-driven acceleration of relativistic electrons in a semi-infinite vacuum”, Phys. Rev. ST Accel. Beams 8, 121301 (2005)
φcos∝U
Laser Polarization Angle (degrees)
Average FWHM energy broadening
Ave
rage
Ene
rgy
Mod
ulat
ion
⟨M⟩(
keV
)φcos∝U
Laser Polarization Angle (degrees)
Average FWHM energy broadening
Ave
rage
Ene
rgy
Mod
ulat
ion
⟨M⟩(
keV
)
Many possible architecturesMany possible architectures
Hollow core PBG fibers 3-D photonic bandgap structures
B. M. Cowan, Phys. Rev. ST Accel. Beams , 6, 101301 (2003).X.E. Lin, Phys. Rev. ST Accel. Beams 4, 051301 (2001)
Y.C. Huang, et al, Appl. Phys. Lett. 68 (6) (1996) 753.
laser beams
l1 l2
xyz
laserbeam
cylindrical lensvacuum
channel
electron beam
cylindrical lens
top view
λ/2
λ
xyz
laserbeam
cylindrical lensvacuum
channel
electron beam
cylindrical lens
top view
λ/2
λ
top view
λ/2
λ
Semi-open structures Periodic phase modulation structures
T. Plettner et al, Phys. Rev. ST Accel. Beams 4, 051301 (2006)
Grating based geometryGrating based geometry
λ vacuum channel
λperiodic boundary
periodic boundary
absorbing boundary
scatter region
E yiHz
i
E y
Hz
Ex
source waveE y
iHzi
Grating based geometryGrating based geometry
5λ
Finite timeFinite time--domain field calculationdomain field calculation
Grating based geometryGrating based geometryFinite timeFinite time--domain field calculationdomain field calculation
||E⊥E
ADD A
( ) ( )∫ ⊥⊥ ×+=λ
λ 0
1 dzzBvEG
( )∫=λ
λ 0||||
1 dzzEG
Avg. acceleration
Avg. deflection
accel.phase
defl.phase
A:
D:
0
max ||
=⊥G
G
0
max
|| =
⊥
G
G
Grating based geometryGrating based geometryE-beam lithography + DRIE
1 cm long interactionGradient ~ 0.7 GeV/menergy gain: 7 MeV
Aperture ~ ½ λGradient ~ 2.5 GeV/mStructure impedance ~ 40 Ω
10 fsec,λ = 1μm
200 fsec,λ = 800 nm
Electron temporal pulse Electron temporal pulse structurestructure
cm 1~RFλ
psec 1~bτ
m 1~IR μλ
attosec 10~bτ
RF accelerator
laser accelerator
Optical bunchingOptical bunching
optical buncher
opticalaccelerator
compressor chicane
laser
IFEL
(compressor)
laser accelerator
-8 -6 -4 -2 0 2 4 60
20
40
60
80
100
120
140
160
P has e
His togram In P has e
Analytic (1-D)S imulation
0 1 2 3 4 5 6-40
-30
-20
-10
0
10
20
30
40
Phase
Mea
n En
ergy
Shi
ft (k
eV)
Net Acceleration
Fit Amp=17 keV
mea
n en
ergy
shi
ft (
keV
)
phase
Net acceleration
mea
n en
ergy
shi
ft (
keV
)
phase
Net accelerationExpected bunching Expected energy gain
• IFEL modulates energy spread• electron drift creates optical bunches• second accelerator net acceleration
Experiment features
RF photocathodeelectron injector
RF - microwave metal structure
particle acceleratorPermanent magnet
undulator
Laser-driven electron injector
Laser-driven particle accelerator
Laser-driven dielectric undulator
Apply solid-state laser and optics technology on particle acceleration
Our researchOur research
electron bunch travels slower than photons
FreeFree--electron radiationelectron radiation
Lu > 10 m
SASE FEL X-ray
sub psec
Concept of an Concept of an undulatorundulatorelectron bunch
(sub-psec)
permanent magnets λu > 1 cm T 1≤B
22~
γλλ u
center wavelength
Free-electron laser amplification
local micro-bunching
coherent radiation
FEL equationsFEL equationsEvolution of the transverse optical field due to the electron’s Evolution of the transverse optical field due to the electron’s motionmotion
⎥⎦⎤
⎢⎣⎡
∂∂
+∂
∂−=
⎥⎥⎦
⎤
⎢⎢⎣
⎡∇−⎟
⎠⎞
⎜⎝⎛
∂∂
+⎟⎠⎞
⎜⎝⎛
∂∂
⊥ xc
tJ
cE
ztcex
xρ
ε2
20
222 11
( ) ⎟⎟⎠
⎞⎜⎜⎝
⎛−=′
∂∂
ΔΔ∈
−∑ vetzEt j
i jψχ2,~γε
βχ0
2 2Kqc
=R. Bonifacio, C. Pellegrini, L.M. Narducci, “Collective Instabilities and high-gain regime in a free electron laser”, Opt. Comm. 50, 373-378 (1984)
Slow envelope approximationSpeed-of-light frame
growth rate of the field γ
λ 313132eu nB
∝
Steady state growth solution
Conventional Conventional undulatorsundulatorsTTF TTF UndulatorUndulator at DESYat DESYPermanent magnets
T ~ mm, 27~ 21Buλ
Electron beam
Gain lengthm 6.0~GL
Undulator lengthm 27~UL
~ ½ GeV
km 41
FEL wavelength(VUV) nm 30~Rλ
TESLA Test Facility FEL
Phase II
~1 GeV, ~1mmicro-
undulator < 1m
?
Permanent magnet Permanent magnet undulatorundulator
growth rate of the field γ
λ 313132eu nB
∝
Limited by the beam emittanceRF accelerator: ε ~ 10-6 m-radLaser accelerator ε ~ 10-10 m-rad
Compact 1m accelerator 1-2 GeV maximum
X-rays
T 21=B
~200 μm
~50 μm
~ 40 cm
~200 μm
~50 μm
~ 40 cm
mm ~ 21
uλ
?~uL
~Rλ 0.2 Å
~1 GeV, ~1m
injector laser acceleratorundulator
High strength Nd:Femicromagnets
FELFEL--growth numerical modelgrowth numerical model
( ) ⎟⎟⎠
⎞⎜⎜⎝
⎛−=′
∂∂
ΔΔ∈
−∑ vetzEt j
i jψχ2,~
ηψuk
dtd 2=
ψχη sin01Edtd
−=
Electron pendulum equationsElectron pendulum equations
Optical field growthOptical field growth
FEL physics model computer models
• Analytical 1-D, steady state× No space charge× No slippage× No velocity spread× No diffraction
• 1-D, time dependentslippageenergy spreadtemporal structure
× no lateral velocity× no diffraction
• 3-D, time dependentlateral velocity (emittance)space chargediffraction
Electron space chargeElectron space charge
( ) ( ) ernrF e=⋅∇ sp
GENESISGENESIS
GENESISGENESIS• FORTRAN based code• runs in batch mode• developed at DESY by Swen Reiche• designed to handle nC charges macro-particles• can turn space charge on and off
• include focusing elements into the modelinclude focusing elements into the model•• widely tested (TTF, LCLS, Brookhaven,widely tested (TTF, LCLS, Brookhaven,……))
properties
Guess •Spot size•focusing
GENESISLsat
scan•spot size•focusing
optimum•spot size•focusing
spot size
focusingelements
Permanent magnet Permanent magnet undulatorundulator
0 0.5 1 1.5 2 2.50
0.01
0.02
0.03
0.04
0.05
0.06
0.07
position in the undulator (m)
peak
pow
er (T
W)
1.8 m
~200 μm
~50 μm
~ 40 cm
~200 μm
~50 μm
~ 40 cm
m 2~uL
Electron beam
Energy: 2 GeVEnergy spread: 0.5%Spot size: 89 nmEmittance: 10-10 m-radBunch charge: 1 pCBunch length: 10 attosec
Undulator
FODO lattice 50 periodsFocusing 19 T/mm
LaserLaser--driven driven undulatorundulator
Laser plane wave
0 0.5 1 1.5 2 2.50
0.2
0.4
0.6
0.8
1
1.2
1.4
position in the undulator (m)
peak
pow
er (T
W)
permanent magnet
undulator
laser-driven
undulator
GeV/m 1~⊥G
T 3~0B
cm 10~SATL
~ 10 cm
LaserLaser--driven driven undulatorundulator
0 5 10 15 20 250
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
time (attosec)
pow
er (T
W)
~ 5 attosec
~1 GeV, ~1m
~Rλ 0.2 Å
injector laser accelerator undulator
~ 10 cm
0 0.05 0.1 0.15 0.20
2
4
6
8
10
12
14x 10
11
position in undulator (m)
optic
al p
ower
(W)
space charge on
space charge off
X-ray pulse
FEL amplitude growth X-ray output pulse
LaserLaser--driven deflector driven deflector experimentexperiment
screen
First near-term future experiment
SummarySummary1. Structure loaded vacuum laser acceleration
• Similar to RF, but λ ~ 1μm solid-state lasers• Possibility for attosecond electron bunches• Proof-of principle demonstration• Staged acceleration optical bunches• Future near-term MEMS structures• Utilization of attosec electron bunches
for light sources
2. Laser-driven unduator• Advantage over permanent magnet devices
• Monolythic• Stronger deflection
3. Eventual objective• tabletop all-laser injector, accelerator and
undulator
AckowledgementsAckowledgements
1. Northrop Grumman Corp.
2. E. Colby
3. R. Ischebeck