Design of a tabletop atto-second coherent X-ray source · XFEL: Proposed future coherent X-ray source in Europe ... Apply solid-state laser and optics technology on particle acceleration

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


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




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





undulator





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


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


Cerenkov cell lens

IFEL

ITR

Cerenkov cell

Motor 1

Motor 2

upstream

downstream

Laser beam

electron beame-beam

steppermotor

steppermotor

Au coatedKapton

laser beam




z

boundary

α zα

E dzz−∞∫ >0

0 E dzz−∞

∞

∫ = 0






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





φcos∝U

Laser Polarization Angle (degrees)


Ave

rage

Ene

rgy

Mod

ulat

ion

⟨M⟩(

keV

)φcos∝U

Laser Polarization Angle (degrees)


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


channel

electron beam

cylindrical lens

top view

λ/2

λ

xyz

laserbeam


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




undulator






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

Documents

Design of a tabletop atto-second coherent X-ray source · XFEL: Proposed future coherent X-ray source in Europe ... Apply solid-state laser and optics technology on particle acceleration