X-Ray Free Electron LasersJ.S. WurteleUCB and LBNL

N

S

S

NS

SN

N

e-

lw

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