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Beyond 3rd Generation: Overview

NSF Workshop on Light Source FacilitiesLawrence Livermore National Laboratory

January 9-10, 2008

S. KrinskyBNL

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Fourth Generation Sources

• Storage Ring

• Energy Recovery Linac

Continuous Sources

• Self-Amplified Spontaneous Emission

• Seeded Free-Electron Laser

Pulsed Sources

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Courtesy D. MonctonCourtesy J. Corlett

Light Source Development

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Horizontal emittance determined by equilibrium between radiation damping

and quantum fluctuation: !H~"2/MCell3

Small emittance (~30pm)! large circumference (>2km) and small dispersion ! strong chromaticity sextupoles ! Limited dynamic aperture

& energy acceptance! short lifetime & difficult injection

One possibility is to have an accumulator ring and the storage ring and transfer

the beam periodically (few minutes) via on-axis injection

Fourth Generation Storage Ring

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Energy Recovery LinacSuperconducting linac: after use the electron beam is re-circulated through

the linac at decelerating phase returning energy to the RF cavities

Emittance is determined by the normalized emittance of the electron source

! = !n / "

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Cornell Energy Recovery Linac (ERL)

Courtesy S. Gruner

Modes Hi-flux

Hi-Coherence

Energy (GeV) 5 5Current (mA) 100 25Bunch Charge (pC) 77 19Repetition Rate (MHz) 1300 1300

Geom. Emittance, both Horiz. & Vert. (pm)

30 8

RMS Bunch Length (fs) 2000 2000

Relative electron energy spread (x10-3)

0.2 0.2

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Tran

sver

se c

oher

ent f

ract

ion

Ph/s

/0.1

%/m

m2 /m

rad2

Key technical challenges

• development of low emittance, high average current electron source

• transport of the electron beam while maintaining the small emittance

• achieve level of stability now routine in storage rings

Cornell Energy Recovery Linac (ERL)

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r

)2

21(22

Kwr !"

#

$$

wr N1

"%$$

Undulator Radiation

&&&&

'

(

))))

*

+

!!" 222

2122

)( ,##

$,$ Kwr

w

w

r NK 21

2/1 2

220 "

!"

% ,#$$

w

rw L

$, "

$$$ wcoh N"%" /.2!

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….....Z=0 Z=Lw

undulatorelectrons Radiation

tj : arrival time of jth electron at z=0

- . - .je

tiN

jeEE/

// 0"

"1

~

1

~

- . - . - . - . 123

456 7!8 9

2

1 1 tieee etndtNNNII ///

Incoherent emission Coherent emission

Coherent emission is important when electrons are bunched on scale of the radiation wavelength

Coherent Emission

- .tn - .tE

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:# sin;"%

At resonance, while traversing one period of the undulator, the electron falls one radiation wavelength behind the EM-wave

swr

K $$#

"!22

2/21

Energy Modulation of Electron Beam

: =Phase of electron relative to EM-wave

##%

:

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energymodulatorseed ! dispersion section

R56Radiator out !/m

Optical Klystron

056 #

#%"% Rse-

e-

:## sin0

;"%

##%

: :

- .:n

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J

tTJ

oEtc <

=<

"=

<

<7> ?)22

212(

Energy Modulation

Spatial Bunching

=

Ee-,aw

FEL Amplifier

@A$

4w

GL 8

- .B CA

ew

II

KJJK

Area 2/12/)2( 2

223

!"

#A$$

@

@#D# E

A$

#FF

4~n"

- . - . - .GeVEAmpIGWP esat @8

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- .G

r

LzNoiseseed

av eeddP

ddP

ddP 2

2

2

91

/D//

///

77

112

3

445

6&'(

)*+!&

'(

)*+8

time

Sin

gle

shot

inte

nsity

/DA /"cohT

Sin

gle

shot

spe

ctru

m

/D

SASE

Av

Spec

trum

….....Tb Z=0 Z=Lw

undulatorelectrons SASE

SASE: Single Transverse Mode, Many Longitudinal Modes

# temporal modes=Tb/Tcoh

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100 nm 0.15 nm (LCLS) 0.1 nm(XFEL)Energy (GeV) .3 14 20

Peak Current (Amp) 500 3400 5000

N. Emittance (mm-mrad) 3 1.2 1.4

Energy Spread (%) .05 .01 .005

Undulator Length (m) 15 120 170

Pierce Parameter 2x10-3 5x10-4

Difficulty increases as output wavelength decreases

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...existing linac

L0

rfgun

L3L1 X L2

Single bunch, 1nC, 1.2#m!rad,"120"H*

Key Technical Challenges

• Photo-injector (project has achieved excellent results)

• Bunch compression and transport through maintaining

e-beam brightness

• Controlling wakefield effects

• Trajectory through long undulator

• Production of fs pulses

undulator

LCLS

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modulator radiatordispersion section

Using seed one can achieve full temporal coherence

• energy modulation

• spatial bunching in dispersion section

• coherent emission in first part of radiator

• exponential gain in second part of radiator

seed output

High-Gain Harmonic Generation (HGHG)

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Spectrum of HGHG (800nm!266nm) and unsaturated SASE under the same electron beam condition

0.23 nm FWHM

SASE x105

Wavelength (nm)

Inte

nsity

(a.u

.)

HGHG

L.H. Yu et al

BNL/

DUV-FELPRL 91 (2003)

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" 5" 25"

e- e-

Cascaded HGHGUse output of one HGHG stage as input to next

Key Technical Challenges

• Development of short wavelength seed laser

• Synchronization of lasers

• Demonstration of cascading

• Tunable output wavelength

(Shaftan & Yu have demonstrated scheme to vary output wavelength

with constant seed wavelength)

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A Seeded X-Ray FEL User Facility

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source # trans. modes

# long. modes

photons/pulse

pulses/second

ERL 1-2 104 106 109

LCLS 1 103 1012 102

XFEL 1 <103 1012 104

SXFEL 1 1 >1011 106

Based on table from D. Moncton

Performance Goals