PAC2001 J. Rossbach, DESY 1 New Developments on Free Electron Lasers Based on Self-amplified Spontaneous Emission J. Rossbach, DESY Why SASE FELs? How

J. Rossbach, DESY1PAC2001

New Developments on Free Electron LasersBased on Self-amplified Spontaneous Emission

J. Rossbach, DESY

Why SASE FELs?

How does it work?

What are the challenges?

Where are we?

Where do we want to go?


Why SASE FELs?

State of the art:Structure of biological macromolecule

Needs 1015 samples

Crystallized not in life environment

reconstructed from diffractionpattern of protein crystal:

LYSOZYME , MW=19,806The crystal lattice imposes restrictions on molecular motion

Images courtesy Janos Hajdu


Why SASE FELs?

SINGLE MACROMOLECULE,Planar section, simulated image

courtesy Janos Hajdu

Resol. does not depend on sample quality

Needs very high radiation power @ 1Å

Can see dynamics if pulse length < 100 fs


We need a radiation source with

• · very high peak and average power• · wavelengths down to atomic scale λ ~ 1Å• · spacially coherent• · monochromatic• · fast tunability in wavelength & timing• · sub-picosecond pulse length

Why SASE FELs?

For wavelengths below ~150 nm: SASE FELs.


How does it work?

Q = Ne·e, Ne = # electrons

Point charge radiates coherently P Ne2 !

Radiation power of oscillating point-like charge Q:

P Q2 2

„Point“ means above all: bunch length < radiation

Synchrotron radiation of an incoherent electron distribution: P Ne

Potential gain in power Ne = 109 – 1010 !!


How does it work?

Coherent motion is all we need !!


How does it work?

Idea: Start with an electron bunch much longer than the desired wavelength and find a mechanism that cuts the beam into equally spaced pieces automatically

Free-Electron Laser (Motz 1950, Phillips ~1960, Madey 1970) Special version: starting from noise (no input needed)

Single pass saturation ( no mirrors needed)

Self-Amplified Spontaneous Emission (SASE)(Kondratenko, Saldin 1980)(Bonifacio, Pellegrini 1984)


How does it work?

laserbeam

undulator electronabsorber

radi

atio

n po

wer o

nlo

garith

mic

scale

lower magnetic poles of the undulator

elektromagnetic wave

electron trajectory

N

S

S

N

S

N

N

S

undulator period U

em

direction of motion

direction of motion

bunch of electronswith increasingdensity modulation

upper

of the undulator

perpendicular tomagnetic field

magnetic poles

Spectrum of amplifiedspontaneous radiation

21

2

2

2

Kuem

Resonance wavelength:


How does it work?

0.05 mm

0.0

5 m

m

Micro-bunching of the X-ray FEL electron beam

FIREFLY microbunching; Ricci,Smith/Stanford


How does it work?

105 by FEL gain

103 by improved beam quality,long undulators


What are the challenges? Overview

Electron beam parameters needed for Self-Amplified-Spontaneous Emission (SASE)

Energy:

für em= 1 Å: E 20 GeV

Energy width:

Narrow resonance E/E ≤ 10-4

Small distortion by wakefields

super conducting linac ideal!

Gain Length:3/1

2

23

0ˆ

2

3

1

IKe

mcL ur

g

21

2

2

2

Kuem

Beam size:

r 40 m high electron desity for

maximum interaction with radiation fieldEmittance ≤ need special electron source to accelerate the beam before it explodes due to Coulomb forces

Peak current inside bunch:Î > 1 kA feasible only at ultrarelativistic energies, otherwise ruins emittance bunch compressor

Straight trajectory in undulator:ultimately < 10 m over 100 m


Why a linear accelerator?

X-ray SASE FEL needs:

energy width σE/E ≤ 10-4

and bunch length σl 25 m (~100 fs)

σE σl 60 eV m

storage ring is limited to >1000 eV melectron emittance ≤ 10-11 m

LEP (20GeV) (!): x > 10-10 m

several kA peak currentwakefields tolerable for single pass, BUT not in storage ring


What are the challenges? RF gun

TESLA FEL photoinjector for small and short electron bunches


What are the challenges? Injector

Layout of integrated injector/compressor for TTF2 and TESLA FEL


What are the challenges? Bunch compression

Section

Bending Magnet Quadrupole Triplett

5 m

Instrumentation

Section

Bending Magnet Quadrupole Triplett

Tail particle, more momentumHead particle, less momentum

magnetische Strahlkompression

Rossbach/DESY

Beware of coherent synchrotron radiation (CSR)Magnetic bunch compression

very powerful microwave radiationwith >~ bunch length if bunch length << size of vacuum chamber

radiation from tail goes straight and can catch up with head of bunch

--> severe beam distortion

Beam dynamics simulation must take into account combined space charge and e.m. radiation in near-field. see: TRAFIC4 by A. Kabel/SLAC



rf0

0

2 2

2 sin coss

z y yd s

E

eV

rf0

0

2 2

2 sin coss

z y yd s

E

eV

yy--zz streak streak generated by generated by deflectordeflector

P. Krejcik et. al., P. Krejcik et. al., WPAH116WPAH116P. Krejcik et. al., P. Krejcik et. al., WPAH116WPAH116

P. Emma,P. Emma,J. Frisch,J. Frisch,P. Krejcik,P. Krejcik,G. Loew,G. Loew,X.-J. WangX.-J. Wang

f f = 2856 MHz= 2856 MHzVV00 15 MV 15 MVzz 22 22 mm

f f = 2856 MHz= 2856 MHzVV00 15 MV 15 MVzz 22 22 mm

ee

zz

2.44 m2.44 m

cc pp

90°90°

VV((tt))xx

RFRF‘‘streak’streak’

SS-band-band

Structures built at Structures built at SLACSLAC in in 1960’s 1960’s now installed in now installed in linac for testinglinac for testing

‘‘slice’-slice’- and ‘slice’ energy spread measurements also possible and ‘slice’ energy spread measurements also possible



Interferometry of coherent synchrotron radiation

Projection from longitudinal phase space tomography

Longitudinal electron bunch profile at the TESLA Test Facility measured with two different methods



Bunch compression down to few 20-30 m is a technical requirement (and complication) to achieve kA peak current for sufficiently small gain length.

It is a lucky coincidence, that the ultra-short pulse length is exactly what users are calling for. From the user point of view, bunch length should be even 10 m !

try harder!


What are the challenges? Wakefields

Wakefields from surface roughness:Test at TTF FEL

Smooth surface

Rough surface, same diameter

E

E

See Markus Hüning, Wed. afternoon


Where are we? Beam parameters

TTF FEL now TESLA FEL

(LCLS similar)

Normalized emittance from gun (Q = 1 nC) 3.5 mrad mm 0.8 mrad mm

Norm. emittance at undulator entrance 8 mrad mm 1.6 mrad mm

Beam size in undulator 100 m 40 m

Bunch length (rms) 1 ps 0.1 ps

Peak current 500 A 5000 A

Long. emittance σE σl 100 eV m 60 eV m

In all key beam parameters, the extrapolation from proven technology is a factor 2 – 10We know what to do and howWe will take further steps at TTF getting even closer to TESLA FEL parameters


Where are we? Progress with SASE FELs: VISA

see:Tremain,MurokhWPPH118/122Wed. afternoon


Where are we? Progress with SASE FELs: LEUTL


Where are we? Progress with SASE FELs: LEUTL

530 nm Energy vs. Distance along the Undulator

Exponential Growth Region

Saturation of SASE

Flash of UV light (385 nm) near saturation. The expected wavelength as a function of angle (radial offset) is clearly seen. The darker “lines” are from shadows of secondary emission monitors in the vacuum chamber.

Stephen Milton/ANLTuesday 13:30h


Where are we? Progress with SASE FELs: TESLA

Phase 1 of the SASE FEL at the TESLA Test Facility at DESY, Hamburg.The total length is 100 m.



TTF FEL undulator



SASEgain>1000

Spontaeous Emission x100

TTF FEL gainat 108 nm vs. bunch charge

By now observedgain >105





FEL wavelengths reached at TTF FEL


Where are we? Progress with SASE FELs: Summary

where wavelength year Livermore ~1 mm 1986LURE/Orsay 5-10 m 1997UCLA/LANL 12 m 1998LEUTL/Argonne 530 nm 1999

385 nm & saturation 2000TTF FEL/DESY 80-180 nm 2000VISA/BNL/LLNL/SLAC/UCLA 845 nm saturation 2001

(+2nd+3rd Harmon.)All observations agree with theoretical expectations/computer models


Where do we want to go?

SASE FEL projects under progress: min. wavelength

APS/LEUTL Phase2 120 nmAPS/LEUTL Phase3 51 nmDESY: TTF FEL Phase2 6 nm 2003/2004SPring8: ~ 5 nm - 2005

SASE FEL projects proposed:

SLAC: LCLS 0.15 nm 2006DESY: TESLA XFEL 0.085 nm 2010


Where do we want to go? Brilliance

Peak brilliance Average brilliance

LCLSmultibunch

LEUTL

TTF FEL


Where do we want to go? LCLS


Where do we want to go? LCLS

SLAC linac tunnel undulator hall

Linac-0L6 m

Linac-1L9 mrf 38°

Linac-2L330 mrf 43°

Linac-3L550 mrf 10°

BC-1L6 m

R56 36 mm

BC-2L24 m

R56 22 mm DL-2L66 mR56 = 0

DL-1L12 mR56 0

undulatorL120 m

7 MeVz 0.83 mm 0.2 %

150 MeVz 0.83 mm 0.10 %

250 MeVz 0.19 mm 1.8 %

4.54 GeVz 0.022 mm 0.76 %

14.35 GeVz 0.022 mm 0.02 %

...existing linac

new

RFgun

25-1a30-8c

21-1b21-1d

21-3b24-6dX

Linac-XL0.6 mrf=

Producing short bunches for LCLS


28 GeV28 GeV

Existing bends compress to Existing bends compress to <100 fsec<100 fsec

~1 Å~1 Å

Add 12-meter chicane compressor Add 12-meter chicane compressor in linac at 1/3-point (9 GeV)in linac at 1/3-point (9 GeV)

Add 12-meter chicane compressor Add 12-meter chicane compressor in linac at 1/3-point (9 GeV)in linac at 1/3-point (9 GeV)

Damping Ring Damping Ring (( 30 30 m)m)

9 ps9 ps 0.4 ps0.4 ps<100 fs<100 fs

50 ps50 ps

SLAC LinacSLAC Linac

1 GeV1 GeV 20-50 GeV20-50 GeV

FFTBFFTBRTL RTL

30 kA30 kA

80 fsec FWHM80 fsec FWHM

1.5%1.5%

Short Bunch Generation in the SLAC LinacShort Bunch Generation in the SLAC Linac

Compress to 80 fsec in 3 stagesCompress to 80 fsec in 3 stages

P. Emma et. al., P. Emma et. al., FPAH165P. Emma et. al., P. Emma et. al., FPAH165

New proposal for:New proposal for: LCLSLCLS accelerator optics R&D accelerator optics R&D Ultra-short Ultra-short xx-ray science -ray science

program at program at SLACSLAC


Where do we want to go? TESLA

TESLA scheme



Beam switchyard distributing the electron bunch trains to various undulators





A potential site for TESLA near Hamburg


Conclusion

SASE FELs clearly demonstrated for wavelengths far below the visible.

Full agreement with theory

User facilities in the VUV/soft X-ray range just around the corner

User facilities in the Angstrøm range are feasible with only moderate extrapolation of present state-of-the-art;Computer simulations and mechanical design are available

Accelerator physics & technology will play major role

Fun guaranteed!

Documents

PAC2001 J. Rossbach, DESY 1 New Developments on Free Electron Lasers Based on Self-amplified Spontaneous Emission J. Rossbach, DESY Why SASE FELs? How