basic energy sciences advisory committee meetinglcls february 26, 2001 j. hastings brookhaven...

February 26, 2001 J. Hastings Brookhaven National Laboratory

Basic Energy Sciences Advisory Committee Meeting LCLS

LCLS Scientific ProgramX-Ray Laser Physics: Advanced R&D

J. B. Hastings Brookhaven National LaboratoryFebruary 26, 2001

• Focusing of X-Ray Pulses• Generation Shorter X-Ray Pulses• Increase of Longitudinal Coherence



Working Group Members

• J. B. Hastings, Brookhaven National Laboratory, Upton, NY, USA• J. Arthur, Stanford Linear Accelerator Center, Stanford, CA, USA• P. Emma, Stanford Linear Accelerator Center, Stanford, CA, USA• A. Freund, European Synchrotron Radiation Facility, Grenoble, France• D. Mills, Argonne National Laboratory, Argonne, IL, USA• C. Pellegrini, University of California, Los Angeles, CA, USA• D. Peter Siddons, Brookhaven National Laboratory, Upton, NY, USA• R. Tatchyn, Stanford Linear Accelerator Center, Stanford, CA, USA• A. Toor, Lawrence Livermore National Laboratory, Livermore, CA, USA• L.-H. Yu, Brookhaven National Laboratory, Upton, NY, USA



•Ph

oton

s/pu

lse/

100

nm sp

ot

40%

30%

20%

15%

Relec

1010

1011

1012

1013

1014

1 10 100 1000

b Relectronic

Tolerable damage(single exposures)

Initial LCLSparameters

20% 30% 40%

Landscape of damage toleranceIonisation and subsequent sample explosion cause diffraction intensities to change

Agreement factor:

Time (fs)

I(t) - Io Io

R =Crystallographic R-factor for proteins in the PDB



Calculated limits of resolution with Relectronic = 15 %

Pulse duration (FWHM) 10 fs 50 fs 100 fs 230 fsPhotons/pulse (100 nm spot)(R = 15%)

5x1012 8x1011 3x1011 5x1010

Relative scattering power 0.71 0.96 0.97 0.99Single lysozyme moleculeMW: 19,806

26 Å>30 Å

30 Å>30 Å

>30 Å>30 Å

>30 Å>30 Å

2x2x2 cluster of lysozymes 4.8 Å16 Å

12 Å30 Å

17 Å>30 Å

25 Å>30 Å

3x3x3 cluster of lysozymes <2.0 Å3.0 Å

3.0 Å12 Å

6.5 Å17 Å

12 Å>30 Å

5x5x5 cluster of lysozymes <2.0 Å<2.0 Å

<2.0 Å2.9 Å

<2.0 Å3.9 Å

2.5 Å5.0 Å

Single RUB ISCO moleculeMW: 562,000

2.6 Å20 Å

4.0 Å25 Å

20 Å>30 Å

30 Å>30 Å

Single viral capsid (TBSV)MW: ~3,000,000

<2.0 Å2.5 Å

<2.0 Å4.7 Å

<2.0 Å22 Å

2.4 Å30 Å

Limit with 1 photon/pixelLimit with 9 photons/pixel



Temporal and Spatial Scales

Time in femtoseconds, distance in Å

H2OOH + H

CH2I2CH2I + I



Shortest Fundamental FEL Radiation Wavelength 1.5 ÅElectron Beam Energy 14.3 GeVNormalized RMS Slice Emittance 1.2 mm-mradPeak Current 3.4 kAFEL Mode Source Size (FWHM) 78 mFEL Mode Source Divergence (FWHM) 1 radPeak Brightness * 12 1032

X-Ray Pulse Length (FWHM) 230 fsAverage Time Between Micro-Pulses 0.9 fsAverage Full width of Micro-Pulses 0.2 fsAverage Number of Micro-Pulses in Pulse 250Transverse Coherence FullSlice Bandwidth 5 10-4

Projected Bandwidth 2 10-3

* photons/sec/mm2/mrad2/0.1%-BW

LCLS Baseline Design Parameters



Focusing of LCLS Pulses

• Focusing is singularly important phase space transformation of the LCLS pulse

• Available Field Strengths ~1010 V/m 1016 V/m

• Proposed R&D in six areas critical to Reflective, Diffractive and Refractive focusing

Beam Diameter ~100 m -> ~100 nm

X-ray field 5x1017 W/cm2 exceeds atomic unit: 3.5x1016 W/cm2



SLAC linac tunnelSLAC linac tunnel FFTB tunnelFFTB tunnel

Linac-0 Linac-1 Linac-2 Linac-3

BC-1 BC-2 DL-2DL-1

undulatorL120 m

7 MeVz 0.84 mm

150 MeVz 0.84 mm

250 MeVz 0.20 mm

4.54 GeVz 0.024 mm

14.35 GeVz 0.024 mm

...existing linac

(8/29/00)(8/29/00)

new

RFgun

Linac-X

Short-Pulse Generation (Electron Bunch):LCLS Accelerator and Compressor Schematic

Courtesy of P. Emma, SLAC

X



Short-Pulse Generation (Electron Bunch): Magnetic Electron Bunch Compression

z

z

z

RF AcceleratingRF AcceleratingVoltageVoltage

Path Length-EnergyPath Length-EnergyDependent BeamlineDependent Beamline

V = V0sin()

z0

z

z = R56

Under-Under-compressioncompression

Over-Over-compressioncompression

Courtesy of P. Emma, SLAC



nominal nominal LCLS LCLS compressioncompressionQQ = 1 nC = 1 nC

chirped chirped compressioncompressionQQ = 0.6 nC = 0.6 nC

230 fs230 fs

240 fs240 fs

1%1%

0.01%0.01%

E/

E

E/E

E/

E

E/E

Cur

rent

Cur

rent

Z (m) Z (m)

Z (m) Z (m)



Short-Pulse Generation (X-Ray Pulse):Based on ChirpingChirped X-Ray Pulse Generated from Chirped

Electron Pulse inFEL Undulator• 1% Chirp Amplitudes Obtainable

Optical techniques using the chirped pulseOptical Pulse CompressionOptical Pulse Slicing with Zone Plates, Multi-Layers, Crystals



Optical Compression and Pulse Slicing

Z (t)

Pulse SlicingPulse Slicing

Pulse CompressionPulse Compression



Optical Pulse Compression

Optical pulse compression by energy chirping the photon beam and compressing it with 2 gratings. Example of minimum pulse length: Minimum pulse length: ~ 10 fs Wavelength spread: 2 % Grating line separations: 5.5 m Gratings vert. separation: 75 cm Gratings hor. separation: 107 m Incident angle at grating: 0.2 mrad Grating length: 1 m

Courtesy of C. Pellegrini, SLAC

No Practical Solution No Practical Solution has yet been worked out has yet been worked out



Optical Pulse Slicing with Crystals

Minimum sliced bunch length ~ 10 fs



SASE FEL theory well developedand verified by simulations

• FEL radiation starts from noise in spontaneous radiation

• Transverse radiation electric field modulates the energy and bunches the electrons within an optical wavelength

• Exponential build-up of radiation

along undulator length

SASE FELs

Undulator Regime

Exponential Gain Regime

Saturation

0.2 fs

0.9 fs

1 % of X-Ray Pulse

Electron BunchMicro-Bunching



Longitudinal coherence

SASE FEL starts up from noise No longitudinal coherence

SeedingImpose microbunching of the electron beamOutput is the amplified inputPreserves the longitudinal coherence of the seed

An example: self seeding



Increase of Longitudinal Coherence : Two Stage FEL

Undulator 1Linac Undulator 2

Monochromator

Electrons

Electron Beam Dump

X-Rays

LCLS Spectral Properties Control



Summary

• The LCLS design opens the possibility for adjusting X-Ray beam parameters according to the needs of the experiments.

• Improvement are with high user interest include– Increased Electrical Field Strength (Focusing)

– Shorter Bunch Length (Electron Bunch / X-Ray Pulse Compression,slicing)

– Increased Longitudinal Coherence (Seeding / Monochromatization)

• All areas need extensive R&D Efforts

230 fs -> 50-20 fs

1010 V/m -> 1016 V/m

Coherence Length: 1 fs -> >100 fs

Beam Diameter: ~100 m ->below 100nm

E/E: 10-3 -> 10-6

basic energy sciences advisory committee meetinglcls february 26, 2001 j. hastings brookhaven...

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