# Presentation: 099876

## LCLS Scientific ProgramX-Ray Laser Physics: Advanced R&DJ. B. Hastings Brookhaven National LaboratoryFebruary 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*

## Landscape of damage tolerance

**Photons/pulse/100 nm spot**

**Landscape of damage tolerance**

- Ionisation and subsequent sample explosion cause  diffraction intensities to change

- Agreement factor:

**Time (fs)**

- Crystallographic R-factor for proteins in the PDB

## Calculated limits of resolution with   Relectronic = 15 %

**Calculated limits of resolution with   R****electronic**** = 15 %**

**Limit with 1 photon/pixel**
**Limit with 9 photons/pixel**

## Temporal and Spatial Scales 

**Time in femtoseconds, distance in ****Å**

**H****2****O********OH + H**

**CH****2****I****2********CH****2****I**** + I**

## Shortest Fundamental FEL Radiation Wavelength	1.5	Å
Electron Beam Energy	14.3	GeV
Normalized RMS Slice Emittance 	1.2	mm-mrad
Peak Current	3.4	kA
FEL Mode Source Size (FWHM)	78	m
FEL Mode Source Divergence (FWHM)	1	rad
Peak Brightness *	12	1032
X-Ray Pulse Length (FWHM)	230	fs
Average Time Between Micro-Pulses	0.9	fs
Average Full width of  Micro-Pulses	0.2	fs
Average Number of Micro-Pulses in Pulse	250	
Transverse Coherence	Full
Slice Bandwidth	 5	10-4
Projected Bandwidth	 2	10-3
 * photons/sec/mm2/mrad2/0.1%-BW

- Shortest Fundamental FEL Radiation Wavelength	_**1.5**_	Å
- Electron Beam Energy	14.3	GeV
- Normalized RMS Slice Emittance 	1.2	mm-mrad
- Peak Current	3.4	kA
- FEL Mode Source Size (FWHM)	78	m
- FEL Mode Source Divergence (FWHM)	1	rad
- Peak Brightness *	12	1032
- X-Ray Pulse Length (FWHM)	230	fs
- Average Time Between Micro-Pulses	0.9	fs
- Average Full width of  Micro-Pulses	0.2	fs
- Average Number of Micro-Pulses in Pulse	250
- Transverse Coherence	Full
- Slice 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 ~10****10**** V/m ****10****16**** 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

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

- SLAC linac tunnel

- FFTB tunnel

**Linac-0**

**Linac-1**

**Linac-2**

**Linac-3**

**BC-1**

**BC-2**

**DL-2**

**DL-1**

- undulator
*L*120 m

- 7 MeV
***z * 0.84 mm

- 150 MeV
***z * 0.84 mm

- 250 MeV
***z * 0.20 mm

- 4.54 GeV
***z * 0.024 mm

- 14.35 GeV
***z * 0.024 mm

*...existing linac*

- (8/29/00)

- new

**RF**
**gun**

**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 Accelerating
- Voltage

- Path Length-Energy
- Dependent Beamline

*V* = *V*0sin(**)

- ***z*0

- ***z*

- *z* = *R*56**

- Under-compression

- Over-compression

**Courtesy of P. Emma, SLAC**

## nominal LCLS compression

*Q* = 1 nC

- chirped compression
*Q* = 0.6 nC

- 230 fs

- 240 fs

- 1%

- 0.01%

- E/E

- E/E

- E/E

- E/E

- Current

- Current

- Z (m)

- Z (m)

- Z (m)

- Z (m)

## Short-Pulse Generation (X-Ray Pulse):Based on Chirping

***Chirped X-Ray Pulse Generated from Chirped Electron Pulse in***
***FEL Undulator***
*1% Chirp Amplitudes Obtainable *
***Optical techniques using the chirped pulse***
*Optical Pulse Compression*
*Optical Pulse Slicing with Zone Plates,*
*      **Multi-Layers, Crystals*

## Optical Compression and Pulse Slicing

**

*Z (t)*

**

- Pulse Slicing

- Pulse 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 has yet been worked out *

**Notes:**
The 2% wavelegth spread is tota (+-)
Energy spread in electron bunch: +- 0.5 % total, rms ~0.25 %

To tune for different wavelengths, range is +- 10-20 %, for a larger range one would have to change the gratings. 

To tune in length we need to change th energy spread or the separation.
Crystals are not tunable.

## Optical Pulse Slicing with Crystals

- Minimum sliced bunch
- length ~ 10 fs

**Notes:**
Multilayer select longitudinally, selecting the range that fulfills the Braggs condition.
Bandwidth of multilayer is 0.17 %, chirp in wavelength is 4%, 0.17x230/4=10 fs. Limits is the bandwidth of the multilayer.

## SASE FELs

- and 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*
***Seeding***
*	**Impose microbunching of the electron beam*
*	**Output is the amplified input*
*	**Preserves the longitudinal coherence of the seed*
***An example:  self seeding***

## Increase of Longitudinal Coherence : Two Stage FEL

- Undulator 1

- Linac

- 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