# Presentation: 468077

## New Developments on Free Electron LasersBased 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?

- J. Rossbach,DESY

## Why SASE FELs?

**State of the art:**
- Structure of biological macromolecule

- Needs 1015 samples

- Crystallized  not in life environment

- reconstructed from diffraction
- pattern of protein crystal:

- LYSOZYME , MW=19,806

- The crystal lattice imposes
- restrictions on molecular motion

- Images courtesy Janos Hajdu

- J. Rossbach,DESY

## 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

- J. Rossbach,DESY

## 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

- ·    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.

- J. Rossbach,DESY

## 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 !!

- J. Rossbach,DESY

## How does it work?

- Coherent motion is all we need !!

- J. Rossbach,DESY

## 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)

- J. Rossbach,DESY

## How does it work?

- Spectrum of amplified
- spontaneous radiation

- Resonance wavelength:

- J. Rossbach,DESY

## How does it work?

- FIREFLY microbunching; Ricci,Smith/Stanford

- J. Rossbach,DESY

## How does it work?

- 105 by FEL gain

- 103 by improved beam quality,
- long undulators

- J. Rossbach,DESY

## What are the challenges?		Overview

- _Electron beam parameters needed for_ _S__elf-__A__mplified-__S__pontaneous __E__mission __(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:

- _Beam size:_
- r  40 m  high electron desity for maximum interaction with radiation field
- Emittance   ≤ 
- 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

- J. Rossbach,DESY

## 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 m

- electron emittance   ≤    10-11 m
- 			LEP (20GeV) (!): 	x  > 10-10 m

- several kA peak current
- 			wakefields tolerable for single pass,
- 			BUT not in storage ring

- J. Rossbach,DESY

## What are the challenges?		RF gun

**TESLA FEL photoinjector for small and short electron bunches **

** **

- J. Rossbach,DESY

## What are the challenges?		Injector

-  Layout of integrated injector/compressor for TTF2 and TESLA FEL

- J. Rossbach,DESY

## What are the challenges?		Bunch compression

- Beware of
- coherent synchrotron radiation (CSR)

- Magnetic bunch compression

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

- J. Rossbach,DESY

## What are the challenges?		Bunch compression

- P. Krejcik et. al., **WPAH116**

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

*f *= 2856 MHz
*V*0  15 MV
***z*  22 **m

*S*-band

- Structures built at ***SLAC*** in 1960’s  now installed in linac for testing

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

- J. Rossbach,DESY

## What are the challenges?		Bunch compression

- 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**

- J. Rossbach,DESY

## What are the challenges?		Bunch compression

- 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! 

- J. Rossbach,DESY

## 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

- J. Rossbach,DESY

## 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 – 10**
**We know what to do and how**
**We will take further steps at TTF getting even closer to TESLA FEL parameters**

- J. Rossbach,DESY

## Where are we?  Progress with SASE FELs: VISA

- see:
- Tremain,Murokh
- WPPH118/122
- Wed. afternoon

- J. Rossbach,DESY

## Where are we?  Progress with SASE FELs: LEUTL

- J. Rossbach,DESY

## Where are we?  Progress with SASE FELs: LEUTL

**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/ANL
- Tuesday 13:30h

- J. Rossbach,DESY

## 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.**

- J. Rossbach,DESY

## Where are we?  Progress with SASE FELs: TESLA

- TTF FEL undulator

- J. Rossbach,DESY

## Where are we?  Progress with SASE FELs: TESLA

- SASE
- gain
- >1000

- Spontaeous
- Emission x100

- TTF FEL gain
- at 108 nm vs.
- bunch charge
- By now observed
- gain >105

- J. Rossbach,DESY

## Where are we?  Progress with SASE FELs: TESLA

- J. Rossbach,DESY

## Where are we?  Progress with SASE FELs: TESLA

- FEL wavelengths reached at TTF FEL_ _

- J. Rossbach,DESY

## Where are we?  Progress with SASE FELs: Summary

_**where**__**	**__**	**__**	**__**   **__**	**__**wavelength**__**	**__**	**__**   **__**year **__**	**__**  **_
- Livermore		        	 ~1 mm		   1986
- LURE/Orsay		       	5-10 m		   1997
- UCLA/LANL	         	          	   12 m		   1998
- LEUTL/Argonne	         	  530 nm	 	   1999
- 			         	  385 nm & saturation 	   2000
- TTF FEL/DESY	     	 80-180 nm		   2000
- VISA/BNL/LLNL/SLAC/UCLA    845 nm saturation	   2001
- 				  (+2nd+3rd Harmon.)

**All observations agree with **
**theoretical expectations/computer models**

- J. Rossbach,DESY

## Where do we want to go?

- SASE FEL projects under progress:
- 			        _min. wavelength_
- APS/LEUTL	Phase2		120 nm
- APS/LEUTL	Phase3	 	  51 nm
- DESY: TTF FEL Phase2        	    6 nm		2003/2004
- SPring8: 			 ~ 5 nm  		- 2005

- SASE FEL projects proposed:
- SLAC:  LCLS			 0.15   nm	2006
- DESY: TESLA XFEL		 0.085 nm	2010

- J. Rossbach,DESY

## Where do we want to go?		Brilliance

- Peak brilliance

- Average brilliance

- LCLS
- multibunch

- LEUTL

- TTF FEL

- J. Rossbach,DESY

## Where do we want to go?		LCLS

- J. Rossbach,DESY

## Where do we want to go?		LCLS

- SLAC linac tunnel

- undulator hall

**Linac-0**
*L*6 m

**Linac-1**
*L*9 m
**rf 38°

**Linac-2**
*L*330 m
**rf 43°

**Linac-3**
*L*550 m
**rf 10°

**BC-1**
*L*6 m
*R*56 36 mm

**BC-2**
*L*24 m
*R*56 22 mm

**DL-2**
*L*66 m
*R*56 = 0

**DL-1**
*L*12 m
*R*56 0

- undulator
*L*120 m

- 7 MeV
***z * 0.83 mm
***** * 0.2 %

- 150 MeV
***z * 0.83 mm
***** * 0.10 %

- 250 MeV
***z * 0.19 mm
***** * 1.8 %

- 4.54 GeV
***z * 0.022 mm
***** * 0.76 %

- 14.35 GeV
***z * 0.022 mm
***** * 0.02 %

*...existing linac*

- new

**RF**
**gun**

- 25-1a
- 30-8c

- 21-1b
- 21-1d

- 21-3b
- 24-6d

- X

**Linac-*****X***
*L*0.6 m
**rf=

- Producing short bunches for LCLS

- J. Rossbach,DESY

- Damping Ring (**  30 **m)

- 1.5%

- Short Bunch Generation in the SLAC Linac

- Compress to 80 fsec in 3 stages

- P. Emma et. al., **FPAH165**

**New proposal for:**
*LCLS* accelerator optics R&D
- Ultra-short *x*-ray science program at ***SLAC***

- J. Rossbach,DESY

## Where do we want to go?		TESLA

- TESLA scheme

- J. Rossbach,DESY

## Where do we want to go?		TESLA

- Beam switchyard
- distributing the electron bunch trains to various undulators

- J. Rossbach,DESY

## Where do we want to go?		TESLA

- J. Rossbach,DESY

## Where do we want to go?		TESLA

- A potential site for TESLA near Hamburg

- J. Rossbach,DESY

## 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!

- J. Rossbach,DESY