X-ray Free Electron Laser
Part-1 Accelerator PartXFEL Research & Development Division
RIKEN SPring-8 Center
Hitoshi Tanaka

2013/09

Cheiron School 2013

1Outline
1. Introduction –What we can observe using
XFEL
2. Overview of SASE XFEL
3. Approach to compact XFEL
4. Performance of XFEL

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Remarkable Features of XFEL

Degree of Coherence（％）• High Peak Brilliance (~1033)• Narrow Pulse Width (~10 fs)• High Degree of Coherence (~100 %)100×1031010-15
10-14

110-13
10-12

0.1
0.01

10-11

SPring-8

10-10×101010

3Photon Factory10201030
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XFEL

Cheiron School 2013

×1093

1. What XFEL enables us to observe
Coherence
Structure analysis on non-crystalline material (e.g., amorphous,single particle)
Ultrafast
Structure/Electric properties probed with fs temporal resolution(e.g. ultrafast phase transition)
Peak BrilliancePhysics in highly-excited/extreme state under ultra-intense
optical field (e.g. high density state)

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1. Introduction –What we can observe using
XFEL
2. Overview of SASE XFEL
3. Approach to compact XFEL
4. Performance of XFEL

2013/09

Cheiron School 2013

5

SASE XFEL Scheme
Stimulated Radiation
電子銃E-Gun

Electron
BeamUndulator

Linac

MicroBunching
Coherence
Large

Spontaneous

Log Power

SASEPower
Saturation

Coherence
Small

Undulator Length
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Free electrons as a laser medium
Resonance
condition
Electron beam is trapped in an electro-magnetic potential andthis potential generates energy modulation around the stable
fixed point. Then the energy modulation is converted to density
modulation through the energy dispersion of the undulator.

λ2013/09

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Free electrons as a laser medium
Instead of stimulated emission, the density
modulated electrons with an interval of a resonancewavelength λ , enables laser amplification.
- Independent on energy level in atoms and molecules -Let’s estimate λ assuming
λu=15mm, K=2,γ=3915@2GeV

λ = 1.5 nm

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Single pass laser system removing an opticalcavity requires highly brilliant electron beam +long undulator with a large number of periods＜Brilliant electron beam＞
High electron density achieving a high gain andlow angular divergence keeping density
modulation of Å order.

＜Long undulator＞
A larger number of periods realizes asufficiently high gain by a single pass, whichcorresponds to that obtained by the opticalcavity system.
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Laser Amplification Gain

Normalized emittance at a lasingpart

For the higher gain,
smaller emittance, higher
beam current required
Peak current
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Laser Amplification GainλSASE=1Å, K=1.85, λu=18 mm, E=8 GeV, Ip=3 kA,∆E/E=4x10-5, βave~30m,

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Cheiron School 201311

Laser Amplification GainλSASE=1Å, K=1.85, λu=18 mm, E=8 GeV, Ip=3 kA,∆E/E=4x10-5, βave~30m,

For the higher laser
power, accurate
overlap between laser
field and electron
beam along a certain
distance, 15 to 25 m

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Shortening laser wavelength by high energy
electron beam + short-period undulators＜High energy electron beam＞
Undulator radiation wavelength depending on the
inverse of gamma square＜Short period undulators＞
Undulator radiation (laser) wavelength being
proportional to the undulator period

2013/09Cheiron School 201313

1. Introduction –What we can observe usingXFEL
2. Overview of SASE XFEL
3. Approach to compact XFEL
4. Performance of XFEL

2013/09

Cheiron School 201314

Future Perspective
Although variety of XFEL applications areexpected, one facility can provide only afew BLs.
To widely utilize XFEL, it is essential to
make the facility scale compact as muchas we can. World’s trend goes to thisdirection as XFEL usefulness becomes
gradually clear.
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Leading three XFELSASE XFELs under operation &construction in 3-sites

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Development Target
SPring-8 Compact SASE Source(SCSS) Concept
Compact , cheaper,
but high-performanceversus2013/09

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Wavelength of undulator radiation r

To generate X-ray with lower beam energy
requires a shorter undulator period andsmaller K-value

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Design Concept of SPring-8 Compact SASE
Source (SCSS)
Lower Beam Energyr

Short period
in-vacuum
undulator

Size Reduction

Efficient Acceleration
Further Size Reduction

C-band highgradientacceleration
system+Smaller K

Smaller Normalized
Beam Emittance
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Cheiron School 2013

Themionicgun based
low emittanceinjector
19

BC3 out

Peak current (A)Peak current (A)BC2 out

Beam energy (MeV)

Beam energy (MeV)

BC1 out

Peak current (A)Beam energy (MeV)

Injector out

Peak current (A)Beam energy (MeV)

Compact design for 8-GeV SASE XFELLow emittance injector
with CeB6 E-gun

Laser system forwavelength compression

C-band accel.
systemShort-period
In-vacuum undulators~700 m2013/09

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Design Performance of XFEL
Comparison with SPring-8 performance
Parameter• Wavelength(fundamental）• Pulse Duration• Repitition
MHz• Spatial Coherence• Peak Power• Peak Brilliance• Averaged Brilliance

XFEL
SPring-8>0.06 Å >0.05 Å<100 fs~40 ps< 60 Hz~40
100%~0.1%
20~30 GW 100~200 W~1034~1024~1022~1021

Def of Brilliance：phs/sec/mrad2/mm2
XFEL/SPring-8 Beamline Technical Design Report Ver. 1.0, June 17 (2008)2013/09

Cheiron School 201321

1. Introduction –What we can observe using
XFEL
2. Overview of SASE XFEL
3. Approach to compact XFEL
4. Performance of XFEL

2011/09

Cheiron School 201322