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

X-rayy Free Electron Laser
Part-1 Accelerator PartXFEL Research & Development Division
RIKEN SPring
SPring-8
8 CenterHitoshi Tanaka

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1

1. What XFEL enables us to observe
1Keyy words
Brilliance(X109)XFEL
Coherent((100%intransverse)

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1. Introduction –What we can observe using
XFEL
2. Overview of SASE XFEL
3 Approach to compact XFEL
3.
4. Performance of XFELUltrafast( 10 fs)(~10f )

3

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Free electrons as a laser medium

SASE XFEL Scheme
Stimulated Radiation
E電子銃
E-GunGun

ElectronBeam

Resonance
condition

Undulator

Linac

MicroBunchingB
hi
Coherence
Large

Spontaneous

Log PowerSASE

λ = λu − vzT ≈⎞λu ⎛ K 2eBλu
2 21++γθ⎜⎟⎟, K =⎜22πm0 cγ22γ ⎝⎠

Electron beam is trapped in an electro
electro-magnetic
magnetic potential andthis potential generates energy modulation around the stablefixed ppoint. Then the energy
gy modulation is converted to density
ymodulation through the energy dispersion of the undulator.

PowerSaturation

λCo e e ce
Coherence
Small

Undulator Length
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Laser Amplificationp
GainFree electrons as a laser medium
Instead of stimulated emission, the density
modulated electrons with an interval of a resonancewavelength λ , enables laser amplification.
‐ Independent
pon energy
gy level in atoms and molecules ‐L1G =ωu =2

K22(1 + K 2 )2πcλu,

ne =Neσ lσ xσ y.

,Normalized emittance at a lasingpart⎛ β ε ⎞1/ 3
For the higher gaingain,ns⎟⎟
L1G ∝ ⎜⎜smaller emittance, higher⎝ Ip ⎠beam current requiredLet’s
Lets estimate λ assuming
λu=15mm, K=2,γ=3915@2GeV

λ = 1.5 nm

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λu,4 3πρF1(K ) = ( J 0(ξ ) − J 1(ξ )) , ξ =⎞λ ⎛ K2
λ = u2 ⎜⎜1 ++ γ 2θ 2 ⎟⎟, K ≅ 1 ~ 222γ ⎝⎠2012/9/28

6Peak current
7

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

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

Lg (m)

Lsat (m)

120

12.00

110
6.000
100
90.0

Lg
g (m)

4.000

70.0
60.0

3.000
50.0
2.000
0.4

0.6

0.8

1

1.2

1.4

40.0
1.6

4 10-4

3.6 108.000-4

3.4 10-4
3.2 10-44

6.000

3 10-4
4.000

2.000
0.4

2 8 10-44
2.8

0.6

0.8

1

1.2

1.42.6 10-4
1.6

Norm emitt (mmmrad)
Norm.emitt

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9Removingg opticalpcavity
y systemyby
y highlyg ybrilliant electron beam + long undulator with alarge number of periods

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10Shorteningg laser wavelength
g byy highg energygyelectron beam + short-period undulators

Undulator radiation wavelength depending on the
inverse of gamma squareHigh electron density achieving a high gain andlow angular divergence keeping density
modulation of Å order.

＜Short period undulators＞
Undulator radiation (laser) wavelength being
proportional to the undulator period＜L＜Longundulator＞
d l t ＞
A larger number of periods realizes asufficiently
ffi i tl hihighh gaini b
by a single
i l pass, whichhi hcorresponds to that obtained by the opticalcavity
it system.
tCheiron School 20122012/9/28＜High energy electron beam＞＜Brilliant electron beam＞

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

3.8 10-4
10.00

Norm emitt (mmmrad)
Norm.emitt

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ρPsat (GW)

ρ (-)

80.0

Lsat (m)5.000Laaser Power att Saturation (GGW)

7.000

Laser Amplification
pGain

11

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

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Although
Althh variety
i t off XFEL applications
li tiareexpected , one facility can provide only afew BLs.
To widelyT
id l utilize
tili XFEL,XFEL it iis essential
ti l tto
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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Development Target

Leading three XFELSASE XFELs under operation &construction in 3-sites

SPring‐‐8 Compact SASE Source
SPring(SCSS) Concept
Compact , cheaper,
but highhigh--performanceversus2012/9/28

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Designg Concept
p of SPring-8g Compact
pSASESource (SCSS)

Wavelength of undulator radiation r⎞λu ⎛K22 2λ=+ γ θ ⎟⎟⎜1 +2⎜22nγ ⎝⎠Short period
in-vacuum
undulator

Lower Beam Energyr
Size Reduction

C-band highgradientacceleration
systemEfficient Acceleration

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

Further Size Reduction+Smaller
K
Smaller Normalized

Themionic
gun based
low emittanceinjector

Beam Emittance
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BC3 out

Low emittance injector
with CeB6 E-gun

Laser system forwavelength compression

C-band accel.
systemShort-period
In-vacuum undulators~700 m2012/9/28

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Design Performance of XFEL
Comparison with SPring-8 performance

Peak current (A)Peak current ((A)

BC2 out

Beam energy (MMeV)

Peak current ((A)

BC1 out

Beam energy (MMeV)

Peak current (A)Injector out

Beam energy (MMeV)

Beam energy (MeV)

Compactp
designg for 8-GeV SASE XFEL

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Parameter• Wavelength(fundamental）• Pulse Duration• Repitition
MHz• Spatial Coherence• Peak Power• Peak Brilliance• Averaged Brilliance

XFEL
SPring-8>0.06
0.06 Å >0.05
0.05 Å<100 fs~40 ps< 60 Hz~4040
100%~00.1%1%
20~30 GW 100~200 W~101034~101024~1022~1021

Def of Brilliance：phs/sec/mrad2/mm219

XFEL/SPring-8 Beamline Technical Design Report Ver. 1.0, June 17 (2008)2012/9/28

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

2012/9/28

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