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

2014/9	Cheiron	  School	  2014	

1	Outline	
1. Introduction –What we can observe using
XFEL
2. Overview of SASE XFEL
3. Approach to compact XFEL
4. Performance of XFEL	  2014/9	

Cheiron	  School	  2014	

2	Remarkable Features of XFEL

Degree of Coherence（％）	

• High Peak Brilliance (~1033)• Narrow Pulse Width (~10 fs)• High Degree of Coherence (~100 %)100×1031010-1510-14

110-13
10-12

0.1
0.01

10-11

SPring-8

10-10×10-­‐3	  1010（Ph2014/9	

XFEL	  Photon Factory

1020
oton Peaks/sec/mmB2 rillian/mra ce
d 2/0.1％
b1030×109.w.）	

Cheiron	  School	  2014	

3	

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 Brilliance	Physics in highly-excited/extreme state under ultra-intense
optical field (e.g. high density state)	

2014/9	Cheiron	  School	  2014	4	

1. Introduction –What we can observe using
XFEL
2. Overview of SASE XFEL
3. Approach to compact XFEL
4. Performance of XFEL	  2014/9	

Cheiron	  School	  2014	

5	

SASE XFEL Scheme	Stimulated Radiation	

ElectronBeam

Undulator

Linac

MicroSpontaneous Bunching
Coherence
Log PowerLarge		

SASE

Power
Saturation	
Gain
104 ~ 105

電⼦子銃
E-Gun

Coherence
Small	

Undulator Length	
2014/9	Cheiron	  School	  2014	

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To work optical cavity-free system we need“highly brilliant electron beam” and “ longundulator with a large number of periods”	
＜Brilliant electron beam＞
High electron density achieving a high gain and low
angular divergence keeping density modulation of Å
1 m – 0.5Å	order.	
10 urad	
10 um	＜Long undulator＞	
A larger number of periods realizes asufficiently high gain by a single pass, whichcorresponds to that obtained by the opticalcavity system.
2014/9	Cheiron	  School	  2014	

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Long undulator comprising of 18 segments has
To behave as a single undulator	
For this purpose,•18 segments with identical performances （single color）•Undulator segments alignment（alignment of squares）•Straight e-beam trajectory（black straight line）

by beam based tuning	

2014/9	Cheiron	  School	  2014	8	

To access short laser wavelength we need“high energy electron beam” , “appropriate
period undulators” and large K-value	
＜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

2014/9	Cheiron	  School	  2014	

9	Free electrons as a laser medium	
Resonance
condition	

*λu 'K2eBλu
2 2λ = λu − vzT ≈ 2 ))1 ++ γ θ ,,, K =22πm0 cγ2γ (+Electron beam is trapped in an electro-magnetic potential andthis potential generates energy modulation around the stable€ Then the energy modulation is converted to density
fixed point.
modulation through the energy dispersion of the undulator.	

λ	2014/9	

Cheiron	  School	  2014	

10	Free electrons as a laser medium	
Developing density modulation	
Undulator	  Field	  ve	  z	  Ex	  EM	  Field	  by	  RadiaAon	  Ex	  ve	  Electron	  Orbit	  ve	  Ex	  2014/9	Cheiron	  School	  2014	

11	Free electrons as a laser medium	

Instead of stimulated emission, the density modulatedelectrons with an interval of a resonance wavelength
λ , enables laser amplification.
-­‐	  Independent	  on	  energy	  level	  in	  atoms	  and	  molecules	  -­‐	(λu %K22 2
λ = 2 ''1 ++ γ θ **, K ≅ 1 ~ 222γ &)Let’s estimate λ assuming
λu=15mm, K=2,γ=3915@2GeV

λ = 1.5 nm	
2014/9	Cheiron	  School	  2014	12	Laser Amplification Gain	
L1G =

λu
4 3πρ

,&K
ρ =(' 4γ

F1(K )

2F1(K ) = ( J 0(ξ ) − J 1(ξ )) , ξ =€€€2Ω ρ )32πcωu =,λu+ ,ωu *K

222(1 + K ),ne =Ne.
σ σ xσ y1)2& 4 πc 2 r ne eΩ ρ = ((++ ,γ'*€ emiKance	  at	  a€Normalized	  	  lasing	  part	  1/ 3% βε (ns**L1G ∝ ''& Ip )€For the higher gain,
smaller emittance, higher
beam current required	

Peak	  current	  	  2014/9	

Cheiron	  School	  2014	

13	

Laser Amplification Gain	
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 (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

ρ

4 10-4
3.8 10-4

10.00

3.6 10-4
8.000

3.4 10-4
3.2 10-4

6.000

3 10-4
4.000

2.000
0.4

2.8 10-4
0.6

0.8

1

1.2

1.4

2.6 10-4
1.6

Norm.emitt (mmmrad)

Norm.emitt (mmmrad)

2014/9	Psat (GW)

Cheiron	  School	  2014	

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ρ (-)

80.0

Lsat (m)5.000

Laser Power at Saturation (GW)

7.000

Laser Amplification Gain	
λSASE=1Å, K=1.85, λu=18 mm, E=8 GeV, Ip=3 kA,
ΔE/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	

2014/9	Cheiron	  School	  2014	

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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	  2014/9	

Cheiron	  School	  2014	

16	

Future Perspective	
Although variety of XFEL applications areexpected , one facility can provide only afew BLs.	
To widely utilize XFEL, it is essential tomake the facility scale compact as muchas we can.	  World’s trend goes to thisdirection as XFEL usefulness becomes
gradually clear.	
2014/9	Cheiron	  School	  2014	

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Leading three XFEL	SASE XFELs under operation &construction in 3-sites	
LCLS@SLAC(2010~)“!"#!$%&''”
Euro-XFEL (2014~)
High rep rate

~3.4 km	

~2 km	XFEL@SPring-8 (2012~)
Compact

0.7km	
5

2014/9	Cheiron	  School	  2014	

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Development Target	SPring-­‐8	  Compact	  SASE	  Source	  	  (SCSS)	  Concept	  	  SCSS	  Compact , cheaper,
but high-performanceversus

LCLS/FLASH	  2014/9	Cheiron	  School	  2014	19	

Wavelength of undulator radiation,	2%(λuK2 2λ=1++γ
θ'*'*222nγ &)To generate X-ray with lower beam energy 		requires a shorter undulator period andsmaller K-value	
K-value 	

2014/9	Cheiron	  School	  2014	

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

Short period
in-vacuum
undulator	

Size Reduction	

Efficient Acceleration	
Further Size Reduction	

+SmallerK	
Smaller Normalized

Beam Emittance	
2014/9	Cheiron	  School	  2014	

C-band highgradientacceleration
system	Themionicgun based
low emittanceinjector	
21	

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 XFEL	Low emittance injector
with CeB6 E-gun

3-stage bunch
compressor

C-band accel.
systemShort-period
In-vacuum undulators~700 m2014/9	Cheiron	  School	  2014	

22	

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

XFEL
SPring-8	>0.06 Å>0.05 Å<100 fs~40 ps< 60 Hz~40 MHz
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) 	
2014/9	Cheiron	  School	  2014	

23	

1. Introduction –What we can observe using
XFEL
2. Overview of SASE XFEL
3. Approach to compact XFEL
4. Performance of XFEL	  2014/9	Cheiron	  School	  2014	

24	

History of SACLA	
2006~2010 XFEL construction
2011 Feb. 21 Beam commissioning started
Jun. 7 First lasing at 0.12 nm
achieved
Oct.
SASE power saturationachieved at 0.12 nm
2012 Mar. 1 User experiments officially started
2013 Apr.
2-Color SASE released to user experiments
Oct.
SASE intensity beyond 0.5 mJ/pulse achieved
Nov. First experimental symptom of seeding observed
2014 Apr.
Circularly-polarized SASE released to userexperiments
2014/9	Cheiron	  School	  2014	

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Summary of Present Performance	
Pulse Energy*:
Peak Power*:
Intensity Fluctuation*:
Lasing Wavelength:
Spatial Coherence:
Repetition:
Mean Fault Interval:
Recovery time:
Operation mode:
Reproducibility:

Sub-m J, ~0.6mJ@10keV>60 GW (e-beam, <10 fs inFWHM)~10% (σ）
0.83 - 2.8 Å (user operation)nearly full
30 Hz（Max.60 Hz）
30~40 min
1 min.
24 hr continuous~70% of the peak*It	  depends	  on	  the	  condiAon	
2014/9	Cheiron	  School	  2014	

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Evolution of SASE Intensity	

2014/9	Cheiron	  School	  2014	

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Gain Curve	
Log Scale	

Linear Scale	

Lg~2.3 m	

2014/9	Cheiron	  School	  2014	

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Laser Intensity vs Wavelength(old data)	

2014/9	Cheiron	  School	  2014	29	Laser Stability	
Laser availability in user experimental run is beyond 90%	@10 keV	

About 8 hr	

0.6 mJ/puse	

2014/9	Cheiron	  School	  2014	30	

2-Color SASE Routinely Available	• Wavelength separation of up to 30%• X-ray wavelength region• Precise delay control with an attosecond resolution 	

2014/9	Cheiron	  School	  2014	31	

Outline of System Upgrade	
0.5 MeV
ApertureGun
476MHzCB-correction

Beam dump

Energy slit

Q-mag for dispersion
correction

7.45°

238MHzChopper

Z=0 m

3.13°

L-APS(2m×2)

Injector

P2	BC1(1.8m×2)(1.8m×24)

Z~13 m3°

Z~50 mBL1Z~120 m

P1	Undulators(4.5m×2) λu=15 mm

BL2BL3Beam dump

New	Undulators(5m×15) λu=15 mm
0.36°(R56~-7.5mm)(R56~-37mm)

P4	Switchingmagnet

BC3BC2(R56~-41mm)

8 GeV

Deflector Main C-band(1.8m×104)
cavityC-band(3m×8)SCSS

Modified YAG screen
to avoid COTR

1.41°

S-bandLB-correction

1.4 GeV

400 MeV

35 MeV

ID01-08

ChicaneID09-19

Undulators(5m×19) λu=18 mm

P3	Fast	  kicker	  magnet:	  XSBTbunch-­‐to-­‐bunch	  To SPring-8control	  of	  e-­‐beam	  Z~390 menergy	  -­‐>-­‐>	  Hara	  et	  al,	  2014/9	
Cheiron	  School	  2014	
PRST	  16,	  080701	  2013	  SR from
SPring-8

To users

ExisAng	Beam dump

Combination of
XFEL and SRExperimental hall
Z~615 m32