1. Compton X-ray generation in a small S-band accelerator
~ LUCX Project at KEK-ATF ~
Collaborators
KEK-ATF:
S. Araki, M. Fukuda, Y. Higashi, Y. Honda,
T. Taniguchi, N. Terunuma, J. Urakawa, S. Liu
WASEDA University:
K. Sakaue, M. Washio
KYOTO University:
N. Sasao, H. Yokoyama
TOKYO University:
H. Sakai
POSIPOL 2007 Workshop, May 2007, LAL, Orsay, France
25 May 2007
POSIPOL 2007

2. Contents Introductionｓ
Laser Undulator Compact X-ray Source (LUCX) in KEK-ATF
Control System of the LUCX
Multi-bunch Beam Operation
LUCX X-ray Source
Conclusions
25 May 2007
POSIPOL 2007

3. Introduction
Our aim is development of compact high brightness X-ray generator.
It is required from various field.
(medical diagnosis, biological sciences, etc.)
For example,
K-edge digital subtraction angiography.
Angiography is a procedure that enables blood vessels to be visualized using the absorption by Iodine at 33keV
XCOM: Photon Cross Section Database
25 May 2007
POSIPOL 2007

4. X-ray generation
We have developed an X-ray source based on Inverse Compton Scattering with a pulsed laser-wire Cavity.
=> LUCX (Laser Undulator Compact X-ray source) project.
Pulsed Laser Cavity
43 MeV
43 MeV
Parameter :
Cavity Length: 420 mm
Mirror Curvature radius: 250mm
Finesse 1500
Enhancement factor ~ 780
l = 1064 nm (1.17eV)
6W (17nJ/pulse)
25 May 2007
POSIPOL 2007

5. Merit Compact and Inexpensive Laser system is compact.
Merit of the X-ray source using Inverse Compton Scattering
X-ray source using an undulator at a GeV order storage ring.
High intensity, High stability
but, in general, large amount of money and huge facilities.
X-ray source based on Inverse Compton Scattering
X-rays can be produced by lower energy e- beam.
The ring can be downsized.
Compact and Inexpensive
But, we need to demonstrate the method.
Merit of the pulsed laser-wire cavity
No amplifier system.
Laser system is compact.
But, difficult to raise finesse of Laser cavity.
25 May 2007
POSIPOL 2007

6. Place of the accelerator for LUCX project
The accelerator for LUCX project is constructed in ATF building //
Here
25 May 2007
POSIPOL 2007

7. LUCX Layout Energy 43 MeV Intensity 200nC/train
Number of Bunch 100 bunches/train
Bunch spacing ns
Rep. Rate Hz //
25 May 2007
POSIPOL 2007

8. Current Beam line
We plan to demonstrate the X-ray generation with the pulsed LW Cavity.
Adding an accelerating tube to upgrade the beam energy.
Current beam line
e- beam
Collision point
UV: 3mJ/bunch
X-ray
solenoid
Compton
S-band accelerating tube (3m)
X-ray
detector
Bending
magnet
Q-magnet
Q-magnet
Q-magnet
RF Gun
Chicane
Cathode: Cs-Te
An electron beam is accelerated
Second phase
Number of Bunch 100 bunches/train -
Energy 43 MeV (Design) -
Intensity 200nC/train (Design) : 50nC/train (MAX)
Bunch spacing ns
Rep. Rate Hz -
100-bunch electron beam is accelerated to 43 MeV.
with 50nC /train charge generates.//
25 May 2007
POSIPOL 2007

9. Photo cathode RF gun Q.E. : ~0.3%
RF gun cavity
(1.6cells)
Solenoid
RF gun Cu
UV laser
266nm
e- beam
Cs2Te
S-band
2856MHz
(BNL Gun IV)
UV laser /
Q.E. : ~0.3%
RF Gun
Mo Cathode plug
RF processing is continued from April (about 400 hours)
25 May 2007
POSIPOL 2007

10. RF system Dummy Load S-band 2856MHz 25 May 2007//
25 May 2007
POSIPOL 2007

11. Beam monitor Collision point Emittance measurement
Faraday Cup
Top view
BPM
BPM
ICT
BPM
BPM
solenoid
PRM
PRM
S-band accelerating tube (3m)
RF Gun
PRM
PRM
Bending
magnet
Q-magnet
Q-magnet
Cathode: Cs-Te
Q-magnet
Chicane
e- beam
However, these monitors ware transposed to LW chamber.
Emittance measurement
Side view
ICT & Faraday Cup: Beam current monitor
PRM
BPM: Beam position monitor
BPM
ICT
PRM: Beam Profile Monitor
OTR target or Al2O3 (Cr3+ doped)
Beam energy and energy spread measurement
25 May 2007
POSIPOL 2007

12. Schematic Diagram of the Control System
EPICS device support for network device !! # use Ethernet as a field-bus
CAMAC (Toyo / CCNET [PC/104+] )
PLC (Yokogawa / FA-M3, Keyence / KV-1000)
Data Logger (Yokogawa / DARWIN)
Main PC is running a sequencer program for automatic RF-conditioning.
A usual desktop PC is here. It’s running Linux-EPICS.
An IOC program, MEDM displays and a Channel Archiver are running on the PC.
This IOC program talks to a PLC. It’s a modulator controller.
And there is PLC one more. ( It’s a KV-1000 made by KEYENCE. Co. )
We use this for a flow-meter monitor and interlock and screen monitor control.
We have another PC, It’s single board computer, which is embedded in this CC/NET,
a special intelligent CAMAC controller.
Another IOC program is running on this CC/NET to measure the pressure and to control the magnets.
Then, This is another CCNET, and for the beam monitor.
Some monitors in the shield were done by using Looger.
Temperature and the voltage measured it by using the Data LOGGER.
The laser mirror and shutter was connected at RS232c.
We have much 232c and GPIB.
They are connectable with a network using an Ethernet converter.
(LW)These will be completed in the near future. <?
And a few controllers //
-Main PC is running a sequencer program for automatic RF-conditioning.-
It’s the main purpose of this control system.
25 May 2007
POSIPOL 2007

13. Beam operation Energy: 40MeV (operation) Intensity: 50nC/train (MAX)
We have started beam operation from July 2006.
The multi-bunch beam could be transported to the beam dump.
Energy: 40MeV (operation)
Intensity: 50nC/train (MAX)
Number of bunch: 100 bunches
~1MeV
25 May 2007
POSIPOL 2007

14. Emittance measurement
Collision point
εx: 3.0 [mm・mrad]
QF1
QD1
Beam current : 2.5nC/train, 5bunches
Beam profile
at Collision point
εy: 4.7 [mm・mrad]
σx: 86um
σy: 36um
CP1G
(OTR)
25 May 2007
POSIPOL 2007

15. Beam loading (simulation)
Black line: without beam loading
Blue line: with beam loading
Input RF pulse
Laser injection timing
Beam Energy [MeV]
100bunches (280ns)
Energy difference is within 1%
at the laser injection timing
of 3.7ms.
The energy difference that two lines show is large.
Mathematica simulation
x‐axis is Laser injection timing, u-sec. y-axis is Beam energy, //
Time [ msec ]
25 May 2007
POSIPOL 2007

16. Beam loading measurement
e- beam
BPM7
(PPM5)
ICT2
MS4G: Beam profile monitor
MS4G
(OTR) E大
0.9MeV/c E小
25 May 2007
POSIPOL 2007

17. Compensation for Beam loading
50nC/100bunches
Momentum vs Laser injection timing(5bunches)
(3)
(3)
(1)
(2)
280ns (100 bunches)
Energy diff of bunches = 0.4MeV/c
(2)
set here
(1)
This shows is plot of Momentum vs Laser injection timing.
A horizontal axis 0 corresponds to 3.5 u-seconds.
The timing which puts a beam is changed with (1), (2), (3),
and is measured
25 May 2007
POSIPOL 2007

18. Operation Energy 43MeV 40MeV
Intensity 200nC/train (Design) 30 ~ 50nC/train
Number of Bunch 100 bunches/train -
Bunch spacing ns -
Rep. Rate Hz -
Collision point
Faraday cup
Top view
BPM
BPM
ICT
BPM
BPM
solenoid
PRM
S-band accelerating tube (3m)
RF Gun
PRM
PRM
Bending
magnet
Q-magnet
Q-magnet
Cathode: Cs-Te
Q-magnet
Chicane
e- beam
We have a 2 ICT ,
And 5 BPM,
And 5PRM,
And we installed LW chain bar.
P: 40 MeV (1.5nC, 5bunches)
sP/P : 0.15%
0.4MeV/c
Side view
PRM
Momentum spread
BPM
ICT
Momentum difference
25 May 2007
POSIPOL 2007

19. X-ray generation (LUCX)
We started to demonstrate the X-ray generation with Pulsed Laser.
Collision angle is 20o in order to get as much intensity as possible.
Head-on collision is best, but the e- beam will collide with the mirror.
We started to demonstrate the X-ray generation with Pulsed Laser Cavity.
Collision angle is 20o in order to get as much intensity as
Head-on collision is best, but the e- beam will collide with the mirror.
Maximum X-ray energy is 33 keV.
25 May 2007
POSIPOL 2007

20. LUCX-Required Spec. of Optical Resonator [ pulsed laser-wire ]
Initial Laser :
Cavity Length : 420mm
Beam Waist : <170um in 2s
Mirror Curvature : <250mm
Finesse : >1550
Mirror Reflectivity : 99.7%, 99.9%
Cavity Transmission
We have a 6W pulse laser,
We have finished the test of an optical resonator.
It’s long keep on ~10 hour.
FB ON
(Loop Close)
T. Jitter = 3ps
Error signal
25 May 2007
POSIPOL 2007

21. Optical Circuit P-LW-CAV installed in APR2007. e- beam e- beam
We installed P-LW-CAV of the LUCX by the end of last month.
25 May 2007
POSIPOL 2007

22. Optical Resonator R/D ~Preparation of install resonator~
Shutter speed = 10sec
Optical Resonator R/D ~Preparation of install resonator~
After several studies to characterize and reduce the jitters, we decide to install the resonator to LUCX accelerator.
The parameter of pulsed laser-wire is as follows.
Frequency
Finesse
Waist Size
(2)
Inject laser power
Laser power in resonator with FB
357 MHz
1889 ±31.5
178.4 ±7.5 mm
4.05 W @357 MHz
2.40 ±0.05 kW
x 630
Inside of e-beam chamber was photocopied by Dig-CAM.
(Purge with Nitrogen)
25 May 2007
POSIPOL 2007

23. Expected number of X-rays
Laser (in LWC)
 = 1064 nm (1.17eV)
2.8 mJ /bunch
1.5x1013 photons/bunch
s = 89 mm
10ps
e- beam
43 MeV
0.5nC/bunch
3.1x109/bunch
sx, sy = 80mm, 40mm
10ps
100 bunches/train
12.5 Hz
Energy
Intensity
Beam size
Pulse width
Number of bunch
Rep. Rate
< 5mrad,
>= 27 keV
In view of the acceptance (< 5mrad),
Expected number of X-rays
2 x 104 photons/sec
(1.6 x 103 photons/train)
25 May 2007
POSIPOL 2007

24. Collision Study of BG and the collision experiment were begun.
[18MAY2007 ~] Just experiment now under going.
Since BG signal is large.
Sorry! No data shown to you…
View of the transmitted laser
25 May 2007
POSIPOL 2007

25. Conclusion
We plan to demonstrate X-ray generation with Pulsed LW Cavity.
To upgrade the beam energy, an accelerator tube was installed. ◯ ◯
We have built a fully-PC/Linux-based control system with EPICS for LUCX operation.
After 400 hours processing, we start the beam operation.
The multi-bunch beam (50nC/train, 100bunches) can be transported to the beam dump. ◯
We need to continue the rf processing to increase the beam energy
and the beam charge and also to optimize the parameter (emittance, energy spread, solenoid current, etc) . ◯ ◯
The pulsed laser-wire cavity was installed. First step is to observe a signal of an X-ray.
25 May 2007
POSIPOL 2007

26. Thanks for your attention!
25 May 2007
POSIPOL 2007

27. …
25 May 2007
POSIPOL 2007

28. !Previous beam line Until Nov 2005, RF gun study was done
for generating a high intensity multi-bunch beam.
Previous beam line
e- beam
UV: 3mJ/bunch
solenoid
RF Gun
Q-magnet
Chicane
Cathode: Cs-Te
Faraday cup
First phase
100 bunches
Energy MeV
Intensity nC/train
Number of Bunch 100 bunches/train
Rep. Rate Hz
K. Hirano, et al. “High-intensity multi-bunch beam generation by a photo-cathode RF gun”, Nucl. Instr. and Meth. A560, pp (2006).
25 May 2007
POSIPOL 2007

29. !Beam Optics Collision point e- beam
Beam size at the collision point: sx 64 mm
sy 32 mm
Beam size is less than 3mm to avoid the BG signal caused by beam loss.
25 May 2007
POSIPOL 2007

30. !Laser system (Gun) To gun Pockels cell(KD*P):
Pulse width ≦ 280ns (100bunches)
Fourth Harmonic Generation: Two BBOs,
Conversion efficiency ~ 25% (IR -> UV)
266nm
PC1
PC2
Seed laser
To gun
TBP, 357MHz mode-locked pulse laser
Nd:YVO4 (λ:1064 nm, FWHM:9 ps)
Two amplifier heads (Continuum, rod: Nd:YAG)
Double pass configuration
Gain ~ 2000
25 May 2007
POSIPOL 2007

31. !Laser system (Gun) UV: 3uJ/pulse Spatial filter Pin hole: d=20um
Telescope (f=+50mm, +50mm)
Telescope (f=+300mm,-150mm)
Intensity controller (half wave & PBS)
UV: 3uJ/pulse
25 May 2007
POSIPOL 2007

32. !RF phase (Gun) Momentum spread vs laser injection phase Phase plot
σP/P [%]
Beam current [a.u.]
LaserをGunに入射する Gun RF phase をスキャン。エネルギー広がりが最小の場所にセット
σP/P :Minimum
Laser injection phase [deg]
Laser injection phase [deg]
25 May 2007
POSIPOL 2007

33. ! Momentum spread vs RF phase (Accelerator)
Momentum vs RF phase (Acc.)
e- beam
Momentum P [MeV/c]
MS4G
1.5nC, 5bunches
Momentum spread vs RF phase (Acc.)
Min: 0.15%
P: 34 MeV
σP/P : 0.15%
σP/P [%]
25 May 2007
POSIPOL 2007

34. !Optical Resonator R/D ~Problems of Optical Resonator~
Width of resonance peak
We should control
the resonator length <0.1nm
Gain=1000
Peak width (FWHM)<0.2nm
No jitter is permitted!!
Where are the jitters come from?
>Mode-locked laser FB
Timing stabilizer FB causes a jitter
>Acoustic noises
1~2kHz acoustic jitter appears
25 May 2007
POSIPOL 2007

35. Optical Resonator [PLL] ~ Analog circuit
Transmission Measurement結果
　Mirror1 : T=0.221±0.004%
　Mirror2 : T=0.071±0.001%
Lossを”0”として1-Tの値からReffを算出すると、
Reff=99.85%　(Finesse測定による結果 Reff=99.83%)
[PLL] ~ Analog circuit
Timing Error ⇒(FB) Laser Piezo
Timing Error ⇒(FB) Cavity Piezo (FF) Laser Piezo
Tilt Locking kept a long time. ~10h
25 May 2007
POSIPOL 2007

36. !Tilt Locking Test FBが落ちる瞬間を モニターする。 Timing Errorが 大きく変化して
Piezoが大きく動き、
FBが外れる。
⇒FBが外れるときのほとんどが、Timing Errorが原因。
25 May 2007
POSIPOL 2007