1. ATF Intrabeam Scattering Results
Junji Urakawa
and ATF collaboration
Contents
1) Simple Review of the Measurement Method
2) Comparison with Simulation and Theory
3) Summary
11/19/2018
DR2003, Jan. 27 at Daresbury

2. Measurement Method to get the Results
We measured the horizontal emittance in the extraction line using 5 wire scanners.
Energy spread was measured by thin screen monitor in the extraction line with large dispersion.
Vertical emittance was measured by 5 wire scanners in the extraction line, laser wire and SR interferometer in the damping ring.
X-SR monitor indicates consistent results on transverse emittance.
Bunch length has been measured by streak camera with large statistical error.
Beam lifetime measurement has evaluated the emittance ratio with some assumptions.
DR2003, Jan. 27 at Daresbury

3. Comparison Measurements Numerical Comparison with SAD
Comparison with Simulation and Theory
11/19/2018
DR2003, Jan. 27 at Daresbury

4. Measurements Laser Wire in the ring SR Interferometer
DR2003, Jan. 27 at Daresbury

5. Measurements Bunch Length by Streak Energy Spread by Screen Monitor
Camera in the Ring
Energy Spread by Screen Monitor
at the Extraction Line

6. Numerical Comparison with SAD
DR2003, Jan. 27 at Daresbury

7. Numerical Comparison with SAD
DR2003, Jan. 27 at Daresbury

8. Comparison with Simulation and Theory
DR2003, Jan. 27 at Daresbury

9. Comparison with Simulation and Theory

10. Summary
Vertical dispersion only, with (h)rms=5.6mm and ey0=4.0pm (Solid).
Coupling dominated with k=0.33% (dashes).
Coupling dominated with k=1.2%, with the Coulomb log artificially increased by a factor 1.75 (dotdash).
Same as Ex. 2 but assuming ey measurement error, i.e. adding 0.9% of the measured (and splined) ex to the calculated ey (the dots).
Following is my suggestion (intention).
Reject the artificial increase.
Beam orbit tuning, dispersion and coupling correction have to do precisely.
Beam Size Measurement has to do quickly and precisely.
Improved tools will be prepared within 3 months.
DR2003, Jan. 27 at Daresbury

11. Novel Electron-Beam Diagnostic (Laser Wire ) at St Catherine’s College, Oxford, England Junji Urakawa, KEK, Japan, July 10th 2003
1. Development of laserwire beam profile monitor based on stable Compton scattering in a Fabry-Perot optical cavity. (0.1mm(rms) position stability, 5mm(rms) beam collision.)
2. Future development
3. Conclusion
Ultra-low emittance electron beam is good for you.

12. Introduction to laserwire
motivation
Linear Colliders require nm-size beams
Damping rings produce ultra low emittance beams
ATF experiment at KEK
to demonstrate low emittance beam production
develop handling / monitoring techniques
study beam dynamics ( low emittance, multi-bunch )
ATF damping ring
beam energy :1.28 GeV
intensity : 1.2×1010 [e/ bunch]
number of bunches : single / multi (2~20bunches) (2.8ns spacing)
1.1 ×10-9 [m rad] ( horizontal emit.) ~ 100 [mm]
0.5 × [m rad] ( vertical emit.) ~ 7 [mm]
need reliable beam size monitors

13. Introduction CW laserwire with optical cavity
principle of laserwire monitor
thin photon target (laserwire) transversely placed on the beam orbit
scan across the electron beam
“count” Compton scattered photons
Important issues
high intensity
small waist size
CW laserwire with optical cavity
enhance laser power
(high mirror reflectance ⇔ high power gain )
control laser waist size
laser on/off for background subtraction

14. Introduction feature other monitors
reliable beam size monitor in Damping ring
non-invasive method
direct measurement of the beam size
dispersion negligible (straight section)
multi-bunch beam (timing detection of gamma rays)
work at almost zero current
other monitors
SR interferometer (arc)
X-ray SR monitor (arc)
wire scanner (ext)
OTR/ODR (ext)

15. Experimental setup 1. laserwire 2. detector and collimator
3. data taking system

16. Chamber system
replaced in 2002 summer shutdown
cavity module

17. Optics whole system mounted on movable table
movable both vertical/horizontal
table position is monitored by laser position sensor

18. Laserwire setup
vertical wire
horizontal wire

19. Cavity resonance power inside cavity Fabry-Perot high power gain
⇔narrow resonance

20. Cavity control servo system feedback control control cavity length
piezo actuator
monolithic elastic hinge
feedback control
transmission intensity
= reference voltage
<0.1 nm resolution

21. Optical cavity and laser
laser specification
wavelength
532 nm
CW power
300 mW
linewidth
<10 kHz (1msec)
LightWave Series 142
diode-pumped solid state laser
CW freq. doubled YAG laser
cavity specification
horizontal wire
(vertical measurement)
vertical wire
(horizontal measurement)
mirror
front
99.1 %
99.8 %
reflectance
end
99.9 %
mirror curvature
20 mm
finesse
620
1700
power gain
660
1300
size (rms)
5.67　± 0.1 μm
14.7 ± 0.2 μm
Rayleigh range
760 μm
5100 μm

22. Laser power modulation
background subtraction
background ~ 10kHz
Laser-ON / Laser-OFF measurement
modulate intra-cavity power (cavity length modulation)
Laser-ON:
Laser-OFF:
113 Hz sinusoidal modulation
30% (time)
85% of power (average)
30% (time)
7.5% of power (average)

23. Detector Compton scattering gamma ray detector time resolution
28.6 MeV (max gamma energy)
23.0 MeV ( 0.2 mrad scattering angle )
gamma ray detector
[70 mm ×70 mm ×300 mm ]
CsI(pure) crystal
2” photo-multiplier
time resolution
PMT signal leading edge
0.56 nsec resolution
(signal energy region)
enough to separate 2.8ns spacing bunches

24. Compton scattering signal
Energy spectrum
signal/background = 4 / 1 (vertical beamsize measurement)
energy window (15MeV – 25MeV)
“counting” method
no event pile-up (10kHz rate / 2MHz ring revolution )
energy gate and leading edge detection
bunch identification by gamma ray signal timing

25. Signal processing single bunch emittance (Mar 2003)
20 beam profiles (multi-bunch) at the same time
bunch ID by hit timing (bunch marker)
laser ON/OFF count rate
single bunch emittance (Mar 2003)

26. Data taking scanning align collimators
beam based alignment for collimators
local orbit bump at laserwire position if needed
scanning
1 round trip for 1 profile
automatic scan
vertical
10sec. for 1 position
move 10 micron (6sec.)
6 min. for 1 scan
error dominated by orbit drift
horizontal
30sec for 1 position
move 50 micron (10sec.)
15 min. for 1scan
error dominated by statistics
vertical
“bad data”

27. Laser waist measurement
longitudinal laser profile
laser has parabolic shape
small waist size ⇔　small Rayleigh length
change x-position and confirm laser profile
laserwire size = 5.67 ±0.1 μm
(laser divergence method)
laserwire size = 5.46 ±0.2 μm
(fitting from focus scan)

28. Additional data beta function at two collision points
dispersion measurement by laserwire itself
change Ring RF
scan beam by laserwire
measure the beam position shift
vertical dispersion = 2.0 mm (almost negligible)
horizontal dispersion = 2.0 mm (negligible)
beta function at two collision points
for vertical measurement βx= 9.81 m, βy= 4.32 m
for horizontal measurement βx= 7.83 m, βy= 4.90 m

29. Beam damping measurement
beamsize measurement as a function of storage time
study detector response after beam injection

30. Recent Results with calculated values on intra-beam scattering and pure inductive impedance
Bunch
Length
Energy
Spread
Horizontal
Emittance
Vertical
Emittance

31. Future plan possibilities How to improve resolution ?
beam size : 5.5 [mm] 　⇔ 　　laser waist size: 5.6 [mm]
close to the resolution limit
possibilities
stronger focusing
fine tuning of cavity length
sensitive to mirror geometries
shorter Rayleigh length
shorter wave length
high quality mirror
high power / stable laser
use higher transverse mode

32. Twin peaks laserwire
use TEM01 resonance mode in the optical cavity as a laserwire
good resolution for small beam size
factor 2~3 resolution improvement
insensitive for beam orbit drift
scan free

33. Higher mode resonances
misaligned laser injection
higher order mode resonate in the cavity
mirror distortion
　　　　↓
transmitted light profiles of each mode
mode degeneration TEM01/10
mirror distortion to split these modes

34. Higher mode test experiment
stable realization of higher order modes
TEM00
TEM01
TEM02

35. Conclusion Ultra-low emittance electron beam is good for you.
Ultra-short bunched beams are good for my future
R&D.
Now we are going to do nano-beam orbit handling with international collaboration. Sub-nano meter and sub-100f second beam will be realized in the future. Beam diagnostics for above beam are necessary. Idea of such diagnostics exists. However, present technologies are not mature. So, we continue R&D with challenging spirit for future linear collider project.

36. Installation of 5 wire-scanners into ATF Linac
Improvement of temperature control of cooling water
Stabilization of Magnet Power Supply
Increase QE of photo-cathode
Vacuum backing (beam scrubbing) is necessary.
Adding trim coils to both end poles of wigglers which will
be finished in next summer shutdown.
Other issues
Stabilization of extraction kicker system
More precise beam orbit control
100 bunches/pulse electron beam generation and acceleration
Test on beam loading

37. Survey IBS in detail and
Longitudinal instability until 3x1010 electrons/bunch.
Multi-bunch instability until 3 trains with 20 bunches.
Especially Fast Ion Instability with vacuum pump turn-off.
Observation of different beam behavior with wiggler
Schedule
First ATF program (from 1997) will be finished until the end of
JFY 2004.
Second ATF program which includes nano-meter orbit handling
and 1st bunch compression until 1psec(rms) has been already
unofficially discussed.