Specification of the laser system and signal detection, chicane issues J'Urakawa for G'Blair

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Specification of the laser system and signal
detection, chicane issues J.Urakawa for G.Blair
This is my private opinion including recent
results and future expectation. The opinion of
G.Blair was given in ATF report Vol.1.

• 1. Experience of Laser Wire in Damping Ring,
• 2. Pulsed laser wire development,
• 3. Possibility of Laser Interferometer with an
  optical cavity,
• 4. Plan of test experiment
• 5. Future plan
• 6. Consideration for laser wire monitor
• 7. My conclusion for Grahame

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CW Laser wire beam size monitor in DR
1. Experience of Laser Wire in Damping Ring
14.7µm laser wire for X scan 5.7µm for Y
scan (whole scan 15min for X, 6min for Y)
300mW 532nm Solid-state Laser fed into optical
cavity
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Compton scattering signal

• Energy spectrum

signal/background 4 / 1 (vertical beam size
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
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Example of profile measurement
2.0mm dispersion is still large considering
future experiments.
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2. Pulsed laser wire development

• Experimental results(Pulse Laser Storage)

Laser
Mode Lock Passive SESAM Frequency 357MHz Cav
ity length 0.42 m Pulse width 7.3 p
sec (FWHM) Wave Length 1064 nm Power 6W
SESAM SEmi-conductor Saturable Absorber Mirrors
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Ext. Cavity
Cavity Super Invar Cavity length 0.42
m Mirrors Reflectivity 99.7,
99.9 Curvature 250 mm (?0 180µm)
super invar
62f
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Plused Laser and Electron Beam Collision to
measure bunch length
Pulse Laser Wire (Storage laser pulses in
optical cavity ) The systems for New X-ray
source New bunch length monitor at a storage
ring.
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Pulsed Laser Wire at EXT

• University of Oxford
• Royal Holloway University London
• University College London
• SLAC
• KEK
• Vertical scanning Laser Wire
• Installation in September 2005
• Full system commissioning by December 2005.
• ATF2 beam size monitor

Beam

• Measure the electron beam profile with 1 ?m
  laser(waist).
• Tiny electron beam is preferable.
• A few mm in s.

G. Blair
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Beam Extraction Study
Extract the beam with ILC like bunch spacing

• Performance of the double kicker system has been
  confirmed by KEK kickers.
• Install the SLAC kickers modified for the double
  kicker system with 300ns (flat top) pulse in
  September 2005.

Store 3 bunches in DR by 3 injections Injection
kicker 60ns(rise/fall/flat-top)
Extract beams in a kicker pulse Extraction kicker
60ns(rise), 300ns (flat-top)
ILC like beam bunches for EXT line and ATF2
150ns 150ns
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3. Possibility of Laser Interferometer in an
Optical Cavity
Short laser pulse can be generated by many
longitudinal waves which are completely
mode-locked. 7psec pulse width requires 200
longitudinal modes in the case of 714MHz
repetition rate.
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Check by Mathematica in my laptop computer
Cavity Length 420mm, Center of the Cavity is
z0. Two 7psec laser pulses are moving upward and
downward from high reflective Mirrors at t0.
710.000762psec later
705.000762psec later
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Interference
700.00076psec later
700.002psec later
700.0033psec later
700.003psec later

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4. Plan of Test Experiment
We ordered 741MHz mode-lock laser. Specification
of the 714MHz mode- lock laser. It will come on
March. 800mW (20W), 7psec pulse width (FWHM),
0.4psec(rms) timing jitter First step
Confirmation of Interference (2006 ??, maybe
2007) Second step Movement of the Interference
by phase shift or mover table (2006). Table will
be completed soon. Third step Installation into
ATF Damping ring in this summer or Extraction
Line in 2007 summer
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2000
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200nm 300nm 400nm 500nm
The calculated results of number of photons
(a) Unit of Vertical axis normalized by 150
counts. (b) It normalized by 90 counts. Electron
vertical beam sizes are 30 nm, 50 nm, 100 nm and
200 nm with the horizontal beam size of 3 mm.
More counts rate is necessary, maybe 10
times more.
1064nm
532nm
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4. Plan of Test Experiment

• We ordered passive mode-lock laser with 714MHz
  rep. rate with two special options.
• We started the manufacture of 0.42 m length
  optical cavity with precise feedback system.
• We will start the measurement of the interference
  from April in 2006 at KEK.
• We will install this device during next summer
  shutdown for g generation experiment. (This is
  not
• interference experiment.)

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5. Future plan

• We will design the chamber which includes
  vertical 42cm optical cavity and is attached with
  upstream cavity BPM and downstream cavity BPM.
  Two BPMs can measure the beam orbit within the
  accuracy of a few nano-meter.
• We will change the laser wavelength from 1064nm
  to 532nm(Green).
• This is a backup system for Shintake monitor.

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6.Consideration for laser wire monitor
EXT Diagnostic Section (optimal 2.2)
SQ
SQ
SQ
SQ
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
2.0
1.3
1.3
1.3
1.3
WS
WS
WS
WS
WS
x y
90 90
180 90
90 90
33 57
57 33
33 57
57 33
59.2 8.3
108.0 4.5
59.2 8.3
108.0 4.5
59.2 8.3
s (µm)
7 lt sx/sy lt 24
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• Optimal 2.4 remove chicane reduce BH2X.1
  lengthen skew/emit section
• minimize changes to existing EXT magnets and
  power supplies
• optimize vertical spot sizes at wire scanners
  (big enough for 10 µm tungsten or carbon filament
  wires, small enough to generate reasonable gamma
  flux from laser wire 5 µm?)
• Laser wire detectors between FF B5 and QD6
• IP moves 0.5 m west and 10.2 m north

7.6 m wall to dump face (13.6 m wall to IP)
Assembly Hall
EXT optics for this option is still under
construction more later!
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1.8m
QD6
B5 0.8m 2.76kGs
140mm
49mm
g
51 mrad
0.35m
0.2m
If laser wire photons detected after B5, in front
of QF5, special BPM is needed for QD6
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B5
ßx,y 4,0.1 mm
QD6
?------------? 30m
Ring BPM is possible or not.
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ATF Damping Ring BPM
Electronics single pass detection for 96 BPMs,
base line clip charge ADC,
min. resolution 2µm
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7. My Conclusion for Grahame ?

• We do not need the chicane.
• Good collimation is necessary. 10mm diameter, 1 -
  5m long collimation is preferable? Check!
• Good vacuum level is necessary. (like the ring.)
• Ring Button BPM is possible? Check!
• Present Laser Specification 532nm, 300mJ/pulse,
  200psec(FWHM), 10Hz operation, mode-locked laser
  by 357MHz.
• We can expect enough signals, background is
  negligible? Check!
• Thank you for good work of Mark and Andrei!