Transcript ppt - KEK

PULSE LASER WIRE
Laser pulse storage in an optical cavity
as a beam monitor & an X-ray source
Kaori Takezawa
Kyoto Univ.
2nd Mini-Workshop on Nano Project at ATF
12th Dec. / 2004
1. OVERVIEW
2. PRINCIPLE
3. OPTICAL CAVITY
4. EXPERIMENTAL
SETUP
5. CONCLUSION
6. FUTURE PLAN
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1.OVERVIEW
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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1.OVERVIEW
714MHz Cavity
Laser Repetition rate :
357MHz
laser pulses
Electron repetition rate :
357MHz
Electron bunches
Scattered
Gamma beam
Phase Scan
Compton Scattering in every 357MHz
As an X-ray source :
An optical cavity store higher peak power and get
higher flux X-ray with pulse CW laser than CW laser.
As Beam monitor :
By scanning the laser pulse’s phase in the cavity and
measuring the Compton signal count rate ; an electron
bunch length profile is obtained.
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2.PRINCIPLE : Storage of laser pulse
Resonance condition :
Perfect resonance : Llaser = L cavity
The relationship with
laser and cavity :
Imperfect Resonance : L laser ～ L cavity
The ext. cavity’s
parameters ;
enhancement factor ,
reflectivity , …. is the
function of Δl and laser
pulse width.
Not resonance : L laser≠ L cavity
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2.PRINCIPLE : Enhancement factor
The reflectivity is bigger at resonance point with Δl ≠0,.this means that
enhancement factor is smaller . And data says laser pulse width.
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2.PRINCIPLE :Count rate& Measurement
Signal flux
+σe2- v-beamwaist
σ 2 = σ 2Laser
beamwaist
Phase
Vertical
position
2
2
σ = σLaser pulse +σ
width
～σ2Laser pulse
width
2
e- bunch
length
2
+σ Laser
Suppose both electron
bunch and laser pulses
have a Gaussian intensity
distribution, The measured
profile is also a Gaussian
shape.
2
+σe- h-beamsize
beamwaist
The electron bunch length is 20 ～ 40 psec (10mm)
> Laser pulse width ( FWHM =7 psec ; 1 mm)
>> Laserwire beamwaist( 120um ), electron’s horizontal
beamsize ( 100um )
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3.OPTICAL CAVITY
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3.OPTICAL CAVITY : The design
• Cavity length : 714 MHz +/- 2 kHz ( from PZT dynamic range )
Cavity length is 210mm. It is easy to adjust cavity length with short cavity.
For cavity’s dynamic range , long PZT is used ( 10um ).
• Mirrors
• The radius of curvature : 250 mm
• The reflectivity : 0.997 +/- 0.001
Finesse is ～ 1000 . But Maximum finesse is ～500 ,when the cavity , the
length is 714MHz , stores laser pulses, which repetition rate is 357MHz. For
enhanced laser pulses in the cavity , Next pulse come after 4times reflection
• Beamwaist > 200 um
It is difficult to make thin laserwires at long cavity length .
ρ= 250mm
R = 0.997
714MHz
Adjustment with PZT
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3.OPTICAL CAVITY : feedback circuit
Transmission
PZT voltage
PI circuit
Mode locked
Laser
A trombone
for a signal
delay
Laser Rep.rate
feedback
357MHz
Ring RF standard
10MHz
Signal
Generator
←
DC
Shoulder feedback
system
( OFF : background)
By a phase
detector, the signal
is synchronized
with Ring 357MHz
Feedback ON/OFF
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4.EXPRIMENTAL SETUP : Layout
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4.EXPERIMENTAL SETUP : Optics
λ/2
Isolator
λ/4
Reflection
Injection mirrors
Transmission
Cavity
Laser head
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5.CONCLUSION : Timing scan
← Compton signal
In timing scan, we
2.8 nsec
Bunch length
detect Compton
signals and the laser
pulse’s phase in cavity
when signals come.
Enhanced laser pulses
2times go and back in
the cavity , and are
scattered 4times
every 2.8 nsec.
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5.CONCLUSION : count rate
σ=laser beamwaist
Calculated maximum count rate is～ 2500 [Hz/mA] .
Actual count rate is ～ 1500 because of imperfectly adjustment
cavity length with shoulder feedback system.
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5.CONCLUSION : VS. RF voltage
Data at 19th Nov. had a sharp peak , but There was no peak at 01st Dec.
( Because of the change Ring tune ? )
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5.CONCLUSION : VS. the beam current
Count
rate
[Hz/mA]
When the number of electron per bunch is bigger ,
The Gauusian shape of scattered photons count
rate change.
(The life time of low current electron beam at ring
is long )
Phase [psec]
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6. FUTURE PLAN
• For high count rate :
We plan the higher finesse cavity (mirror R=0.999) and thin laserwire
with beamwaist 50um. In the plan , the enhancement factor is 10
times as much as current systems.
New feedback system, Tilt locking can adjust cavity length at
resonance peak . We will test those systems in this winter.
• Problems as a bunch length monitor :
In current systems, It takes about 20 seconds for data taking . Data can
be taken at low current electron beam , but at high current beam cannot .
• And now
Next week, we will measure bunch length with pulse laser wire timing
scan and streak camera. If I can, we will test tiltlocking feedback
system.
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Kyoto Univ.
NIRS
KEK
Thanks !
Jaeri
ISSP
And you !!
2nd Mini-Workshop on Nano Project at ATF
12th Dec. / 2004
1. 企画書の目的と概要
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1. 企画書の目的と概要
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4.EXPERIMENTAL SETUP : Data taking
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