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Compton Gamma-ray Generation
Experiment by Using an Optical
Cavity in ATF
POSIPOL 2007 Workshop at LAL
Hirotaka Shimizu
Hiroshima University
Topics
• Introduction
• R&D Report in ATF
• Future Plan in ATF
Introduction －Cavity-Compton Collaboration－
Q.1) Why does R&D for Polarized Positron
be needed ?
Introduction
1 / 10 !
e- : 80% Polarization
e+ : 60% Polarization
with GRACE System Developed by Computational Physics Group in KEK
Introduction －Cavity-Compton Collaboration－
Q1) Why does R&D for Polarized Positron
be needed ?
Ans.) For forthcoming ILC era, Polarized
Positron will play a very important roll.
N
New Physics Search
Background Suppression
Introduction －Cavity-Compton Collaboration－
Q.2) Then, how to start R&D ?
・ Is there any good Equipments ?
・ Also, any good Collaborators ?
・ And good enough Advantages ?
The Clue is Accelerator Test Facility (ATF)
～ 54 m
Beam Energy
→ 1.28GeV
～ 30 m
Beam Size
→ 100μm×10μm
Emittance →
1.0x10^-9 rad.m
1.0x10^-11 rad.m
(Ultra
Low !!)
and in ATF, we meet
• Laser-Wire Collaborations
advanced electron beam monitor system
with laser & stacking cavity.
• LUCX Collaborations
(Laser Undulator Compact X-ray source)
creating X-ray with Compton backward
scattering scheme at small lineac in ATF.
→ Highly Accumulated Technique about Laser and Stacking Cavity
Introduction －Cavity-Compton Collaboration－
Q.2) Then, how to start R&D ?
・ Is there any good Equipments ?
・ Also, any good Collaborators ?
・ And good enough Advantages ?
Ans.) We’ve started Cavity-Compton
Collaboration for R&D study of Polarized
Positron in ATF.
R&D Report in ATF
• Basic Concepts (Our Strategy #1)
◇ Simple Structure Cavity (2 mirrors)
◇ Enhancement Factor ～ 1000
→ Quick Construct
& Have an experiment in ATF DR
R&D Report in ATF
Laser Section
Type
Power
Frequency
Pulse Width
Cavity Section
Length
Mirror Reflection Rate
Beam Waist
Crossing Angle
YAG-VAN (1064nm)
10 W
357 MHz
10 ps
420 mm
99.7 %
60 μm ( in 2σ)
12 degree
R&D Report in ATF
• Experiment (Our Strategy #2)
◇Using CW laser (training laser)
before going to pulse laser use.
Training Cavity with CW laser
Training Cavity with Pulse Laser
Real Cavity with CW laser
Real Cavity with Pulse laser
Set Up for Training Configuration
obtaining transmission
external cavity
Laser
photo diode
oscilloscope
high-voltage amp.
function generator
TEM00 mode signal
Voltage
time
modulation with chopping wave
Guoy Phase factor
external cavity
Free Spectral Range (FSR)
photo diode
Full Width Half Maximum
high-voltage amp.
function generator
Typical examples of observations
• With training configuration, 800～900 finesse
can be reached constantly.
• Also, observed beam waist achieved inside the
cavity is stably about 60μm.
for Feed-Back,
0 [V]
0 [V]
DC off-set (< 0)
0 [V]
(feed-back point)
high-voltage amp.
P & I circuit
For the first step, using usual analog PID-module (function “D” is turned off).
Transition Light
Error Signal
Piezo Modulation
Reflected Light
● Those results are
obtained with each time
constant (parenthetic).
Turn to Pulse Laser Set-Up
first try with pulse laser
• Have not reached to the best matching condition yet.
→ achieved finesse ～ 200
→ beam waist size ～ 67μm
• Need more practice to erase higher mode peaks, and to get more
high finesse value.
•
Feed-Back study results
Transmission Light
Integration (1ms)
Error Signal
Integration (10ms)
Reflected Light
Equipments
－ status report －
• Real Cavity has delivered.
• Recently, vacuum chamber has also come.
• After this tour, mover table will arrive at
KEK.
Port for CCG
ATF e-Beam
Port for ion pump
Laser
Terminal for piezo
End cap
Inner pipe for electron
Trunc
Small hales on the pipe near IP
Piezo housing
e-Beam
12deg.
Laser
Mirror housing
Further Plan in ATF
－ as a summary of this talk －
• Laser stacking studies should be
continued.
• Parallel with those studies, preparations
for the installation also have to be started.
• Indeed there’s huge time delay, however,
we’ll try to install our equipments during
this summer shutdown into the DR.
Merci !