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2008 6/18

Yasuaki Ushio

Hiroshima University

The result of cavity compton experiment

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Contents

• Set up at KEK – ATF

• Procedure of measurement

• Result of the experiment

• Summary

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Set up at KEK-ATF 1

Optical cavity

slit aperture ~0.26mrad

e - e - beam

15.6m

detector

set up

ray

In our set up, the minimum solid angle of gamma

to be detected was determined to this slit aperture 0.26mrad.

This value determined to one of gamma minimum energy.

A gamma energy was from 16MeV to 28MeV.

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Set up at KEK-ATF 2

ray

Pure CsI scintillator

lead shield15mm

UV-pass filter

light guide

PMT

UV-pass filter : Only pass the ultraviolet light.

Pure CsI : The maximum emission wavelength : 315nm Emission decay time : 10-16ns

Emission decay time is enough to be faster than the data taking time and electron frequency.

electron frequency : 2.16MHz ~ 463 ns

data taking time : 100ns

300mm

slit aperture ~0.26mrad

e e - - detector

set up

ray

beam

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Set up at KEK-ATF 3

accuracy ~ 0.8m

electron beam

Horizontal

Vertical

Optical cavity

Cavity position is moved

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The appearance of light resonance signal

Reflected light

Transmitted light

In this time, the optical cavity was resonated state

Transmitted light

Mirror reflectivity : 99.6%

Mode locked laser

(Photo diode)

PD

time (ms)Continued to change the length of the external cavity.

1ms

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DAQ Schematic

Continued to change the length of the external cavity.

Only picked up the data when the cavity was resonated.

2.16MHz

- e

cavity

Could pass Comparator

Gate was opened

for 100ns.

T = 463ns

PD

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Procedure of measurement 1

① Vertical scan

Scanning to the laser vertical position and find the best position to observe gamma

Vertical scan

② Horizontal scan

Vertical was fixed to the best position.

Scanning to the Horizontal.

Moved accuracy ~ 0.8m

movable table

movable table

See from upper direction.At horizontal, cavity was leaned at 12 degree

Z

e-

e-

When Vertical scan,Moved the cavity to Z direction

Z

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Procedure of measurement 2

We found the best collision point

③ Timing scan

Vertical and Horizontal were fixed to the best position.

And turned on the switch of phase locked loop .

After that scanning phase.

Timing scan

- e beam

420mm

T=2.8ns

pulsed laser

beame -

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Gamma Energy distribution 1

In calculation, the peak energy of a gamma is about 28MeV.In our set up, the acceptance of detector was 0.26mrad.

One of gamma had 16~28 MeV energy.

Our set up detected a lot of gamma at one time.

So we estimated the number of gamma at the place of detector.

detected in experiment

15.6m

cavity

slitaperture 0.26mrad

ray

detector

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Gamma Energy distribution 2

This graph shows the appearance of gamma energy distribution.

one of gamma had 16~28 MeV energy.

1 gamma

2 gamma

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The number of gamma

1 bunch : experiment ~3.3 simulated by CAIN ~ 4.5

20 bunches : experiment ~3.1 simulated by CAIN 　 ~ 20

In the case of 1 bunch, the number of gamma seems to consist comparing our experiment data with estimate by CAIN.

However, the data of 20bunches were inconsistent.The reason of this,there was a possibility that not every electron bunches were collided.

We estimated the number of gamma to use a simulation software “CAIN”.

bunch distance : 2.8 ns

date bunch the number of electron transmitted power stack power estimate γ1/ pulse (included in one train) W W

2008/ 4/ 22 20 2.6E+10 (in 20 bunches) 1.55 388 3.12008/ 5/ 27 1 7.2E+9 (in 1 bunch) 1.09 272 3.27

Mirror reflectivity : 99.6%1 - 0.996

transmitted powerstack power =

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Summary

・ The data of 1 bunch appears to be consistent with simulation data by CAIN.

・ We observed the number of gamma about 3.3 per collision.

・ The data of multi bunch mode was inconsistent.There was a possibility that not every electron bunches were collided.

・ The optical cavity length will be fixed at a condition of synchronization with electron cycle. And will be detected to the largest number of gamma in our set up.

Next Plan

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15

16

Set up at KEK-ATF

1-R

Mode lock laser

Electron beamCSIγray

e beam

PD

Transmitted light was detected

16~28MeV

We could observehow stored it was.

420mm

Collision angle 12 degree

Mirror curvature : 210.5mm

λ:1064nm Output : 28nJ/pulse=10WDistance of per pulse : 2.8ns = electron bunch distance(Internal cavity length : 420mm)Pulse length : 7ps

Rate of reflection : 99.6%

πRF =

Finess By calculationF = 780σ = 30 μm

Mode lock laser

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The number of gamma

When we estimate the laser power in the cavity, we should use the data from transmitted light.

Since the stack power estimate by input was considered inaccuracy.

1 bunch : γ~3.3 simulated by cain γ~ 4.5

date Finesse electron bunch transmitted power incident power reflected power input power γ γ estimate by cain1/ pulse W W W W by transmit by input

2008/ 4/ 22 486 2.6E+10 20 1.55 5.3 2.55 2.75 388 425 3.1 20 (388W)2008/ 5/ 27 1010 7.2E+09 1 1.09 6 3 3 272 964 3.27 4.5 (272W)

stack power estimate[W]

20 bunch : γ~3.1 simulated by cain 　 γ~ 20

We estimated the number of gamma to use a simulation software “cain”.

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Set up at KEK-ATF 2

ray

Pure CsI scintillator

lead shield15mm

UV-pass filter

light guide

PMT

UV-pass filter : Only pass the rapid time reaction element.Pure CsI : The maximum emission wavelength is about 305nm.

The rapid time reaction element was enough to be faster than data taking time and electron frequency.

electron frequency : 2.16MHz ~ 463 ns

data taking time : 100ns

300mm

slit aperture ~0.26mrad

e e - - detector

set up

ray

beam

peak wavelength (nm) decay time (ns)2(35%)20(65%)

Pure CsI (slow time reaction element) 450 100 - 4000

305Pure CsI (rapid time reaction element)

レーザーと光学系

共振器長 420mm

圧電素子でミラーの光軸方向の位置を変化

衝突角 12 度

透過光強度を検出→ 共振のモニター

反射率99.6%

光学セットアップ