/18 Yasuaki Ushio Hiroshima University The result of cavity compton experiment

2 Contents Set up at KEK – ATF Procedure of measurement Result of the experiment Summary

3 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.

4 Set up at KEK-ATF 2  ray Pure CsI scintillator lead shield  15mm 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 nsdata taking time : 100ns 300mm slit aperture ~0.26mrad ee --   detector set up   ray beam

5 Set up at KEK-ATF 3 accuracy ~ 0.8  m electron beam Horizontal Vertical Optical cavity Cavity position is moved

6 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

7 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

8 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 ~ 0.8  m 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

9 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 beam e -

10 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 slit aperture 0.26mrad  ray detector

11 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

12 The number of gamma 1 bunch : experiment  ~3.3 simulated by CAIN   ~ 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 Mirror reflectivity : 99.6% transmitted power stack power=

13 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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16 Set up at KEK-ATF 1-R Mode lock laser Electron beamCSI γray e beam PD Transmitted light was detected 16~28MeV We could observe how stored it was. 420mm Collision angle 12 degree Mirror curvature : 210.5mm λ:1064nm Output : 28nJ/pulse=10W Distance of per pulse : 2.8ns = electron bunch distance (Internal cavity length : 420mm) Pulse length : 7ps Rate of reflection : 99.6% πR F = Finess By calculation F = 780 σ= 30 μm Mode lock laser

17 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~ bunch : γ~3.1 simulated by cain γ ~ 20 We estimated the number of gamma to use a simulation software “cain”.

18 Set up at KEK-ATF 2  ray Pure CsI scintillator lead shield  15mm 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 nsdata taking time : 100ns 300mm slit aperture ~0.26mrad ee --   detector set up   ray beam

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%

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