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 ?

1 / 10 ! with GRACE System Developed by Computational Physics Group in KEKComputational Physics Group Introduction

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 ～ 30 m Beam Energy → 1.28GeV 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 TypeYAG-VAN (1064nm) Power10 W Frequency357 MHz Pulse Width10 ps Cavity Section Length420 mm Mirror Reflection Rate99.7 % Beam Waist60 μm ( in 2σ) Crossing Angle12 degree

Experiment (Our Strategy #2) ◇ Using CW laser (training laser) before going to pulse laser use. R&D Report in ATF 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

function generator high-voltage amp. external cavity photo diodeoscilloscope Laser Voltage time obtaining transmission modulation with chopping wave TEM 00 mode signal

function generator high-voltage amp. external cavity photo diode Free Spectral Range (FSR) Guoy Phase factor Full Width Half Maximum

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.

0 [V] DC off-set (< 0) 0 [V] high-voltage amp. P & I circuit 0 [V] (feed-back point) for Feed-Back, 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 Error Signal Reflected Light Integration (1ms) Integration (10ms)

Equipments － status report － Real Cavity has delivered. Recently, vacuum chamber has also come. After this tour, mover table will arrive at KEK.

ATF e-Beam Laser Port for ion pump Terminal for piezo Port for CCG

Trunc End cap Inner pipe for electron

the Small hales on the pipe near IP

Laser e-Beam Mirror housing Piezo housing 12deg.

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 !