Positron Source
 
  • Introduction

In order to get polarized positrons, polarized gamma rays will be used to generate positrons. There are two schemes for the generation of gamma rays. One is the Undulator Based Positron Source and the other one is Compton Back-Scattering Based Positron Source. Compton back-scattering based scheme is an advanced alternative because it requires only a few GeV electron beams to produce high energy gamma for the positron generation. It is more than 100 GeV in the case of the Undulator Source. Furthermore, the Compton Source does not make any inter-system dependency between the electron and positron arms in ILC and makes the total system availability better. In addition to the system engineering perception, the positron source based on the Compton back-scattering is more compact and can be demonstrated prior to the construction of the real ILC in equivalent conditions (beam energy, positron intensity, etc). It is practically impossible in the case of the Undulator source, yet it dramatically relieves the system risk. We have participated in the laser Compton back-scattering based positron source experiment operated on the ATF of KEK since 2006.

 
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Figure1: Experimental Scheme

 
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Figure2: Laser and electron beam collision design
 
  • Status and Plan

Now, we have finished the design of the Optical Cavity, Vacuum Chamber, Moveable Table and also we have done some important tests about the parameters of high power Laser source. We also did some simulation of the laser beam transport in the Cavity by GLAD and got the gamma photons distribution through the calculation of CAIN.

 
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Figure3: Photon Energy Spectrum at 4.5m downstream

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Figure4: Distribution of photon at 4.5m downstream
 

Next step, we will use the test Cavity to realize Laser beam stacking in the test Cavity and then realize high circularly-polarized laser stacking in the Cavity and measure the polarization. All the experiment system will be installed to ATF in 2007, after that, we can carry out the collision between electron beam and laser beam and do some interrelated experiment. we will also do more detailed simulation of the laser beam by GLAD and about Compton process by CAIN.

 

X.P. Li , IHEP