Generation of high intensity, multi-bunch polarized positron beams

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Studies at BNLIn order to attain laser-electon interaction with high luminosity, we constructed a Compton chamber in which laser is strongly focused and makes head-on collisions with electron. In October, 2000, we achieved the highest peak intensity of back scattered X-rays, 7x10^8 photons/sec in the collision of CO_2 laser with 60 MeV electrons. We have also developed plasma channel in which Compton scattering takes place for the laser beam confined in the channel. Thus the interaction length is elongated, resulting in the increase of the back scattered X-rays. We have successfully fablicated the plasma channel of 2 cm in length and 300 μm in radius having low density(10^<17>/cm^3).Studies at KEKWe have been pursuing systematic studies on polarized positron productions through Compton scattering and pair creation processes. Gamma-rays of 2x10^5/pulse was created in Compton scattering of a 532 nm laser light off the 1.28 GeV electron. We also have made the conceptual design of the polarized positron beam for JLC which requires highly intensive positron beams with the intensity of 10^<10> e^+ /pulse and a complicated multibunch structure, i.e. 95 pulses with the time interval of 2.8 ns repeating 150 Hz. It is found that positrons 3x1^<10> /pulse can be generated using the electron beams of 5.8 GeV with the intensity of 5x10^<10> /bunch and 50 peices of CO_2 lasers.