Generation of high intensity, multi-bunch polarized positron beams

为了获得高亮度的激光-电子相互作用，我们构建了一个康普顿腔，在其中激光被强聚焦并与电子正面碰撞。2000年10月，我们在CO_2激光与60 MeV电子的碰撞中，获得了背散射x射线的最高峰值强度，7x10^8个光子/秒。我们还开发了限制在等离子体通道内的激光束发生康普顿散射的等离子体通道。因此，相互作用的长度被拉长，导致背向散射的x射线增加。我们成功地制造了长2 cm、半径300 μm的低密度等离子体通道（10^<17>/cm^3）。我们一直在通过康普顿散射和对生成过程进行极化正电子产生的系统研究。用532 nm激光对1.28 GeV电子进行康普顿散射，产生了2x10^5/脉冲的伽玛射线。我们还进行了JLC极化正电子束的概念设计，该设计需要强度为10^<10> e^+ /脉冲的高强度正电子束和复杂的多束结构，即95个脉冲，时间间隔为2.8 ns，重复150 Hz。在5.8 GeV强度为5 × 10^<10> /束的电子束和50段CO_2激光器的作用下，可以产生3x1^<10> /束的正电子。

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.