【摘 要】
：
正电子作为电子的反粒子,在材料科学、核物理与粒子物理研究、实验室天体物理、医学成像等方面有着广泛的应用前景.为了获取正电子,一个传统的方法是通过放射性核素23Na
【机 构】
：
国防科技大学理学院,长沙,410073;空军预警学院,武汉,430019国防科技大学理学院,长沙,410073;上海交通大学IFSA协同创新中心,上海,200240;中国工程物理研究院激光聚变研究中心
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正电子作为电子的反粒子,在材料科学、核物理与粒子物理研究、实验室天体物理、医学成像等方面有着广泛的应用前景.为了获取正电子,一个传统的方法是通过放射性核素23Na的β+衰变.但是这样得到的正电子产额少、能量低,不能满足高密度、高能量密度相关的研究需要.比如,在研究正电子素的玻色-爱因斯坦凝聚时,正电子的密度需要达到10 8cm-3以上.随着激光技术的快速发展,激光的强度越来越高,脉宽越来越短.如果拍瓦级激光得到很好的聚焦,激光的功率密度将达到1024 W/cm2.激光驱动靶产生正电子的方式有三种,即：Trident过程,Bethe-Heilter(BH)过程,Breit-Wheeler(BW)过程,产生的正电子具有高产额(＞1010)、低发散角(＜1rad)、高能量(＞1MeV)、以及超短脉宽(fS)等特点.通过二维粒子模拟程序EPOCH,我们研究了超强激光与稀薄铝等离子体靶相互作用产生高能量密度电子束的过程.考虑BW过程,当激光峰值功率密度为4×1023 W/cm2时,铝等离子体中正电子的产额为5.35×1015,通过在靶后表面开设锥孔,正电子束的发散角可控制在20°.如果进一步提高激光峰值功率密度(4×1023W/cm2),正电子的产额可以增加到3.75×1016,发散角减小到14°.正电子的密度从1.04×1021cm-3提高到4.65×1021cm-3.通过与没有锥孔的平板靶对比,模拟结果表明,锥孔可以有效提高产生正电子束的准直性.
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