Owing to their large accelerating gradients, plasma-based accelerators have attracted considerable interest as potential drivers for future, compact electron–positron colliders. Despite great progress achieved in plasma-based electron acceleration, positron acceleration still remains a challenging task, with an efficient positron source being the prerequisite for such acceleration. Here a concept for a compact, two-stage plasma-based positron source is discussed. In the first stage the positrons are created by a multi GeV electron beam produced by a laser-plasma accelerator interacting with a solid density foil. In the second stage the positrons are captured and accelerated in a plasma wave driven by either an electron beam or a laser pulse. Three potential configurations of such a source are considered: (i) a single electron beam is used for both the creation of positrons in the foil and for driving the wakefield in the second stage; (ii) a train of two electron beams is used: the positrons produced by the trailing beam in the foil are captured and accelerated in the second stage by the plasma wave generated by the leading beam; and (iii) a single electron beam is used to produce positrons in the foil and an independent laser pulse is coupled to the second stage to drive the plasma wave. These three configurations show different degrees of effectiveness with positron capture efficiency, varying from less than a percent to almost half of all produced positrons.
由于其加速梯度大，等离子体加速器作为未来紧凑型正负电子对撞机的潜在驱动源而备受关注。尽管等离子体电子加速已取得重大进展，但正电子加速仍是一项挑战，而高效的正电子源是实现此类加速的前提。本文讨论了一种紧凑型两级等离子体正电子源的概念。在第一级中，正电子由激光等离子体加速器产生的高能多GeV电子束与固体密度靶相互作用而产生。在第二级中，正电子被捕获并加速，其加速由电子束或激光脉冲驱动的等离子体尾场完成。考虑了该源的三种可能配置：（i）单束电子束既用于在靶中产生正电子，又用于驱动第二级中的尾场；（ii）使用两束电子束：尾束在靶中产生的正电子被捕获，并在第二级中由前束产生的等离子体尾场加速；（iii）单束电子束用于在靶中产生正电子，而独立的激光脉冲耦合到第二级以驱动尾场。这三种配置在正电子捕获效率上表现出不同程度的有效性，捕获效率从不到百分之一到几乎所有产生的正电子不等。