In this article, the electron trapping and acceleration in the wake field driven by an ultrarelativistic hollow electron beam is studied. When the hollow driver injects into plasma, there is a doughnut-shaped electron bubble formed because of the existence of a special ‘backflow’ beam in the centre of the electron bubble. At the same time, there is a transverse convergence of the hollow driver, which leads to the weakening of the backflow beam. This results in a local electron density transition at the rear of the bubble. During this process, there is an expansion of the longitudinal electron bubble size, and a bunch of background electrons is trapped by the wake field at the rear of the bubble. The tracks for the trapped electrons show that there are two sources: one is from the bubble sheath and the other is from the unique backflow beam. In the particle-in-cell simulation where the driving beam has initial energy of $1.0$ GeV per particle, the trapped beam can be accelerated to energy of more than $1.5$ GeV per particle and the corresponding transformer ratio is $1.5$ . With the increase of driving beam energy up to $40.0$ GeV, a transformer ratio of $1.4$ still can be achieved. By adjusting the hollow beam density, it is possible to control the trapped beam charge value and beam quality, such as its energy spread and transverse emittance.

中文翻译：

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由演化的空心电子束产生的等离子体尾流场中的电子俘获和加速

在本文中，研究了由超相对论空心电子束驱动的尾流场中的电子俘获和加速。当空心驱动器注入等离子体时，由于电子泡中心存在特殊的“回流”束，会形成一个环形电子泡。同时，空心驱动器存在横向收敛，导致回流光束减弱。这导致气泡后部的局部电子密度转变。在此过程中，纵向电子气泡尺寸扩大，一束背景电子被气泡后部的尾流场俘获。被俘获电子的轨迹显示有两个来源：一个来自气泡鞘，另一个来自独特的回流束。 $1.0$ 每个粒子 GeV，被捕获的光束可以加速到超过 1.5 美元 每个粒子的 GeV 和相应的变压器比为 1.5 美元 . 随着驱动光束能量的增加高达 $40.0$ GeV，变压比 $1.4$ 还是可以实现的。通过调整空心光束密度，可以控制被困光束电荷值和光束质量，例如其能量扩散和横向发射率。