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Development of a multi-pulse laser wakefield electron accelerator operating at kHz rep-rate

开发以 kHz 重复频率运行的多脉冲激光尾场电子加速器

基本信息

批准号：
1947809
负责人：
金额：
--
依托单位：
University of Oxford
依托单位国家：
英国
项目类别：
Studentship
财政年份：
2017
资助国家：
英国
起止时间：
2017 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=studentship-1947809
关键词：
Development multi pulse laser wakefield

项目摘要

Summary: Laser-driven plasma accelerators can already accelerate electrons to GeV-scale energies in accelerator stages only a few centimetres long. However, the driving lasers used to date can only operate at best at a few pulses per second, and have very low wall-plug efficiencies.The laser-plasma accelerator group at Oxford has pioneered a novel approach for overcoming these limitations: the multi-pulse laser wakefield accelerator (MP-LWFA). In this approach the plasma wakefield is driven by a train of low energy laser pulses. If these pulses are spaced by the plasma period then the wakefields driven by the pulses add coherently, yielding a plasma wave which grows towards the back of the pulse train.The Oxford team recently demonstrated this approach for the first time in experiments performed at the Rutherford Appleton Laboratory (RAL). In that work it was shown that plasma wakefields could indeed be resonantly excited by a train of laser pulses, confirming this validity of this approach.However, to date electrons have not been accelerated by this method since the wakefields driven by MP-LWFA are linear, and as such do not self-trap electrons from the background plasma. The aim of this project is to develop techniques for controlling the injection of electrons into the quasi-linear wakefields driven by a MP-LWFA.Two approaches will be studied. In the first, the use of additional laser pulses to ionize a dopant species will be explored. If a short laser pulse (the "injection" pulse) is focused in the wake driven by the pulse train, then electrons ionized by the second laser pulse can be trapped into the wakefield, and then accelerated. The second approach to be explored will be down-ramp injection. In this method the density of the plasma decreases rapidly with longitudinal position; this slows the wakefield as it moves down the ramp, making it easier for electrons to be trapped, and then accelerated.These injection techniques will be studied through numerical simulations with particle-in-cell (PIC) codes, and compared to the results of experiments performed in Oxford, RAL, and other laser facilities.If successful this work will open the route to a new generation of very compact plasma accelerators operating at multi-kilohertz pulse repetition rates. These would immediately find applications in driving very compact X-ray sources, with widespread utility in ultrafast science, technology, and medicine.

摘要：激光驱动的等离子体加速器已经可以在只有几厘米长的加速器级中将电子加速到GeV级能量。然而，目前使用的驱动激光器只能以每秒几个脉冲的速度工作，并且具有非常低的壁插效率。牛津大学的激光等离子体加速器小组开创了一种克服这些限制的新方法：多脉冲激光韦克菲尔德加速器（MP-LWFA）。在这种方法中，等离子体韦克菲尔德是由一列低能激光脉冲驱动的。如果这些脉冲被等离子体周期间隔开，那么由脉冲驱动的尾场相干地增加，产生朝向脉冲串后面增长的等离子体波。牛津大学的团队最近在卢瑟福阿普尔顿实验室（RAL）进行的实验中首次展示了这种方法。在这项工作中，它表明，等离子体尾场确实可以共振激发一列激光脉冲，证实了这种方法的有效性。然而，迄今为止，电子还没有被这种方法加速，因为尾场驱动的MP-LWFA是线性的，因此不自陷电子从背景等离子体。本计画的目的是发展控制电子注入MP-LWFA驱动的准线性尾场的技术。在第一个，使用额外的激光脉冲，以消除掺杂剂物种将被探索。如果短激光脉冲（“注入”脉冲）聚焦在脉冲串驱动的尾流中，那么被第二激光脉冲电离的电子可以被捕获到韦克菲尔德，然后被加速。第二种方法将被探讨下坡注入。在这种方法中，等离子体的密度随纵向位置迅速减小;这减慢了韦克菲尔德沿斜坡向下移动的速度，使得电子更容易被捕获，然后加速。这些注入技术将通过粒子单元（PIC）代码的数值模拟来研究，并与在牛津大学，RAL，如果这项工作取得成功，将开辟新一代非常紧凑的等离子体加速器的路线，以几千赫兹的脉冲重复率运行。这些将立即在驱动非常紧凑的X射线源中找到应用，并在超快科学，技术和医学中广泛应用。