Wakefield and Impedance Studies with Ultra-Relativistic Beams for CLARA and UK FEL

位于达雷斯伯里的电子束加速器被设计用于将电荷为250 pC的非常短的电子束加速到250 MeV的能量。这些长度为飞秒的束流对整个加速器中各种组件（如波纹管、弯曲和其他过渡和障碍物）的过渡所产生的尾场敏感。这些尾流场的傅里叶变换构成了束流阻抗。这一点，以及相应的由超相对论性光束激发的韦克菲尔德场，将用台式测量技术，以及在英国VELA/CERN和欧洲核子研究中心的CALFES上进行的基于光束的测量来测量。复杂的分析技术和一套模拟也将被用来计算韦克菲尔德和束流动力学。这项研究的目的是分析的众多组成部分，在CAXA加速器，从分析模型，在适当的情况下，数值模拟，和台式测量的韦克菲尔德。几种新的分析方法将被用来获得与这些加速器组件相关的尾场的一般行为的理解。这将直接适用于CLARA设施和UK-FEL。这个项目是物理学和工程学的交叉。物理方面涉及研究的基本韦克菲尔德方面的ESTA加速器-和他们的相互作用，通过先进的束流动力学模拟束。工程部分涉及评估与每个部件相关的韦克菲尔德和阻抗，并在适当时提出改进技术。我们期待与欧洲核子研究中心的同事合作，特别是在CALIFES设施。类似的特性已经应用于LHC加速器中的组件-导致阻抗预算，允许升级阶段继续进行。 该项目必然需要射频和束流动力学之间的强耦合-其中组件的束流阻抗将被表征，并通过分析模型和强束流动力学模拟评估对束流的影响。

The CLARA accelerator at Daresbury is designed to accelerate very short bunches of electrons, with a charge of 250 pC, to an energy of 250 MeV. These bunches, femto second in length, are sensitive to wakefields generated by transitions in various components in the overall accelerator -such as bellows, bends, and other transitions and obstacles. The Fourier transform of this wakefields constitute the beam impedance. This, and the corresponding wakefield excited by ultra-relativistic beams, will be measured with bench-top measurement techniques, and with beam-based measurements at VELA/CLARA in the UK and on CALFIFES at CERN. Sophisticated analytical techniques and a suite of simulations will also be employed to characterise both the wakefield and the beam dynamics. The purpose of this research will be to analyse a multitude of components in the CLARA accelerator, characterise the wakefield both from analytical models, where appropriate, numerical simulation, and bench top measurements. Several novel analytical methods will be employed to gain an understanding of the general behaviour of wakefields associated with these accelerator components. This will have direct application to the CLARA facility, and UK-FEL. This project is a crossover between physics and engineering. The physics aspect involves studying the fundamental wakefield aspects of the CLARA accelerator -and their interaction with the beam through advanced beam dynamics simulations. The engineering component is concerned with assessing the wakefield and impedance associated with each component and suggesting amelioration techniques where appropriate. We anticipate collaboration with CERN colleagues on the CALIFES facility in particular. A similar characterisation has been applied to components in the LHC accelerator -resulting in an impedance budget which allowed the upgrade phase to proceed. This project will necessarily entail a strong coupling between rf and beam dynamics -in which the beam impedance of components will be characterised and the implications on the beam assessed with analytical models and intense beam dynamics simulations.