Beam Dynamics of CBETA and its potential applications to the UK-XFEL

EMMA(具有多种应用的电子机)是世界上第一台无比例FFAG，在达累斯伯里实验室建造和运行。Emma成功地演示了一种新型的加速以及一种新型的光束传输[1]。艾玛使用爱丽丝(联合实验中的加速器和激光)作为注射器。爱丽丝是一名能量恢复直线加速器(ERL)加速器。美国康奈尔大学与布鲁克海文国家实验室(BNL)合作的一个新项目目前正在进行[2]。该项目将在Emma上演示的无比例FFAG概念与能量回收的想法结合到一个称为CBETA(康奈尔和布鲁克海文ERL测试加速器)的加速器中。CBETA是电子-离子对撞机(EIC)电子传输部分的原型，它使用再循环将电子束能量增加到永久、Halbach类型、高接受度、四极和复合功能磁体中的四倍。由于再循环使用了与EMMA相同的无比例FFAG形式的传输，所有的能量轨迹都适合同一弧线。这种新颖的再循环风格为下一阶段带来了一些非常有趣的选择，像CBETA这样的加速器可能具有这种选择。特别是，如果这四种不同的能量可以很容易地分离并保持束团质量，那么就应该有可能运行四种不同的能量，从而输出波长，自由电子激光(FEL)。此外，四种不同的自由电子激光将完全同步，从而促进生物样品的泵浦-探测器实验等。这可能需要添加元素，如六极或更高阶磁铁，目的是改善光束质量，以确保束流的激光。博士生将探索各种可能性，以改善输出束团，并形成更广泛的合作的中心部分，就可能的CBETA升级而言，如下所述*。该学生还将在CBETA第一阶段的试运行中发挥积极作用。

EMMA (Electron Machine with Many Applications) was the world's first non-scaling FFAG and was built and operated at Daresbury Laboratory. EMMA successfully demonstrated a new type of acceleration as well as a new type of beam transport [1]. EMMA used the ALICE (Accelerators and Lasers In Combined Experiments) as an injector. ALICE was an energy recovery linac (ERL) accelerator.A new project is currently underway at Cornell University in the US, in collaboration with Brookhaven National Laboratory (BNL) [2]. This project combines the non-scaling FFAG concept demonstrated on EMMA together with the idea of energy recovery into one accelerator called CBETA (Cornell and Brookhaven ERL Test Accelerator). CBETA is a prototype for the electron transport part of an electron-ion collider (EIC) and it uses recirculation to increase the electron beam energy by a factor of four in permanent, Halbach-type, high acceptance, quadrupoles and combined function magnets. Because the recirculation uses the same non-scaling FFAG style transport that was used on EMMA, all the energy trajectory fit in the same arc.This novel style of recirculation leads to some extremely interesting options for the next phases that an accelerator like CBETA could have. In particular, if the four different energies can easily be separated and the bunch quality preserved, then it should be possible to run four different energies, and hence output wavelengths, free electron lasers (FELs). Furthermore, the four different FELs would be perfectly synchronised thus facilitating pump-probe experiments with biological samples etc. This may require the addition of elements such as sextupoles or higher order magnets with the purpose of ameliorating the beam quality so as to ensure lasing of the bunch.The PhD student would be expected to explore the various possibilities for improving the output bunch as well as forming a central part, as far as a possible CBETA upgrade is concerned, of the wider collaboration outlined below*. The student would also be expected to have an active role in the commissioning of the first phase of CBETA.