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

EMMA（ElectronMachinewithManyApplications）是世界上第一台无结垢的FFAG，在达雷斯伯里实验室建造和运行。EMMA成功地证明了一种新型的加速以及一种新型的束流传输[1]。EMMA使用ALICE（加速器和激光组合实验）作为注入器。ALICE是一种能量回收直线加速器（ERL），目前美国康奈尔大学正在与布鲁克海文国家实验室（BNL）合作进行一个新项目[2]。该项目将EMMA上展示的非缩放FFAG概念与能量回收的想法结合到一个名为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型，高接受度，四极和组合功能磁体的四倍。由于再循环使用了与EMMA相同的非标度FFAG类型的传输，所有的能量轨迹都符合同一弧线。这种新颖的再循环类型为CBETA这样的加速器的下一阶段带来了一些非常有趣的选择。特别是，如果四种不同的能量可以很容易地分离，并保持聚束质量，那么应该有可能运行四种不同的能量，因此输出波长，自由电子激光器（FEL）。此外，四个不同的自由电子激光器将完美地同步，从而促进生物样品等的泵浦探测实验。这可能需要添加元件，如六极或更高阶的磁铁，以改善光束质量，以确保聚束的激光。博士生将被期望探索各种可能性，以改善输出聚束以及形成一个中心部分，就CBETA可能的升级而言，以下概述的更广泛的合作 *。学生也将有望在CBETA第一阶段的调试中发挥积极作用。

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.