Provision for Timing Mode Users at Multi-Bend Achromat Synchrotron Light Sources

同步加速器光源的电子储存环的设计正在逐步改变。最新的结构由带有多个弯曲磁铁的磁体单元组成，这些磁体将电子束发射度降低了一个数量级，并相应地提高了源的亮度。这些设计的一个结果是大大缩短了电子束的寿命。这通常是通过使用谐波射频腔来拉伸电子束和降低粒子密度来补偿的。然而，一个缺点是发射的X射线脉冲比以前的设计变得更长，循环电子束的纵向动力学变得更加复杂。在此背景下，该项目的目的是研究如何最好地满足计时模式用户的需求，以钻石-II存储环为例，提出了三种可能的方法进行研究。第一种是使用混合填充模式，在环中填充一长串电子束，为大多数用户提供光，而在缝隙中填充单个电子束，用于研究依赖时间的现象。第二种是使用“共振激励脉冲拾取”，即使用快速磁铁来激发单个电子束中的垂直振荡。然后，来自这束光的光可以在空间上与剩余的光分开，以用于计时实验。最后一种方法是使用谐振腔来压缩电子束，而不是拉伸它们。这将缩短X射线脉冲长度，提高用户的时间分辨率。对于每种方法，都需要进行粒子跟踪研究，以调查电子对应用条件的反应，以便在电子变得不稳定之前确定平衡束的性质和最大电荷。

A step-change in the design of electron storage-rings for synchrotron light sources is currently underway. The latest structures consist of cells of magnets with multiple bending magnets which reduce the electron beam emittance by an order of magnitude and provide a corresponding increase in the source brightness. One consequence of these designs is a substantial reduction in the electron beam lifetime. This is typically compensated for by using harmonic RF cavities to stretch the electron bunches and reduce the particle density. One drawback however is that the emitted x-ray pulses become longer than in previous designs, and the longitudinal dynamics of the circulating electron bunches become more complex. Within this context, the aim of the project is to study how best to meet the needs of timing-mode users, taking the Diamond-II storage ring as an example.Three potential methods are proposed for study. The first is to use a hybrid filling pattern, in which the ring is filled with one long train of electron bunches to provide the light for the majority of users, and a single electron bunch in a gap for those studying time-dependent phenomenon. The second would be to use 'pulse-picking by resonant excitation', in which fast magnets are used to excite vertical oscillations in a single electron bunch. The light from this bunch can then be spatially separated from the remainder for use in timing experiments. The final method would be to use the harmonic cavity to compress the electron bunches rather than stretch them. This would reduce the x-ray pulse length, improving the temporal resolution for users. For each method, particle tracking studies are required to investigate how the electrons react to the applied conditions in order to determine the equilibrium bunch properties and maximum charge before it becomes unstable.