Microbunching Instability Suppression for Improved FEL Performance

自由电子激光器（FELs）是第四代光源，能够产生宽波长范围的辐射，同时产生飞秒（10-15秒）脉冲。这使得从材料科学到生物学等多个领域的研究人员能够以高分辨率探测原子尺度结构和动态过程。开发更亮、脉冲时间更短的电子脉冲使这些研究人员在医学、生物学和材料科学方面取得了迫切需要的进步。随着对更亮的自由电子激光（FEL） x射线需求的增加，对高质量电子束和更高峰值电流的需求也在增加，然而，有各种各样的影响使得实现这些要求变得困难。微聚束不稳定性（MBI）和相干同步辐射（CSR）干扰是导致发射度增加和felo性能下降的效应。本项目将通过几个目标来研究微束不稳定性和扭曲的CSR踢球，将在下面进行总结。CSR是发生在偶极子中的一种现象，在偶极子中，相对论性粒子，如电子，相干辐射。当这种辐射被束中的其他粒子吸收时，能量就会沿着束重新分布。这导致束的纵向切片在横向坐标上偏移，因此增加了投射发射度。目前有一些ecsr抵消技术用于最小化这种影响，但如果CSRkicks在非色散部分被偶极子扭曲，这些技术可能效果较差。本文将研究导致扭曲的CSR踢腿的条件，并研究CSR对消技术对扭曲踢腿的有效性。微聚束不稳定性是由线性加速器色散区由CSR引起的小的初始能量调制引起的电流密度调制（或微聚束）。一种称为焦散的奇点可以用数学方法描述微聚束动力学。该项目旨在通过设计一个实验来测量瑞典隆德MAX-IV的焦散感应电流尖峰的演变，从而在直线加速器中获得粒子轨迹焦散的首次实验测量。阈值R56对微束增益的作用也可以进行调查，因为两者之间的关系尚未完全理解。更好地了解CSR和微束不稳定性，将使我们能够抑制不良影响并保持光束质量，最终实现更亮的feles光源。

Free Electron Lasers (FELs) are a fourth-generation light source capable of producing radiationover a broad range of wavelengths, while producing femtosecond (10-15 second) pulses. This allowsresearchers across several fields, from materials science to biology, to probe atomic scale structuresand dynamical processes with a high resolution. Development of brighter FELs with shorter pulsedurations allows these researchers to make much needed advancements in medicine, biology andmaterials science.As demand for brighter Free Electron Laser (FEL) X-rays increases, so does the need for highquality electron beams and higher peak currents, however there are various effects which makeachieving these requirements difficult. Microbunching instability (MBI) and Coherent SynchrotronRadiation (CSR) kicks are the effects which lead to increased emittance and decreased FELperformance. This project will investigate microbunching instability and distorted CSR kicksthrough a few aims, which will be summarised below.CSR is a phenomena that takes place in dipoles where relativistic particles, such as electrons,radiate coherently. When this radiation is absorbed by other particles in the bunch, there is aredistribution of energy along the bunch. This leads to longitudinal slices of the bunch being offsetin the transverse coordinates, and therefore increased projected emittance. Currently there are someCSR cancellation techniques used to minimise this effect, but these may be less effective if the CSRkicks are distorted by dipoles in non-dispersive sections. The conditions which lead to distortedCSR kicks will be investigated and the effectiveness of CSR cancellation techniques on distortedkicks will be studied.Microbunching instability arises from small initial energy modulations induced by CSR leading tocurrent density modulations (or microbunching) in the dispersive regions of a linear accelerator(linac). A type of singularity known as caustics can be used to mathematically describemicrobunching dynamics. This project aims to obtain the first experimental measurements ofparticle trajectory caustics in a linac, by designing an experiment to measure the evolution ofcaustic-induced current spikes at MAX-IV, in Lund, Sweden. An investigation into the role ofthreshold R56 on microbunching gain can also be made, as the relationship between the two is notcompletely understood. Better understanding of CSR and microbunching instability, will allow us tosuppress the undesirable effects and preserve beam quality and ultimately allow for brighter FELsources.