X-Ray Free Electron Lasers

X-ray Free-Electron Lasers (XFELs) are large-scale accelerator facilities generating radiation beams with intensity far exceeding that of any other available source of high-energy photons. The beams from an XFEL have important applications across a broad range of science: for example, they can be used to determine the detailed structure of complex biological structures such as

proteins and viruses, and to observe with unprecedented detail the processes taking place (on timescales of order 10-15 seconds) in chemical reactions. XFELs are essential tools for research in many different fields, including the life sciences, materials science and physical sciences.

However, effective operation of an XFEL requires extremely precise control of the high-energy electrons used to generate the photon beams. A wide range of effects in the systems used to accelerate and manipulate the electron beams can easily degrade the quality of the electron and, consequently, the photon beams. The magnets used to steer and focus the charged particle beams and (ultimately) to generate the photon beams play a critical role in achieving and maintaining the necessary electron and photon beam quality.

Conventional accelerators have generally relied on a few standard types of magnet for control of charged-particle beams. Typically, accelerator magnets are designed so that the field varies in a simple way in directions perpendicular to the beam motion, and is independent of distance along the magnet in a direction parallel to the beam motion. However, as machines and facilities become more ambitious in terms of beam parameters, more exotic magnet designs are being explored.

A further issue in any high-energy particle accelerator is that relativistic effects mean that any manipulation of the particle beams usually requires large magnets with strong fields, arranged over large distances (tens or hundreds of metres in the case of a high-power XFEL). The greater design flexibility in novel accelerator magnets offers the potential to reduce the scale of high-energy particle accelerators, making the facilities easier and cheaper to build, as well as enabling higher levels of performance.

The research that will be carried out for this PhD project will build on existing studies in the Cockcroft Institute related to magnet design, to the modelling of beam dynamics in advanced accelerator systems, and to the design of XFEL subsystems (used, for example to reduce the lengths of individual bunches of electrons, and to direct the bunches to any of a range of beamlines where the X-rays are produced). As well as developing novel tools and techniques for tailoring

magnet designs to specific requirements for the beam dynamics (including techniques based on machine learning), the student will apply advanced simulation codes to gain an insight into how different features of accelerator magnets affect electron beam properties. The work carried out will be of interest for existing and future XFEL facilities, including new machines and those with long-term upgrade plans.

The improved understanding of beam dynamics in novel magnets and the associated development of advanced design techniques will also have wide benefits for many different types of accelerator.