Thesis

Advanced modelling of Free-Electron Lasers : unaveraged simulations, sub-wavelength effects, and superradiant pulses saturation

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Awarding institution
  • University of Strathclyde
Date of award
  • 2025
Thesis identifier
  • T17206
Person Identifier (Local)
  • 201882454
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Department, School or Faculty
Abstract
  • This thesis presents the development and application of advanced computer simulation techniques for the study of cavity-based Free-Electron Lasers (FELs). The research integrates the unaveraged 3D FEL simulation code Puffin with the Optical Propagation Code (OPC) to enable the modelling of broadband, high temporal-resolution cavity FELs. This novel approach allows for the translation of radiation field formats between Puffin and OPC, facilitating the simulation of a Regenerative Amplifier FEL operating in the VUV range. Traditional simulation models for cavity-based FELs have averaged the optical field over an integer number of radiation wavelengths. This thesis, however, employs unaveraged simulation codes to model cavity-based FELs at the sub-wavelength scale. This enables the examination of effects such as Coherent Spontaneous Emission (CSE) from the electron beam and sub-wavelength cavity length detuning. The simulations reveal that for small sub-wavelength detunings, the FEL can preferentially lase at the third harmonic of the fundamental wavelength, suggesting new operational modes and potential applications for cavity-based FELs. Additionally, a detailed study is conducted on the saturation mechanism of a single superradiant spike of radiation in an FEL. Using a one-dimensional model developed with Puffin, the thesis demonstrates the sub-wavelength evolution of spike radiation and electron dynamics, leading to a highly non-linear saturation process. The study provides insights into the broad spectrum and high power of the saturated spike, with a proposed saturation mechanism validated by numerical results and simplified analysis of the 1D FEL equations. The combined use of Puffin and OPC codes represents a significant advancement in FEL simulation, enabling the exploration of unaveraged FEL and optical effects for the first time. This research not only enhances the understanding of fundamental FEL processes but also opens new avenues for further exploration and technological development in the field of Free-Electron Lasers.
Advisor / supervisor
  • McNeil, B.
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