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.
| Date of Award | 31 Jan 2025 |
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| Original language | English |
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| Awarding Institution | - University Of Strathclyde
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| Supervisor | Brian McNeil (Supervisor) & Gordon Robb (Supervisor) |
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