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On the theory and modelling of the fourth generation light source

Nam, Cynthia Kar Woon (2009) On the theory and modelling of the fourth generation light source. PhD thesis, University Of Strathclyde.

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Abstract

This thesis reports research carried out to develop a non-averaged 3D simulation code written using minimal approximation to model a Free Electron Laser (FEL) amplifier, the so-called fourth generation light source. Previous generations of light source use synchrotron which has poor temporal coherence. The current race to build the next generation of coherent light sources, FELs, has started and the work carried out in this thesis aims to provide a new simulation code to give insight on the behaviour of the electrons and radiation interaction below the radiation wavelength limit. The numerical simulation was written in Fortran 90 for use on parallel architecture computers to model a Free Electron Laser in three spatial dimensions and including time dependent effects. The Maxwell wave equation and Lorentz equation were used to describe the radiation field evolution and the electrons' propagation. These equations were scaled to become dimensionless. A finite element method, linear solver and Runge-Kutta method were applied to solve these equations. Previous results were reproduced in the 1D limit. Coherent Spontaneous Emission (CSE) was reproduced; this can not be done by other current 3D simulators. Other numerical studies include the FEL interaction, electron shot-noise and modelling of the energy spread and emittance of the electron beam. A final simulation demonstrates radiation difractive effects in a full nonlinear FEL interaction including all 3D effects. This code is the first of its type to be developed and will allow a completely new range of physics of the FEL to be investigated and exploited.