Characterisation of Coherent Radiation in Short-Bunch Linac-Driven FELs

Abstract

A new CSR model implemented in the General Particle Tracer proposes the possibility of incorporating effects often ignored by other CSR models, such as effects arising from the transverse beam size and computation of CSR effects in the fringe region of a dipole field. Presented in this thesis are start-to-end simulations for both the CLARA Phase 1 beamline and the MAX IV linac. A reduction in the r.m.s energy spread of the electron bunch has been predicted in simulations arising from the velocity term of the Lienard-Wiechert field. This energy spread reduction occurs in the drift immediately following a dipole bend, and the effect has been shown to almost mitigate the energy spread induced by CSR in the dipole bend by ~20%. Further energy spread reductions have been shown in simulation by employing a scheme using strong focusing optics prior to a dipole bend in the presence of non-zero dispersion. A reduction in the r.m.s energy spread of 10 keV is observed across the first ~150 mm of the dipole bend. Measurements of fringe-field CSR emitted from a bunch compressor dipole on the MAX IV linac are compared to GPT CSR simulations. These measurements were collected using a photonic approach of inferring the energy loss of the bunch centroid from pyroelectric detection of THz radiation. Scans of several machine parameters, were carried out in order to provide several quantitative comparisons to the GPT CSR model. Two of the scans performed demonstrated very good agreement with the energy loss predicted by GPT simulations providing confidence in the novel effects observed in GPT simulations of the CLARA Phase 1 beamline. This study also presents the first comparison to the GPT CSR model carried out using direct measurements of the radiation.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Robert Appleby (Supervisor) & Hywel Owen (Supervisor)