Design and Optimisation of High-Energy Inverse Compton Scattering Sources Driven by Multi-Pass Energy Recovery Linacs

Abstract

High quality x-ray sources are required for fundamental research in atomic physics and material science. Third generation synchrotron light sources fulfil this need in most aspects, producing a high flux with x-ray energies up to 100's~\si{\kilo\electronvolt} and a narrow bandwidth . However, the maximum photon energy produced by synchrotrons is limited by facility size, electron beam energy and magnet strength constraints. Hence, in this thesis an inverse Compton scattering (ICS) source has been designed for production of high energy x-rays ($E_{\gamma} \leq 402.5$~\si{\kilo\electronvolt}) from the CBETA multi-turn energy recovery linac (ERL), with high flux ($\mathcal{F} = 3.22\times 10^{10}$~ph/\si{\second}) and narrow bandwidth ($\Delta E_{\gamma}/E_{\gamma} = 0.5$\% rms). Similarly, high quality $\gamma$-ray sources ($E_{\gamma} > 1$~\si{\mega\electronvolt}) are in demand for experimentation in nuclear photonics, photonuclear radioisotope production, nuclear forensics and proliferation. Whilst bremsstrahlung and radioisotope $\gamma$-ray sources could be used, they are not ideal as bremsstrahlung is inherently broadband and radioactive isotopes produce a low flux. Currently ICS sources, such as HI$\gamma$S, produce $\gamma$-rays up to 100~\si{\mega\electronvolt} with high photon fluxes ($\mathcal{F}=5\times 10^{8}$~ph/\si{\second}), however the bandwidth ($\Delta E_{\gamma}/E_{\gamma} = 2.5$\% FWHM) is too large for some experiments. Hence, the DIANA ERL driven ICS source is designed to provide narrowband ($\Delta E_{\gamma}/E_{\gamma} = 0.5$\% rms) $\gamma$-ray production ($E_{\gamma} \leq$ 20.11~\si{\mega\electronvolt}) at higher flux ($\mathcal{F} = 6.08\times 10^{10}$~ph/\si{\second}). Various accelerators can provide electron beams to drive ICS sources, though large scattered photon fluxes require a high average electron beam current and small emittance, whilst narrow bandwidths require small emittance and small electron beam energy spreads. Therefore, this thesis develops optimisation methods for ICS production of narrow bandwidth photons at high flux. Currently, most ICS sources utilise storage rings, with high average beam current and moderate electron bunch energy spread, or linacs, with small emittance and energy spread. ERLs can provide electron beams with small emittance, energy spread and high average beam current simultaneously. Hence ERLs are ideal drivers of ICS sources. In this thesis two ICS sources are designed: the CBETA x-ray ICS source and the DIANA $\gamma$-ray ICS source. Methods for predicting the flux and the produced photon spectrum are developed and a series of optimisations toward maximal narrowband photon production are proposed. Applications of the produced narrow-band, high energy photons are then investigated for x-rays and $\gamma$-rays and photon production from ERL driven ICS sources is compared with other light sources.

Date of Award	1 Aug 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Guoxing Xia (Supervisor) & William Bertsche (Supervisor)