Beam Loading Studies for Cavity Phase and Amplitude Setting

Abstract: The purpose of this thesis is to study beam-cavity interactions, with a focus on how to maintain an unperturbed acceleration field in a conducting cavity with a proton beam present. The impact on a cavity acceleration field from different perturbation sources is investigated through computer simulations of a theoreti- cal model based on a resonant circuit. Perturbations from the RF input pulse to the cavity, from the cavity field control system and from the proton beam pulse shape are investigated. The cavity field control system is dependent on accurate measurement of the beam phase and accelerator operation requires accurate measurements of the beam position. Therefore the thesis also aims to analyze the limitations of beam position monitors (BPMs) in detecting the phase and position of the proton beam, and to analyze and identify relative performance degradation of beam phase de- tection when measuring a low current beam with varying pulse length. This is done through measurements on a scale model of a pipe section with BPMs. The theory section gives an overview of the cavity model, cavity beam load- ing, beam position monitoring and phase scan theory. RF input pulses that gener- ates the required cavity field while fulfilling cavity perturbation criteria are iden- tified. Finally the thesis attempts to improve linear accelerator performance by finding RF input pulses and cavity settings that minimize energy consumption while also fulfilling the requirements for cavity field stability and BPM accuracy.