Cavity Beam Position Monitors State of the Art and Design Studies in the Context of the ILC Project

Abstract: The aim of this master thesis project is the study and evaluation of the design of cavity beam position monitors (BPM) for the International Linear Collider (ILC) project. The state-of-the-art of BPMs is investigated to determine the most appropriate existing BPM design for the requirements of the ILC. The theoretical background on resonant cavities, including the beam coupling to the BPM, is examined. This knowledge enables the understanding of how certain parameters can affect the performance of the detector. To this end, a design investigation is carried out by analyzing the frequency spectrum of the beam for choosing the operational frequency of the resonator. Different common-mode-rejection methods are evaluated as well. Theoretical predictions are confirmed by 3D electromagnetic simulations, with the commercial software CST, based on a basic design of cavity BPM. The simulations are also performed in order to understand the impact of the cavity geometry on the BPM. The identication of the dipole mode signal for an offset beam corroborates the working principle of the cavity BPM. The particle-in-cell (PIC) solver from CST is revealed to be the most adequate for the simulation of the cavity BPM, allowing an efficient extraction of the dipole field induced by the beam. The state-of-the-art and the numerical results support the design of a cylindrical cavity with operational frequency of 1.495 GHz, with rectangular waveguides output ports used as filters to reject the monopole mode signal.