Design and Analysis of the Medium-β Elliptical Cavities for the European Spallation Source Accelerator

Sammanfattning: This thesis is dedicated to the design and analysis of superconductingelliptical cavities. Elliptical cavities play a central role in modern particle ac-celerators due to their high efficiency. After an introduction to the EuropeanSpallation Source project, the thesis goes through the design of the medium-βcavity. The RF design of the inner cell and end cell are presented in sequencein paper I . The design is completed by the chapter on the mechanical perfor-mances of the cavity (paper II).Papers III, IV and V are instead dedicated to the analysis of the cavity.The necessary mathematical tools for the analysis are presented in paper IIIwhich, after stating fundamental results on hollow cavities, presents a spec-tral decomposition used in the following papers. In paper IV, a time-domainmodel for the power dissipation induced by the excited higher-order-modes ispresented. Such modes are excited by the particle beam that passes throughthe cavity and are detrimental to the performances of the accelerator. PaperV presents a time-domain model of the cavity coupled to an externa circuit toa coupler. The model is functional to the design of the cavity control system.