Novel hybrid multipolar RF cavities for transverse beam manipulations

Thesis

This thesis describes the development and application of a method for tailoring the profile of electromagnetic fields in RF cavities for use in particle accelerators. This so-called azimuthal modulation method (AMM) is underpinned by an analytic expression of the basis of the electromagnetic modes in closed RF cavities whose cross-sections vary with the azimuth. This basis is derived and the notation {M}ηp is introduced to describe the azimuthal, radial and longitudinal form of the modes.

The scope of the AMM for designing realisable cavities is explored. The underlying reasons for the limitations on the range of magnitudes and orientations of multipoles that can be supported by azimuthally modulated cavities are derived and discussed.

This understanding provides the foundation for the latter half of the thesis where numerous applications of the AMM are presented. First, the AMM is used to construct a prototype cavity that supports a 3 GHz mode which could be used for the simultaneous acceleration and focusing of a particle beam. Experimental testing supported the multipolar content of the mode being as designed. Second, the AMM is applied to create RF cavities which support modes free from unwanted multipoles generated by power couplers and tuning pins. An example design of an RF structure which incorporates a single-slot power coupler and supports an accelerating mode free from dipole, quadrupole, sextupole and octupole components is analysed. Third, the AMM is used to design RF cavities that support modes tailored for the off-axis traversal of particle beams. An example optimisation of an accelerating field that remains as flat as possible along the horizontal is presented. Finally, the AMM also finds application in the creation of musical drums. This concept inspired an outreach workshop that was designed and delivered to showcase this research to 11-14 year-old school students.

Authors: Wroe, L

• DOI: 10.5287/ora-r50ab09gg
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: accelerator physics; RF cavities; multipole expansion; electromagnetic fields
• Subjects: Particle accelerators; Physics