An energetic charged particle beam introduced to an rf cavity excites a wakefield therein. This wakefield can be decomposed into a series of higher order modes and multipoles, which for sufficiently small beam offsets are dominated by the dipole component. This work focuses on using these dipole modes to detect the beam position in third harmonic superconducting S-band cavities for light source applications. A rigorous examination of several means of analysing the beam position based on signals radiated to higher order modes ports is presented. Experimental results indicate a position resolution, based on this technique, of 20 microns over a complete module of 4 cavities. Methods are also indicated for improving the resolution and for applying this method to other cavity configurations. This work is distinguished by its clarity and potential for application to several other international facilities. The material is presented in a didactic style and is recommended both for students new to the field, and for scientists well-versed in the field of rf diagnostics.
About the Author
The author read physics at the University of Science and Technology of China (USTC) in Hefei from 2002 to 2006. After graduating with a BSc in applied physics, he worked at CERN in Geneva for one year as a visiting scholar employed by the University of Michigan (Ann Arbor). In 2009, he was awarded a MSc in Particle Physics from USTC. Subsequently he joined the accelerator group at the University of Manchester to pursue a Ph.D. and was based at DESY (Hamburg). After successfully defending his Ph.D. thesis in December 2012, he joined the BE-RF group at CERN as a Marie-Curie Experienced Researcher.
Table of ContentsIntroduction.- Electromagnetic Eigenmode Simulations of the Third Harmonic Cavity.- Measurements of HOM Spectra.- Analysis Methods for Beam Position Extraction from HOM.- Dependencies of HOM on Transverse Beam Offsets.- HOM-Based Beam Position Diagnostics.- Conclusions.- Bibliography.- Mathematics.- Eigenmodes of an Ideal Third Harmonic Cavity.- Technical Details of the HOM Measurements.