Diagnostics and control of transverse coupled-bunch instabilities in third generation electron storage rings

© 2011 Dr. David PeakeThe Australian Synchrotron is a newly commissioned third-generation light source situated in Melbourne, Australia. Synchrotron radiation is produced from the 216 metre circumference storage ring where 3 GeV electrons are trapped within a lattice formed by dipole bending magnets and multipole focussing magnets. The appearance of coupled-bunch instabilities form the primary limitation of modern storage rings. Instabilities enforce an upper limit on stored current and can reduce the utility of radiation production by increasing the effective emittance of the ring. Stored current limitations due to beam instabilities were discovered early in the commissioning phase of the Australian Synchrotron storage ring and were initially controlled by substantially increasing the chromaticity of the lattice from (ξx; ξy) = (2; 2) to (ξx; ξy) = (3:5; 13). Subsequent additions to the ring have resulted in an increase of the strength of destructive instabilities to the point where detrimental side-effects from chromatic corrections reduce the ability of the ring to damp instabilities. This increase in instability strength has lead to the shift from purely passive methods of instability control to the design and construction of an active transverse feedback system. This thesis describes the commissioning of a bunch-by-bunch transverse feedback system designed to combat coupled-bunch instabilities, allowing for the reduction of chromaticity within the storage ring lattice back to the initial design values (ξx; ξy) = (2; 2). Reducing the chromaticity also removes detrimental effects such as the reduction of the dynamic aperture and an increase in the lifetime of the beam. Novel methods for tuning the system and maximising the damping rate of the beam are introduced. Using these methods, the feedback system was successfully commissioned and was shown to have the stability required for user-mode storage ring operations. The bunch-by-bunch transverse feedback system can also be leveraged as a powerful diagnostic tool. New data acquisition techniques have been designed to allow for the study of different instability mechanisms as well as parameters present in the equations of motion for stored particles. These techniques and the suite of results achieved are presented