A comparative study of the existing methods for their suitability to beam stabilization in Storage Ring at Canadian Light Source

Abstract

The stabilization of electron beam in the Storage Ring (SR) is an important task in the 3rd generation synchrotron facility worldwide. Deviations in the position and angle of electron beam with respect to a desired orbit must be below 10% of the beam size. This requirement corresponds to about 3 μm deviations at the Canadian Light Source (CLS). Further, the higher the correction bandwidth, the better in the stabilization process. The correction bandwidth at CLS was expected to increase to be 45 Hz or higher from the current operating rate at 18 Hz. In addition, there is requirement to control the beam deviation at specific positions on the orbit. To meet these requirements, a comparative study of the existing methods for the stabilization of electron beam in the SR is thus necessary, which is the main motivation of this thesis study.

The overall objective of this thesis study was to find the most suitable method for CLS so that the correction bandwidth can be 45 Hz or higher. The study was primarily conducted by simulation due to the restriction in performing experiments on the whole beamline. The transfer functions of three important devices at the storage ring, which are Beam Position Monitor (BPM), Orbit Correction Magnets (OCM) and Vacuum Chamber (VC), were identified. Noises on the storage ring were also identified to improve the reliability of the simulation study. The existing methods for beam orbit correction, such as (1) Singular Value Decomposition (SVD), (2) Eigen Vector method with Constraints (EVC) and (3) SVD plus Proportional integral derivative (PID), were compared based on the simulation technique.

Several conclusions can be drawn from this study: (1) there is no significant difference between the EVC method and SVD method in terms of overall orbit correction performance, and they both can meet the correction bandwidth of 45 Hz. The EVC method is however much better than the SVD method in terms of the beam orbit correction performance at specific positions; (2) the SVD plus PID method is much better than the SVD method as well as EVC method in terms of the overall orbit correction performance, and its performance for specific position orbit correction is comparable with the performance of EVC. Therefore, the SVD plus PID method is recommended for CLS.

This study has made the following contributions on the problem of beam stabilization the storage ring in the synchrotron technology: (1) provision of the models of BPM and OCM and the PID controller tailored to specific BPM and OCM devices, which is useful to other synchrotron facilities in the world; (2) generation of the knowledge regarding the performances of SVD, EVC and SVD plus PID methods on one synchrotron facility is valuable, and this knowledge is useful to other synchrotron facilities in selection of the best methods for electron orbit correction.