Design of an electron beam stabilisation controller for a synchrotron

• A control design for synchrotron electron beam stabilisation is presented.
• The controller was implemented at a synchrotron and machine data is presented.
• Controller parameters chosen based on trade-off between robustness and performance.
• Fourier modal decomposition used to analyse robust stability.
• Selecting different dynamics on each mode gives enhanced performance.

Synchrotrons are used to generate light for academic and industry research by accelerating electrons travelling in a circular path to relativistic speeds. In order to achieve optimum performance, electron beam stability is a crucial parameter for synchrotrons. This paper describes the design of a beam stabilisation controller, using Internal Model Control. Basis functions are used to identify the controllable components of the system and it is demonstrated how by selecting dynamics for each spatial mode, enhanced performance is achieved. The robust stability of the controller in the presence of spatial uncertainties is developed within an Integral Quadratic Constraint framework using two methods of spatial decomposition: Singular Value decomposition and Fourier decomposition. The controller has been implemented at Diamond Light Source, the UK׳s national synchrotron science facility. Results from the controller implementation are presented and it is demonstrated how the controller design and robust stability analysis are used to tradeoff performance and robustness.