Design and beam testing of a fast, digital intra-train feedback system and its potential for application at the International Linear Collider

Documented in this thesis is the development of the FONT5 beam-based, intra-train feedback system. It is designed to provide the beam stability at the interaction point of the International Linear Collider necessary to maintain a high luminosity. It has been possible to take advantage of the relatively large bunch spacing to implement a flexible system based around fast digital electronics, enabling additional features such as bunch train flattening and kicker droop compensation. A prototype feedback system has been installed at the Accelerator Test Facility in KEK, Japan, comprising three beam position monitors, two electromagnetic kickers and associated processing electronics. The installation is arranged to stabilise both the position and angle jitter of the beam in the vertical plane. Firmware for a Field Programmable Gate Array which runs the feedback algorithms is described, as are the results of a set of experiments to characterise the system behaviour. The feedback latency is measured to be 135 ns for position feedback alone, and 147 ns when operating in both degrees of freedom. Using a three-bunch train with spacing of 154 ns, a vertical position stability of 430 nm in the feedback BPM is achieved. This is seen to fulfil the requirements of the International Linear Collider intra-train interaction point feedback system, even if the machine were to operate with the proposed ‘Low-N’ parameter set where the bunch spacing is 50% of nominal. A statistical framework is developed to help understand the operation of the feedback upon trains with imperfect bunch-to-bunch position correlation, and is applied to the results of the FONT5 experiments. In this way, the prospect of using the prototype FONT5 installation to help meet the goals of the ATF2 final-focus test beamline is considered.