Feedback Systems for Linear Colliders

Feedback systems are essential for stable operation of a linear collider, providing a cost-effective method for relaxing tight tolerances. In the Stanford Linear Collider (SLC), feedback controls beam parameters such as trajectory, energy, and intensity throughout the accelerator. A novel dithering optimization system which adjusts final focus parameters to maximize luminosity contributed to achieving record performance in the 199798 run. Performance limitations of the steering feedback have been investigated, and improvements have been made. For the Next Linear Collider (NLC), extensive feedback systems are planned as an integral part of the design. Feedback requirements for JLC (the Japanese Linear Collider) are essentially identical to NLC; some of the TESLA requirements are similar but there are significant differences. For NLC, algorithms which incorporate improvements upon the SLC implementation are being prototyped. Specialized systems for the damping rings, RF and interaction point will operate at high bandwidth and fast response. To correct for the motion of individual bunches within a train, both feedforward and feedback systems are planned. SLC experience has shown that feedback systems are an invaluable operational tool for decoupling systems, allowing precision tuning, and providing pulse-to-pulse diagnostics. Feedback systems for the NLC will incorporate the key SLC features and the benefits of advancing technologies. 1 OPERATIONAL ISSUES Linear colliders have severe operational challenges, and feedback systems are an essential tool. Feedback systems distributed throughout the machine allow less-invasive tuning procedures, so that when upstream parameters are modified, downstream feedback stabilizes the beam, allowing routine operation to continue. Feedback is also invaluable in facilitating quick startup after outages. A robust design ensures that the feedback is not confused when the beam returns after an outage, and that control devices are not moved in the absence of beam. Feedback is a useful element in higher-order tuning applications. In the SLC linac, the emittance tuning packages move feedback setpoints to create an oscillation in the linac which is closed by a downstream feedback. In the _______________________ Work supported by the U.S. Dept. of Energy under contract DE-