Tuning system for capacitively loaded 1/4 accelerating cavity

The Brookhaven National Laboratory NSLS X-ray and vuv rings currently use capacitively loaded lambda/4 RF accelerating cavities. These cavities are manufactured from copper clad plate steel and require a tuning system with a considerable range. Three separate tuning systems are provided, each having its own specific problems, and interactions occur between the three systems. A single capacitive tuning system is proposed which will vary the capacitance loading of the cavity directly. The system employs a vacuum balance mechanically driven diaphragm. The control system allows 6 mm of motion at a maximum slewing rate of 1.0 mm per sec and yields a dynamic tuning range of 480 kHz. Design and fabrication details are presented together with early testing and operating experience.