Perpendicular biased ferrite-tuned cavities

For varying the frequency of accelerating cavities in rapid-cycling RF systems for synchrotrons, perpendicular biased yttrium garnet ferrites have gained popularity over the conventional parallel biased NiZn ferrites. An important milestone in fast cycling perpendicular biased ferrite tuners was reached at TRIUMF in the spring of 1991. To the best of our knowledge this is the first time that anyone has operated a fast AC perpendicular biased yttrium garnet ferrite tuner over such a large frequency swing at high RF power levels. A similar design is now being developed at SSCL for the Low Energy Booster. This paper presents a brief history of the development of perpendicular biased ferrite tuners, a comparison of the two biasing; methods, magnetic field theory of perpendicular biasing, and the problem of eddy currents produced by the AC biasing circuit. A comparison is made of the requirements and design features of the different tuner designs with special emphasis on the designs in the process of being developed and tested