APPLICATIONS OF FERRITES AND FERROMAGNETS IN TUNING RF CAVITIES FOR ACCELERATORS

Traditionally ferrites have been used in accelerators for tuning rf ca vities and in nonreciprocal devices controlling the power flow in rf a ccelerating systems. Recently, the development of cavity tuners based on perpendicularly biased ferrites has shown good progress. Yttrium ir on garnet (YIG) is gradually replacing the traditional Ni Zn ferrites. The use of conventional parallel-biased Ni Zn ferrites for varying th e frequency of accelerating cavities has the disadvantage of high satu ration magnetization (4piM(s)). This precludes practical operation in low magnetic loss regions. Different substitutions have been used with YIG to reduce its 4piM(s), making it a practical candidate for perpen dicular biasing operating in the saturation region. In addition, YIG i s known for its low dielectric and magnetic losses. In this paper we g ive a short review of development in accelerator cavity tuners based o n perpendicularly biased iron garnet ferrites. We use the operation of a 52 MHz stripline-based YIG tuner which we have tested at BNL as an example to demonstrate the advantages of using YIG in cavity tuners. W e also discuss magnetic tuning techniques based on magnetostriction of Ni.