High-Q toroidal cavities for high frequency klystrons

A toroidal cavity developed for a 4-KW 12 GHz satellite-borne television transmitter klystron is described. The cavity has an internal Q 40 percent higher than that of a conventional cylindrical doubly-reentrant cavity, thus yielding higher circuit efficiency and conserving energy which cannot be recovered in multi-stage depressed potential beam collectors. As a result of optimization studies with a digital computer program for obtaining cavity field distributions by a relaxation method and for computing the intrinsic cavity parameters R/Q and Q δ/λ (where R is the cavity interaction gap shunt impedance, Q the cavity bandwidth parameter f/Δf, and δ/λ the skin-depth to wavelength ratio), a particular cavity configuration with conical reentrant tunnel tips and toroidal walls is shown to provide good thermal characteristics and mechanical rigidity as well as low internal losses. Methods of die-coining toroidal cavities for centimeter and millimeter wavelength klystrons are described and a comparison between theoretically predicted and experimentally measured properties of toroidal cavities is given.