Pulsed ferrite core tests for 50-ns linear induction accelerator

The Lawrence Livermore Laboratory undertook an investigation of the properties of ferrite materials to be used in a 5-MeV, 50-ns linear induction accelerator. The investigation, on a part-time basis, lasted about one year and had the cooperation and helpful suggestions of several manufacturers: TDK of Japan, Phillips of Holland, and Stackpole of the U.S.A. Ferrites have been widely used as tuning cavities for proton synchrotron accelerators at radio frequencies. In such an application, the μQf factor is used in describing the figure of merit for ferrites where a high duty factor requires low loss ferrites. In our linear induction accelerator with an average rep-rate of 5-Hz, the ferrite losses are negligible and the concept of complex permeability in describing the losses will not be introduced, but a large signal ΔB/ΔlH will be used to describe their properties. The properties of interest in designing the accelerating cavity were: a) flux swing ΔB = Br+ Bm> .5T b) a residual flux density with a reset no greater than 2 Oer. c) a relatively high incremental μ > 400 to keep the excitation current small in relation to the load current, d) a high resistivity for the 250-kV voltage hold-off.