Application of the Two-Power-Supply Method to the Ferrite Bias of an RF Resonator of a Rapid-Cycling Synchrotron

Abstract

Ferrite bias equipment for the RF resonators of high-repetition-rate synchrotrons is expensive because of the high voltage necessary to overcome the back EMF of the unsaturated ferrite at the beginning of the sweep and the high current necessary to saturate the ferrite at the end of the sweep. The high-frequency resonators of the Omnitron, which sweep in 8 ms require 70 V initially, but only 20 V after the second millisecond, when the current reaches 5 kA. The voltage remains low for the remainder of the sweep, while the current increases to 20 kA. To meet these requirements as inexpensively as possible, a pulse-type power supply is used during the first 2 ms, and a high-current power supply through the remainder of the sweep. Smooth current transfer is an inherent property of the circuit. Inductance, which is surprisingly costly, is kept to a minimum by a sandwich bus bar technique. A silicon-controlled rectifier (SCR) switch reverses the current every other sweep so that the full hystereses loop of the ferrite is used. A regulator circuit forces the bias current to follow a reference pulse.