A 40-Kilovolt, 125-Ampere Hard Tube Modulator for Accelerator Service

A hard tube modulator designed to generate a 40-kilovolt pulse at 125 amperes for 2 milliseconds at 6% duty factor has been constructed. The rise and fall times will be controlled and the flat top regulated to program requirements. The Machlett NL-LPT 14 was used for the switch tube in this application utilizing magnetic focusing with a coarse grid structure and multiple cathode beams to achieve low grid drive with high plate efficiencies. Low grid drive allows simplification of the drive to one tube driven directly from the rectified rf control signal. The rf control signal at 4.8 Mc is coupled across the high voltage interface through a ferrite core transformer.