A solid-state push-pull grid driver for high power tetrodes

Summary form only given as follows. A new push-pull solid-state grid driver design has been developed at General Atomics for use in high power modulator/regulators (mod/reg) utilizing vacuum tetrodes. The project, part of a purchase contract with a fusion research facility, culminated in the delivery of three operational grid drivers. The grid driver provides the voltage control for the operation of a power vacuum tetrode used in a series regulator topology. The grid driver´s feedback loop is closed on the power vacuum tetrode output voltage. In the described application, the grid driver was specified for operation in a mod/reg utilizing the CPI 9009 power vacuum tetrode. Grid driver performance specifications included 0 V to -950 V DC dynamic output voltage range with 300 W continuous rating at maximum voltage and a bandwidth of 20 kHz. High voltage MOSFET semiconductors (APT1001RBN) were used in a push/pull configuration to achieve a 20 kHz bandwidth and an open loop voltage slew rate of 100 V/ms into a 700 pF load. A next generation grid driver design with 1.5 kV DC output voltage capability is in development and is also presented. This grid driver design will be used in mod/regs supplying cathode gun voltages to 110 GHz, 1 MW gyrotrons used in the DIII-D National Fusion Facility. Of particular interest in the grid driver designs are voltage isolation techniques between the grid driver control circuit and the high power vacuum tetrode including the use of fiber optics, isolation amplifiers, and isolated printed circuit board traces. Printed circuit board layout and critical component selection for use in a high noise environment are also discussed