Anode modulation of high power RF output triodes of the ISIS linac

The ISIS Linear Accelerator at Rutherford Appleton Laboratory (RAL) has provided acceleration of H^- ions since 1984. ISIS has recently replaced the first pair of legacy, low power cathode modulators used on its 2 MW RF triodes with high power, solid-state anode modulators. The key to these new modulators is a series IGBT high voltage switch, rated at up to 40 kV, 300A, built by Diversified Technologies, Inc. This new modulator has eliminated a number of operating difficulties, and yielded significant savings with regard to operational downtime and ~25% energy consumption. These advantages benefit ISIS by improving reliability and availability, and ensuring RAL´s push towards an increased proton beam current above 200 μA can be achieved. This paper describes the modulator design, installation, and performance in the Linear Accelerator, as well as our operational experience since the first two units were installed in 2012.