Trigger control and fault reaction circuitry for the solid-state switch modulator deck at the MIT-Bates S-band transmitter

This paper describes the trigger control and fault reaction circuitry for the new solid-state switch modulator at the MIT Bates Linear Accelerator Center. This new circuitry has been designed and built to control the new cathode-switching solid-state modulator that replaces the old vacuum-tube technology modulator. The old modulator used a start signal to commence its pulses and a separate stop signal to end its pulses. The new system uses a single gate signal to control the modulator pulse. The trigger control circuit is a stand-alone control unit that can operate in a local (manual) mode or a remote mode. In the local mode the unit uses its own oscillator to run the transmitter. In the remote mode the accelerator-control computer can turn triggers on or off (enable the triggers), can reset the unit, and can send the gate signal that triggers the modulator. There is no microprocessor fault control of the transmitter. The trigger control chassis receives all necessary signals from the transmitter and performs all necessary trigger control and fault reaction functions by itself. These fault reactions can be to turn off the solid-state switch, to fire the crowbar, or simply to light LEDs. The main accelerator-control microprocessor receives report signals from the trigger control unit to alert the accelerator operators to the status of the transmitter. The trigger control circuitry limits the modulator pulse width to 5 microseconds longer than the gate signal up to a maximum of 55 microseconds and limits the pulse repetition frequency to under 2 kHz. All the circuitry is designed with noise suppression techniques and with a high level of noise immunity (5 volts or more) to ensure fault-free operation in a noisy, transient-filled environment.