FRIB, East Lansing, Michigan, USA
The Facility for Rare Isotope Beams tunes the beam power from 0 to 400KW by chopping the beam current with a beam chopper in the Low Energy Beam Transport. A chopper monitoring system is employed to verify proper chopper operation to avoid delivery of undesired high-powered beam and to inhibit beam for machine protection purposes. The system monitors the incoming beam gate time structure, the chopper switch high voltage pulses, the chopper electrode charge/discharge currents, and the status of machine protection system. It is designed to switch off the beam within tens of nanoseconds of a detected fault. Chal-lenges include a dynamic beam gate pulse structure with pulse lengths as short as 0.6 µs and high voltage power supply current pulses of ~25 ns. A high speed "integrate and hold circuit with reset", Field Program-mable Gate Array based digital control circuit and high speed ADC circuit were developed to fulfil the re-quired functions. Design approach, simulation, and test results with the beam are the focus of this paper.
