A PROGRAMMABLE DSP-BASED NEUTR

Abstract
Neutron choppers at spallation-neutron facilities are
rotating devices that are precisely phased to chop a
neutron beam.? Depending on the mass, moment-of-
inertia, and velocity of rotation, a chopper can have a
large amount of stored kinetic energy.?? For example, the
PHAROS T-zero chopper at the LANSCE facility at Los
Alamos National Laboratory has a rotating kinetic energy
of over 1 MJ.? When energy levels are this high and for
other logistical reasons, it is often much more practical to
develop and test chopper speed and phase controllers
using a hardware simulator than an actual chopper.? This
paper describes the design and performance of a
programmable DSP-based chopper simulator developed
and used at LANSCE.?? Chopper models are first
developed using Simulink and then coded for uploading
to the DSP.? Several chopper models have been developed
all of which include moment-of-inertia, losses, motor
parameters, and rotating speed.? The simulator receives, as
input, an analog control voltage and outputs a digital top-
dead-center (TDC) pulse train.