  Detectors planned for use at the Large Hadron Collider will operate in a
radiation field produced by beam collisions. To predict the radiation damage to
the components of the detectors, prototype devices are irradiated at test beam
facilities that reproduce the radiation conditions expected. The profile of the
test beam and the fluence applied per unit time must be known. Techniques such
as thin metal foil activation and radiographic image analysis have been used to
measure these; however, some of these techniques do not operate in real time,
have low sensitivity, or have large uncertainties. We have developed a
technique to monitor in real time the beam profile and fluence using an array
of $p-i-n$ semiconductor diodes whose forward voltage is linear with fluence
over the fluence regime relevant to, for example, tracking in the LHC Upgrade
era. We have demonstrated this technique in the 800 MeV proton beam at the
LANSCE facility of Los Alamos National Laboratory.
