A detector based on silica fibers for ion beam monitoring in a wide current range

A detector based on doped silica and optical fibers was developed to monitor the profile of particle accelerator beams of intensity ranging from 1 pA to tens of mu A. Scintillation light produced in a fiber moving across the beam is measured, giving information on its position, shape and intensity. The detector was tested with a continuous proton beam at the 18 MeV Bern medical cyclotron used for radioisotope production and multi-disciplinary research. For currents from 1 pA to 20 mu A, Ce3+ and Sb3+ doped silica fibers were used as sensors. Read-out systems based on photodiodes, photomultipliers and solid state photomultipliers were employed. Profiles down to the pA range were measured with this method for the first time. For currents ranging from 1 pA to 3 mu A, the integral of the profile was found to be linear with respect to the beam current, which can be measured by this detector with an accuracy of similar to 1%. The profile was determined with a spatial resolution of 0.25 mm. For currents ranging from 5 mu A to 20 mu A, thermal effects affect light yield and transmission, causing distortions of the profile and limitations in monitoring capabilities. For currents higher than similar to 1 mu A, non-doped optical fibers for both producing and transporting scintillation light were also successfully employed.