Development and test of a beam imaging system based on radiation tolerant optical fiber bundles

Many of the beam imaging systems at CERN are located in high radiation environments. In order to cope with this issue, VIDICON cameras are presently used, but their production has been discontinued worldwide. This paper presents the development of an alternative beam imaging system, based on radiation tolerant optical fibre bundles. The fibre bundle is used to relay the image of a scintillating screen to a standard CMOS camera, located away from the high radiation zone. A prototype system based on a 10m long bundle with 10$^4$ fibres has been tested in the laboratory by simulating the beam profile using a laser spot. The light transmission through the system is rather low, but is compensated by the high sensitivity of the CMOS camera. The tested system had a field of view of 60 mm and a spatial resolution of ~1 mm. The radiation hardness of the fibre bundle was tested at the IRMA-CEA facility in Saclay, France. The bundle was irradiated at a rate of 3.6 kGy/h for 8 consecutive day. The total integrated dose achieved was ~700 kGy, which corresponds to about ten years of operation at the beam imaging station with the highest radiation dose at CERN. Although the light transmission was reduced by 50% after irradiation, this is still sufficient for our purpose.