Multianode Photo Multipliers as Photo Detectors for Ring Imaging Cherenkov Detectors
The 64-channel Multianode Photo Multiplier (MaPMT) has been evaluated as a candidate photo detector for the LHCb Ring Imaging Cherenkov (RICH) counters Using a LED light source, we have measured the performance of the MaPMTs as a function of the applied high voltage. Different dynode resistor chains have been used to study the tubes at low gains. The focusing of the photo electrons onto the first dynode and the light collection efficiency of the sensitive area of the MaPMTs have been studied with light scans. Photo electrons converted at the first dynode have been observed. We have also measured the behaviour of the MaPMT in magnetic fields In addition, we present result from data taken with an array of 3x3 MaPMTs mounted onto the RICH 1 prototype vessel, exposed to charged particle beams at CERN, and read out at LHC speed (40 MHz) with APVm chips. Cherenkov light can be detected over the full area of the closely packed MaPMTs by means of quartz lenses focusing the light onto the sensitive area of the device. The number of observed photons is in agreement with the expectations.