Hybrid Photon Detectors and Ion Feedback

The long-term development of the Ion Feedback rate of Hybrid Photon Detectors in the LHCb Ring Imaging Cherenkov detectors was studied as a sensitive measure of the vacuum quality. From a phenomenological understanding of the development reliable predictions can be made for individual photon detectors. Eighty percent of them will operate well for the lifetime of LHCb. In a 20% subsample a faster-than-expected degradation of the vacuum quality was found. A HPD repair and replacement programme guarantees a good performance of the LHCb RICH detector at all time during data taking.