Lifetime of microchannel-plate photomultipliers for the PANDA-DIRC

At the PANDA experiment of the new FAIR-facility at GSI (Darmstadt) particle identification will be achieved by using DIRC-detectors (Detection of Internally Reflected Cherenkov Light). The photons of the Cherenkov cone are guided to the photosensors inside the radiator by total reflection. With the planned optics at the barrel-DIRC a spatial resolution of about 5mm is necessary for the reconstruction of the Cherenkov cone. This implies photon rates of about 1(MHz)/(cm2) at the sensor surface. To correct dispersive effects in the radiator, a time resolution of at least 100 ps should be achieved. Possible sensor candidates are microchannel-plate photomultipliers (MCP-PMTs), if a satisfactory lifetime can be obtained. With reaction rates of 20 MHz and a PANDA lifetime of about 10 years, an integrated charge of several (C)/(cm2) will be collected at the MCP anode. The lifetime behaviour of a few types of MCP-PMTs is currently under investigation in Erlangen.