Dynamic gain optimization for large-area PMTs for OSIRIS

Photomultiplier-Tubes are photodetectors with good single photon resolution. For the optimal photon reconstruction the PMT gain is required to 1E7 e- per electron. The gain of the PMT depends exponentially on the applied high voltage. By regulating the high voltage, the gain can be tuned and stabilized. By using the presented technique it is possible to simply connect all PMTs to the readout system, without characterizing the gain and the correct HV beforehand. By using the charge of dark counts there is no need for a special light source in the detector for implementing this procedure. Potential changes of the PMT gain can be compensated during runtime. This concept will be implemented and tested in the OSIRIS detector.