Afterpulse timing and rate investigation of three different Hamamatsu Photomultiplier Tubes

We present the results of the tests performed on 90 photomultiplier tubes (PMT) to characterize their afterpulses. Three different types of Hamamatsu PMTs (R7525, R6427, and R1398) were studied for their afterpulse rates and timings at different incident light intensities and gain values, at the University of Iowa PMT test station. Afterpulse rates show slight increase with the PMT gain, but there is almost no dependence on incident light intensity. Three specific time delays are determined for the afterpulses, and their individual rate contributions are characterized. The results from manufacturer's independent tests on R7525 PMTs are reported, as well. The possible effects of these afterpulses on the future hadron collider experiments are also discussed.