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Abstract: An accurate study and measurement about the aging effects on two large area photomultipliers (PMT) has been performed for over 3 years. The PMTs were 10in., 10 stages Hamamatsu R7081, one with standard bialkali and the other one with super-bialkali photocathode. The gain, dark count rate, charge and timing properties have been measured, as well as the fraction of the spurious pulses. During the aging cycles, the anode current of the two photo-multipliers has been monitored and recorded in order to measure the total output anode charge and determine the aging grade. The aging conditions have been set by the use of a 400nm LED regulated to about 3 photoelectrons (pe) at about 400kHz. The aging process was stopped when the total charge arrived up to about 2000C for both the PMTs. Measurements of the parameters of the two PMTs have been performed periodically using a 400nm pulsed laser in single photoelectron condition. Considering the main results, only the gain showed a variation while all the other parameters remain quite stable. A first phase of up-drift shows an increase of the gain of about 10% and is followed by a final phase of down drift, which shows a faster diminution of the gain of about 30%. The mechanism of the gain drift has been modeled and compared with the results. [Copyright &y& Elsevier]

The main task of the Top Tracker detector of the neutrino reactor experiment Jiangmen Underground Neutrino Observatory (JUNO) is to reconstruct and extrapolate atmospheric muon tracks down to the central detector. This muon tracker will help to evaluate the contribution of the cosmogenic background to the signal. The Top Tracker is located above JUNO's water Cherenkov Detector and Central Detector, covering about 60% of the surface above them. The JUNO Top Tracker is constituted by the decommissioned OPERA experiment Target Tracker modules. The technology used consists in walls of two planes of plastic scintillator strips, one per transverse direction. Wavelength shifting fibres collect the light signal emitted by the scintillator strips and guide it to both ends where it is read by multianode photomultiplier tubes. Compared to the OPERA Target Tracker, the JUNO Top Tracker uses new electronics able to cope with the high rate produced by the high rock radioactivity compared to the one in Gran Sasso underground laboratory. This paper will present the new electronics and mechanical structure developed for the Top Tracker of JUNO along with its expected performance based on the current detector simulation. [ABSTRACT FROM AUTHOR]