Long Term Aging Test of the New PMTs for the HL-LHC ATLAS Hadron Calorimeter Upgrade

TileCal, the central section of the hadronic calorimeter of the ATLAS experiment, is read out by 9852 photomultipliers. Earlier findings in the photomultiplier performance show a degradation in response due to the integrated anode charge, with projected loss exceeding 25% for 8% of the photomultipliers that will integrate an anode charge of 600 C, expected in the High-Luminosity Large Hadron Collider program. These photomultipliers will be replaced with a newer version. In the Pisa laboratory, a local test bench is being used to study the performance of the new photomultipliers after integration of an anode charge exceeding 200 C. Preliminary results obtained in the Pisa laboratory are shown.