Long term aging test of the new PMTs for the HL-LHC ATLAS hadron calorimeter upgrade

The central hadronic Tile calorimeter (TileCal) of the ATLAS experiment, is read out by approximately 10,000 photomultipliers (PMT). Earlier PMT performance test results have shown a degradation in response due to the integrated anode charge, with projected losses exceeding 25% for approximately 8% of the photomultipliers, corresponding to the most-exposed TileCal cells, which are expected to integrate charges up to 600 C over the High-Luminosity Large Hadron Collider program. To maintain performance, these photomultipliers will be substituted with a newer version. A local test bench In the Pisa laboratory is being used to study the performance of the new photomultipliers after integration of anode charges exceeding 300 C. The new photomultiplier model has been tested for the first time after integrating more than 100 C of anode charge. Preliminary results obtained in the Pisa laboratory are shown.