About PMTs first series cold and warm tests G. Raselli (INFN and Universita di Pavia) F. Tortorici (INFN and Universita di Catania) M. Rossella (INFN and Universita di Pavia) A. Falcone (INFN and Universita di Pavia) 09/12/2015

Tests on PMTs first series started on Tuesday 1 st December 2015 – 10 % of PMTs of each batch has to be tested at cold temperature: in this case at least 8/80 samples – Since in the large dewar there is enough space for 10 PMTs to be tested in parallel, we selected randomly 10 units – They were provided with a new voltage divider and then tested at warm temperature – Then, they were mounted in the large dewar at building 182 for the tests at cold The cool down in LAr started yesterday (Dec 8, 2015) The test is in progress

28 additional PMTs were provided with the new voltage divider – A quick test has been performed: all of them are correctly functioning – More accurate tests are being carried out These PMTs will NOT be tested at cold temperature, so it is important to verify the stability over at least 24 hours of working with the power supply on Few samples were cleaned and prepared for evaporation; cleaning procedure is under definition (see Maura Spanu’s presentation) Voltage dividers pre-series (52 units) is now working well and normal production is being authorized A new batch of PMTs is under delivery