Performance of Planacon MCP-PMT photosensors under extreme working conditions

The performance of the 25 μm-pore Planacon MCP-PMT is discussed here and the device is evaluated for the use as the main photosensor of the Cherenkov arrays of the Fast Interaction Trigger (FIT) detector for the upgrade of the ALICE apparatus at the CERN LHC. During the LHC Run 3 and 4 FIT has to operate in strong magnetic fields and in large particle fluxes without significant ageing effects. The expected dynamic range for central modules of Cherenkov arrays of FIT is from 1 to ∼ 1000 MIPs. The required single-MIP time resolution is below 50 ps and the expected average repetition rate is 50 kHz. To fulfil these requests, the Planacon XP85012/A1-Q MCP-PMT has been customized into the XP85002/FIT-Q version. With the modified Planacon we were able to achieve a time resolution as low as 13 ps and ensure good timing of the device under the required dynamic range. A description of the implemented MCP-PMT modifications is presented here together with the outcome of the in-beam test of the assembled Cherenkov module and dedicated ageing- and magnetic field tests.