Speaker
Description
The Fast Interaction Trigger (FIT) detector of the ALICE apparatus at LHC includes a Cherenkov subsystem utilizing 52 Planacon XP85002/FIT-Q microchannel plate-based photomultiplier tubes (MCP-PMTs). Operating in the forward rapidity region of ALICE since 2021, these devices sustain radiation load equivalent to ~10^12 1-MeV n_eqv/cm^2 hadron fluence and ~100 kRad total ionizing dose. Moreover, under the most intense flux of Pb-Pb ion collision products, the innermost photosensors detect 3x10^8 photoelectrons per second, resulting in 0.6 μA/cm^2 average anode current. The lifetime-extended version of the Planacon MCP-PMT with atomic layer deposition (ALD) cannot handle such a large anode current. Non-ALD MCP-PMTs are therefore used in ALICE FIT. Ageing trends exceeding 1.5 C/cm^2 have been collected to monitor changes in MCP-PMT response, and both the precise timing and counting performance of the Cherenkov detector remain unaffected so far. The detector will stay in operation until the end of LHC Run 4 in 2033.
This talk gives an overview of our experience of operating non-ALD Planacon MCP-PMTs in the harsh environment of the ALICE experiment’s forward region: results of ageing and radiation damage monitoring, the newly observed self-recovery effect of aged photosensors, response variation and anode current saturation in strong magnetic fields.
