Speaker
Description
Large Area Picosecond Photon Detectors (LAPPDs) and High Rate Picosecond Photon Detectors (HRPPDs) are large area Micro-Channel Plate-PMTs (MCP-PMTs) resulting from a long-lasting collaboration between academy and industry. The atomic layer deposition technique that improves the MCP-PMT lifetime has been introduced within this development. These photosensors have a very good time resolution typical for MCP-PMTs, down to 15-20 ps for single photon detection. They have high Quantum Efficiency (QE) with peak values larger than 30% and low Dark Count Rates ($\sim$few kHz/cm$^{2}$). A distinguishing feature of LAPPDs and HRPPDs is a large sensitive area of about 20$\times$20 cm$^{2}$ and 10$\times$10 cm$^{2}$, respectively. HRPPDs have fine granularity with 3.25$\times$3.25 mm$^{2}$ anode pads DC coupled to external readout electrodes. In the case of HRPPDs, the two MCP stages have 10 $\mu$m diameter capillaries and can provide a gain above 10$^{7}$ at a bias voltage not larger than 800 V across each of them. HRPPDs are the baseline photosensor of a proximity focusing RICH (pfRICH) of the Electron-Proton/Ion Collider (ePIC) experiment at Elecron Ion Collider (EIC). They are also considered for a high performance DIRC (hpDIRC) of the same experiment.
In this contribution, we first present the timing resolution of an LAPPD photosensor detecting Cherenkov light produced in a quartz radiator at a CERN PS hadron test beam performed in 2022. Results show a Single Photo-Electron (SPE) time resolution of 87 ps rms. We then present the performance of an LAPPD in a magnetic field up to $\sim$1.5 T. The measurements were performed at CERN using MNP-17 and M113 vertical dipole magnets in 2023 and 2024, respectively. Exponential gain drop as a function of a magnetic field strength, with a rather moderate dependence on the field line orientation with respect to the photosensor window normal direction has been observed. The relative Photon Detection Efficiency (PDE) in the magnetic field is also affected. However, both the gain and the efficiency can be partially recovered by increasing the bias voltages across the two MCPs. We also present the results of aging studies performed with an HRPPD photosensor in 2025. The strategy of these measurements is to expose a small area of the photocathode to substantial light illumination and monitor a degradation of the effective PDE as a function of the integrated photon flux as well as the charge generated in the electron multiplication process. The aging effect on the gain will also be reported. All these studies are performed by the INFN Genova and INFN Trieste groups.
