Lifetime-extended MCP-PMT

In order to develop a long-lifetime MCP-PMT under high rates of circumstance, we investigated the degradation of the quantum efficiency (QE) of PMTʹs with a multialkali photocathode. We found that not only positive ions, but also neutral residual gases would damage the photocathode resulting in an enhancement of the work function; their countermeasures were established in newly manufactured square-shaped MCP-PMTʹs with 4 or 4 × 4 multi-anodes. The performances of the PMTʹs were measured: QE was stable up to an integrated amount of anode output charge of 2–3 C/cm2, while keeping other basic performances steady, such as the time resolution for single photons ( σ TTS ) of ≃ 40 ps, a photoelectron collection efficiency (CE) of 60%, a multiplication gain (G) of a few ×106, and dark counts of 20–300 Hz. The causes of QE degradation are discussed.