Lifetime-Extended MCP-PMT

TL;DR

This paper investigates the degradation mechanisms of MCP-PMTs with multialkali photocathodes and introduces countermeasures to extend their lifetime while maintaining key performance metrics.

Contribution

It identifies neutral residual gases as a cause of QE degradation and presents new MCP-PMT designs with improved longevity and stable performance.

Findings

QE stable up to 2-3 C/cm^2 charge accumulation

Maintains ~40 ps time resolution and 60% collection efficiency

Dark counts remain low at 20-300 Hz

Abstract

In order to develop a long-lifetime MCP-PMT under high rates of circumstance, we investigated the degradation of the quantum efficiency (QE) of PMT's 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-PMT's with 4 or 4x4 multi-anodes. The performances of the PMT's were measured: QE was stable up to an integrated amount of anode output charge of 2-3 C/cm^2, while keeping other basic performances steady, such as the time resolution for single photons of ~40 ps, a photoelectron collection efficiency (CE) of 60%, a multiplication gain (G) of a few x 10^6, and dark counts of 20-300 Hz. The causes of QE degradation are discussed.