Performance Evaluation of Microchannel Plates Photomultiplier Tubes with an Active Ion Barrier

Micro Channel Plate (MCP) Photomultiplier Tubes (MCP-PMTs) are photodetectors with single photon sensitivity, high timing resolution (30-40 ps), and can produce a very large gain (10⁶) across the pair of MCPs. Furthermore, they have many benefits such as their ability to work in strong magnetic fields due to their compact structure. However, MCP-PMTs have known to deteriorate quickly due to liberated positive ions from the MCP damaging the photocathode. In the process, the quantum efficiency along with the gain of the tube can be adversely affected. Many methods have been developed to prolong MCP-PMTs lifespans including active and passive ion barriers. Here, we test the performance of novel MCP-PMTs with an active ion barrier grid that redirects the liberated positive ions toward the MCP using an opposing electric field. We demonstrate that the ion feedback rate varies inversely with the applied potential on the grid. Furthermore, our experiments show that critical parameters such as the timing resolution, gain and pulse height distributions are not adversely impacted by the applied potential on the active ion barrier. These observations, the first of their kind, provide essential data necessary to design new MCP-PMTs geometries with prolonged lifespans.