Studies of the Gain of Small-Pore Size Microchannel Plate Photomultipliers in High Magnetic Fields*

Microchannel plate photomultipliers (MCP PMTs) are small devices that convert light into an electric signal. These devices have many applications, but most notably in physics they are used to readout Cherenkov detectors. In the current designs of the central detector of a future Electron Ion Collider MCP PMTs will readout several Cherenkov detectors located in a magnetic field. Because of this, tests need to be conducted to determine whether the photomultipliers can retain their functionality in the magnetic field of the detector, which can go as high as 3 T. In this work we study two MCP PMTs, with pore sizes of 6 µm and 10 µm, inside a variable magnetic field. We determined that the gain of both devices would slightly increase as the magnetic field increased, until about 0.8T and 0.3T, respectively. While the gain would decrease afterwards, the photomultipliers are able to produce a signal until about 2 T. The orientation of the devices also has an effect, as the gain decreases faster for some orientations. This effect was more noticeable when the magnetic field was above 1 T. Our results suggest that photomultipliers with a small pore size are a viable option to use in the upcoming Collider in a limited range of magnetic-field magnitude.