Gain Studies of Small-Pore-Size MCP PMTs in High Magnetic Fields for the Electron Ion Collider*

At the Thomas Jefferson National Accelerator Facility (JLab), ongoing research supports the detector and accelerator design of the Electron Ion Collider (EIC). At JLab’s High-B facility, various Microchannel-Plate Photomultipliers (MCP PMT) are being studied in a variable magnetic field. An MCP PMT is a compact device, which converts light into an electrical signal, and can be used to readout the EIC Cherenkov detectors. The main EIC detector will have a 3-T central field, and it is critical to understand if MCP PMTs retain their performance at the high fields expected at the various locations of the readout of the Cherenkov detectors. As the magnetic field increases, the gain of the PMTs decreases; but it does so at a smaller rate for smaller pore-size sensors. Here, we present our studies on the gain of a 6- micrometer pore-size Photek sensor—currently the only available multi-anode MCP PMT of this small pore size. We also show results for a 10-micrometer Planacon High-Collection efficiency MCP PMT. For several orientations relative to the field, the smaller pore-size sensor can be operated even at 2 T. The larger pore-size sensor can be operated up to nearly 2 T only at standard orientation. These results suggest that each PMT could be useable in a specific application at EIC.