Contribution of microchannel plate luminescence to the noise of 20-inch photomultiplier tubes

Since microchannel plate (MCP) photomultiplier tubes are used mainly to detect weak signals, their utility is greatly affected by their noise. This is true, for example, for the 20-inch MCP photomultiplier tubes used in high-energy physics research. We have built an MCP luminescence test system by coincidence testing method, and have analyzed the sources of such MCP luminescence by contrast test. We find that this MCP luminescence is due to electron multiplication in the photomultiplier tube. In order to analyze the proportion of MCP luminescence noise in an MCP photomultiplier tube, a noise model of the tube is established, including various sources of noise such as thermal electron emission from photocathode, MCP luminescence, MCP noise electron, glass luminescence, and ion feedback. Then we set up a test and evaluation system of MCP luminescence, measuring count-rate variations of 20-inch MCP photomultiplier tubes under incident light with different numbers of photoelectrons per pulse and different pulse rates. Through a series of calculations, the ratio of the noise from the MCP luminescence to the total noise of the 20-inch MCP photomultiplier tubes was determined. The results show that the luminescence noise of the MCP accounts for about 7 to 22% of the noise of the whole tube. Our analytic method can be extended to analyze the main noise sources of other MCP-type photomultiplier tubes, a direction worth pursuing to reduce noise and further improve the overall performance of MCP photomultiplier tubes.