Analysis of tail phenomena in micro-channel plate PMTs

Abstract Photomultiplier Tubes (PMTs) employing micro-channel plate (MCP) are a type of light-detection device designed for weak-light conditions. The MCP multiplication structure has advantage over traditional dynode structures due to its superior temporal resolution and immunity to magnetic interference. The application of atomic layer deposition (ALD) technology has significantly enhanced the longevity of MCP-PMTs. Additionally, the collection efficiency (CE) of MCP-PMTs is increased by coating the upper surface with high secondary-electron emission materials. However, tails on charge and transit time distribution are also observed which deteriorate the charge and time resolution of the MCP-PMT. This can be explained by the existance of the pre-multiplication events and elastically recoiled events. In this paper, the waveforms for four types of MCP-PMTs are analyzed, including the 20-inch MCP-PMT for JUNO, the 20-inch lotus-like MCP-PMT for LHAASO, the 2-inch 8×8-anodes MCP-PMT and the 1-inch single-anode MCP-PMT. Under single-photon detection environment, the full width at tenth maximum (FWTM) is found to be an efficient parameter to realize the distinction of the tails from the normal events for the 20-inch MCP-PMT. For the small-sized FPMT, the origins for the tails in TT distribution is also analyzed.