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The Jiangmen Underground Neutrino Observatory (JUNO) in China aiming to determine the neutrino mass hierarchy is under construction and the 15,000 MCP-PMTs produced in NNVT, which will be installed as the central liquid scintillator detector of JUNO, have been completed and delivered by August of 2020. During the mass production process, breakthrough of the photocathode technology greatly improved the quantum efficiency (QE) of the MCP-PMT from 30% to 35% and so the detection efficiency (DE) has been improved. The performance of other parameters keeps steady during the mass production process of 15,000 MCP-PMTs. The average QE at 400 nm for the 15,000 pieces of MCP-PMTs is 32%. With a layer of high-SEY material deposited on the MCP, the collection efficiency can reach nearly 100% and the average DE at 400 nm for the 15k pieces of MCP-PMTs is 31.5%.

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.

Researchers at IHEP have conceived a new concept of MCP-PMT several years ago. The small MCP units replace the bulky Dynode chain in the large PMTs. In addition the transmission and reflection photocathode are applied in the same glass bulb to enhance the efficiency of photoelectron conversion. After several years R&D, the 20 inch MCP-PMT was successfully produced for JUNO. From 2017 to 2020, all the 20-inch PMTs for JUNO have been under production and testing in NNVT. Furthermore, the QE of this type of MCP-PMT is improved from 28% to 34%@400nm in 2018, and this new technology has already been used on the PMT mass production. The after-pulse rate of this type of the HQE-MCP-PMT was also evaluated at gain ~1.0×107 in this manuscript.

For the next generation neutrino experiment, the MCP-PMT collaboration group has done a lot of work in China. After years of hard work, we have developed 20" MCP-PMT. The MCP-PMT has large sensitive area, high quantum efficiency, high gain and large P/V value for good photon counting performance. The high detection efficiency of 20" MCP-PMT will be used in neutrino detection, and we have got an order for 75% of the PMTs required for neutrino detection. To this end, the MCP-PMT collaboration group also completed the mass production line and batch test system in Nanjing. This presentation will introduce the improvement of 20" MCP-PMT for neutrino detection.

The 20-inch MCP-PMT employs microchannel plates (MCP) as the electron multiplier unlike the traditional photomultiplier tubes (PMTs) with the dynode structure. According to the performance requirements for 20-inch PMTs to be used in the Hyper-Kamiokande (Hyper-K) project, North Night Vision Technology Co., Ltd. (NNVT) developed a novel 20-inch MCP-PMT based on the modification of the 20-inch MCP-PMT used for the Jiangmen Underground Neutrino Observatory by optimizing the design of the focusing electrode structure, the fabrication of the photocathode, and the other processes. The performance of the new NNVT 20-inch MCP-PMTs was evaluated and compared with respect to time resolution and noise. It was found that the transit time spread of the novel type is lower than 4 ns and the dark count rate is lower than 15 kHz. Compared to the previous model, the novel 20-inch MCP-PMT presents enhanced performance for time resolution and noise that is promising for its use in high-energy physics applications such as neutrino detection.

The 20-inch photomultiplier tube has been extensively applied in neutrino detection, for example, in the Super-K, Daya Bay, and JUNO detectors. In order to achieve a high quantum efficiency, two types of structures, namely variably-doped and uniformly-doped structures, are proposed in this study. It is found that the maximum QE of the variably-doped K-Cs-Sb cathode is about 33%, as compared to the maximum QE of 25% for the uniformly-doped cathode. These high QE bialkali photocathodes of the 20-inch photomultiplier tubes were delivered to JUNO, and the average detection efficiency (410 nm) of 6384 mass-produced PMTs is found to be 30.1%.

Researchers of IHEP have conceived a new concept of MCP-PMT several years ago. Small MCP units replace the bulky Dynode chain in the large PMTs. In addition, transmission and reflection photocathodes are in the same glass bulb to enhance the efficiency of photoelectron conversion. After three years of R&D, a number of 8 inch prototypes were produced in 2013. The 20 inch prototypes followed in 2014 and their performances were improved a lot in 2015. This type of PMT has large sensitive area, high quantum efficiency (QE), and large peak-to-valley (P/V) ratio for good single photoelectron detection. Taking in account the performance and cost of PMT and the radioactivity of PMT glass, JUNO ordered 15000 20-inch MCP-PMT from North Night Vision of Technology CO.(NNVT) in Dec.2015. The MCP-PMT collaboration group finished to build the mass production line in Nanjing, and finished the batch test system in the same place in 2016. From 2017 to 2019, all the 20-inch PMTs are produced and tested individually in NNVT. This paper will focus on the mass production and batch test result of 6000 pieces of MCP-PMT prototypes for JUNO.

针对K2CsSb光电阴极生长过程中可能存在的K3Sb、K2CsSb和Cs3Sb三种化合物，采用基于密度泛函理论的第一性原理计算方法，分别建立这三种锑化物阴极材料的立方结构体模型和（111）表面模型，获得了其电子结构与光学性质.对于体模型，计算得到了能带结构、态密度和光学性质，而对于表面模型，计算得到了功函数、光学性质和表面能.结果表明，三种锑化物阴极在中微子与闪烁体作用辐射能量范围（2.4~3.2 eV）内，K2CsSb体材料的吸收系数和反射率与Cs3Sb、K3Sb体材料相近，而K2CsSb（111）表面的吸收系数和反射率低于其他两种阴极的（111）表面.此外，K3Sb的禁带宽度最小、功函数最大且表面能最大，Cs3Sb的表面能最小，其功函数与K2CsSb相近但禁带宽度比K2CsSb小，而K2CsSb禁带宽度最大，功函数和表面能都较小，因此K2CsSb阴极在蓝紫光波段适合作为一种稳定高效的光电发射材料.