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The Status of the R&D of the 20 inch MCP-PMT in China
The JUNO (Jiangmen Underground Neutrino Observatory) to be built in JiangMen, Guangdong province in south China is a generic underground national lab for neutrino physics and other research fields. Its neutrino program requires a high perfor-mance large detector, which needs approximately 16,000 Photomultiplier Tubes (PMTs), that have large sensitive area, high quantum efficiency, high gain and large peak-to-valley ratio (P/V) for good single photoelectron detection. Researchers at IHEP, Beijing have conceived a new concept of MCP-PMT several years ago. The small MCP (Microchannel Plate) units replace the bulky Dynode chain in the tranditional large PMTs. In addition transmission photocathode on the front hemisphere and reflection photocathode on the rare hemisphere are fabricated in the same glass bulb to form nearly 4π effective photocathode in order to enhance the efficiency of photoelectron conversion. A number of experienced researchers and engi-neers in research institutes and companies related to PMT fabrication in China jointly worked on the large area MCP-PMT project. After three years R&D, a number of 8 inch prototypes were produced and their performance was carefully tested at IHEP in 2013 by using the MCP-PMT evaluation system built at IHEP. The 20 inch prototypes were fol-lowed in 2014, and its’ per-formance were improving a lot in 2015. The characteristics of the transmission photo-cathode (Trans. PC) was carefully studied by meas-uring the I-V curves, the quantum efficiency (QE) vs. wavelength, and by mapping the QE for both the 8 and 20 inch photocathodes. Charge spectra of sin-gle photoelectrons, timing properties of anode sig-nals and anode linearity were measured. Noise characteristics and after pulse properties were stud-ied at gain ~1.0×107. We are continuing simulation and experimental work to further improve our 8 and 20 inch MCP-PMT prototypes, in particular to improve the QE of the transmission photocathode and the photoelec-tron collection efficiency (CE) of the MCP unit. We believe for 20 inch prototypes, QE greater than 30% and CE better than 90% CE is possible. With the large area about the photocathode, the QE and DE will be improved, but the TTS and dark noise will be worse. So, the users need to get the balance between these above parameters for differ-ent physics aims. Especially, the glass used for 20 inch MCP-PMT has extra low potassium, low uranium and the con-tents resulting extra low radiation background. The PMT purchase of JUNO The JUNO Bidding started on Oct.23th 2015, and completed on Nov.17th 2015. Compensating the PMT performance with fiducially volume con-vert all specifications to cost, radioactivity, dark noise, TTS, the JUNO ordered 15000 pic 20 inch MCP-PMT from the NNVT.