Acceptance testing of all 20-inch photomultiplier tubes (PMTs) for the JUNO experiment was completed as of Jan. 14, 2021, including 15,000 micro-channel plate (MCP) PMTs developed jointly by IHEP and North Night Vision Technology Co. Ltd (NNVT) and 5,000 dynode PMTs from Hamamatsu Photonics. The average photon detection efficiency (PDE) of all the PMTs is 28.7% and of all MCP PMTs is 28.9%, which is higher than the JUNO requirement of 27%.

The acceptance testing was done at the PMT testing and potting facility, which is located in Zhongshan City, Guangdong Province. The testing process included visual inspection, evaluation of detection efficiency and dark noise, and other measurements.

The facility was jointly established by IHEP and Sun Yat-sen University (SYSU). The container-based test equipment was contributed by Hamburg University and Göttingen University, Germany, and the scanning test equipment was contributed by the Joint Institute of Nuclear Research, Russia. Pan-Asia Electronics Company provided the warehouse and logistics. The acceptance test for the PMTs was jointly undertaken by the JUNO collaborators. Construction of the testing facility was finished in June 2017. Later, the first test equipment arrived and the test procedure was developed. Afterwards, testing began.

The entire testing process took 3-1/2 years and required great efforts from the collaborators, who faced many difficulties such as spending a lot of time away from home institute and working during the Covid-19 pandemic. Nevertheless, the testing was successfully completed.

The remaining work at the facility will be PMT potting and related testing after potting. Those tasks are scheduled to be finished in mid-2021.