A container-based facility for testing 20'000 20-inch PMTs for JUNO

Abstract

The main goal of the JUNO experiment is the determination of the neutrino mass ordering. To achieve this, an extraordinary energy resolution of at least 3 % at 1 MeV is required for which all parts of the JUNO detector need to meet certain quality criteria. This is relevant in particular for those which are related to the energy resolution of the detector, such as the photomultiplier tubes (PMTs) to be deployed in JUNO. This paper presents the setup and performance of a dedicated PMT mass testing facility to examine and characterize the performance of the 20-inch JUNO PMTs. Its quasi-industrial size and operation level allows to test all 20000 PMTs intended to be used in the JUNO experiment. With this PMT mass testing system, several key characteristics like dark count rate, peak-to-valley ratio, photon detection efficiency, and timing resolution have been determined at an operating gain of 1 × 107 and assessed with respect to the requirements of JUNO. Measurement conditions and modes for the PMTs as well as estimated accuracies for the determination of the individual PMT parameters with the system are presented as well.

Mass Testing and Characterization of 20-inch PMTs for JUNO

“…3 with G the measured gain, which is consistent with the applied fitting function used for dynode PMTs in the selected range [28]. Additional information about the HV determination can be found in [68]. A discussion about different methods for the gain determination and their effects can be found also in separate papers [24,81,82].…”

“…The containers achieve a stable performance over time as well as a sufficient accuracy of e.g. ≤ 1 % for the absolute PDE and ≤ 1 ns for the timing parameters such as the TTS (only container #B) [68] -this will be discussed also in secs.4.4 and 4.6. Hence, the system can provide reliable and comparable results for all available 20-inch PMTs characterized in this PMT testing campaign.…”

“…The main setup of the individual (acceptance) tests of all 20,000 20-inch JUNO PMTs is the so-called container system. This system has been described extensively in a stand-alone paper [68], where all details about mechanical setup, data taking electronics, measurement process and accuracies can be found. To enhance understanding of the later presented results from the PMT mass testing, the setup will be briefly described here as well.…”

“…Hence, the system can provide reliable and comparable results for all available 20-inch PMTs characterized in this PMT testing campaign. More details about this system can be found also in [68,73,74].…”

“…6: Measurement and classification procedure performed by the two testing systems. Details of the full PMT characterization process performed by the container system can be also found in [68].…”