Design of the PMT underwater cascade implosion protection system for JUNO

Abstract Photomultiplier tubes (PMTs) are widely used underwater in large-scale neutrino experiments. As a hollow glass spherelike structure, implosion is unavoidable during long-term operation under large water pressure. There possibility of cascade to neighbor PMTs due shockwave. Jiangmen Underground Neutrino Observatory designed protection structure for each 20-inch PMT, consisting top cover, bottom and their connection. This paper introduces the requirement design PMT system, including material selection, investigation manufacture technology, prototyping. Optimization validation by simulation experiments also presented.