Study and removal of the flash from the HV divider of the 20-inch PMT for JUNO

Many neutrino experiments with PMT system have been suffered from the unexpected flash, which is a corona discharge generated by the HV divider of PMT. There are approximately 20,000 20-inch PMTs and HV dividers in JUNO, hence it is critical for minimizing the flash for this large PMT system in order not to contaminate the physics data coming from neutrinos. In this paper, we studied the characteristics of the flash and measured its emission rate. Eventually the sources of the flash were identified, and the solutions were found in reducing and completely removing the flash.