In operation with a magnetic shield in close proximity there will be corona discharges unless the bare HPD electrode and the shield are properly insulated.
Development of a Hybrid Photo-Diode and its Front-End Electronics for the BTEV Experiment
Several other factors may facilitate its ignition, such as highly ionizing particles, sparks, sharp points on electrodes causing corona discharges, or thin anode wires .
Summary and Outlook of the International Workshop on Aging Phenomena in Gaseous Detectors (DESY, Hamburg, October, 2001)
This approach was already used in the case of streamer corona discharge dynamics [28, 29] and for analysis of ionization wave dynamics in low-temperature plasma jets .
High order fluid model for streamer discharges. II. Numerical solution and investigation of planar fronts