Distinct Initiation Processes of Vacuum Flashover under Non-Uniform Field: a Multiphase Framework

Vacuum flashover commonly appears over dielectric material, deteriorating reliability and longevity of electrical equipment. We present two distinctive modes where flashover initiates from cathode or anode, with fundamentally different mechanisms and discharge developments. Simulation and theories are provided, corroborated by experimental results of detected optical characteristics. The cathode-initiated flashover (CIF) is due to a multipactor formed over surface which then induces outgassing and a low pressure gas discharge. The anode-initiated flashover (AIF), on the other hand, is triggered by partial leakage near anode triple junction due to strong vertical field, which then fuels the discharge with two ionization zones starting from both junctions to converge. A multiphase framework is given conceptually to combine both CIF and AIF. Their relations with field distribution, beam injection are clarified as well.