Interpretation of the surface charge decay kinetics on insulators with different neutralization mechanisms

Surface charge decay kinetics on corona-charged polymeric insulators were studied. In the experiment, the sample surface exposed to corona was kept open to ambient air whereas the opposite surface was in contact with a grounded plate. The resulting surface potential distribution was scanned in a raster mode using a Kelvin electrostatic probe, from which the relief map of charge density was obtained by an inverse calculation method. The developed procedure allowed for implementation of two study cases: (i) gas neutralization took place under natural conditions, with enhanced concentration of free ions, and with limited gas volume; (ii) surface charge decay occurred only due to bulk neutralization. Three mechanisms were considered responsible for surface charge decay, i.e., bulk neutralization, gas neutralization, and surface conduction. They were discussed separately with the help of numerical models, which quantified the relative importance of each mechanism on the total process of charge decay. The results of the latter case were further utilized to determine the energy distribution of electron and hole traps of the materials based on the isothermal relaxation current theory.