Numerical simulation of secondary electron emission charging at insulator surfaces

The charging process of insulator surfaces in vacuum at high voltages due to secondary electron emission has been calculated using the numerical simulation package SELOP. The systems considered consist of two electrodes at a high-voltage difference, separated by a glass plate or a hollow glass channel. The simulations give insight into the critical high-voltage positions and into the influence of the geometry, the initial voltage distribution and the material properties on the charging profiles and the leakage current paths. A high-voltage quality increase of these systems can be obtained by decreasing the number of impacts of free electrons, adding a coating at all insulating surfaces which has a high value of E-I (i.e. the first crossover point of the secondary electron yield curve) and/or is weakly conductive, and breaking up the total voltage difference in smaller parts by adding electrodes to all surfaces at intermediate voltages.