Modification of ion flow field by insulator surface with rod-plane geometry in SF6

The effect of an insulator inserted along the axis of a rod-to-plane gap on an ion flow field in SF₆ gas is investigated experimentally in the pressure region where a preceding corona discharge exists. Without the insulator, the calculated electric field on the plane electrode agrees fairly well with the measured one. The high density space charge near the rod electrode produces the corona stabilization effect. With the insulator, the accumulated charges on the insulator affect the current and electric field distribution on the plane electrode which are variable with pressure, while the normalized charge density near the plane electrode is less dependent on pressure. These characteristics may be attributed to the change in the electric field distribution by the accumulated charge, the increase in the ratio of the dielectric strength in gas gap to that along the insulator surface with the gas pressure, and the thermal diffusion of ions near the insulator. On the basis of measured results, the ion flow field in the presence of the insulator is discussed