I. Introduction
The posistive and negative corona discharges are specified by the existence of an ion drift zone which can considred as an impedance in series with the ionization zone and gives to discharges their stability [1] –[3]. In the negative discharge, the positive ions created by ionization can return quickly to the cathode, while the negative ions created by attachment of electrons migrate in the drift zone. In the case of a positive discharge, positive ions are created in the ionization zone and then migrate in the inter-electrode space.