Comparison of Numerical and Experimental Investigations on the ESD Onset in the Inverted Potential Gradient Situation in GEO

The physical mechanisms leading to the onset of primary electrostatic discharges (ESDs) are investigated. The breakdown voltages obtained in numerical simulation are compared to experimental evidences. The inception voltage of an ESD, i.e., the minimum breakdown voltage, is estimated experimentally using an innovative method to create the inverted potential gradient (IPG) situation. An ultraviolet source has been set in the CEDRE chamber of the Office National d'Etudes et Recherches Aérospatiales to reproduce the IPG situation by photoemission (as in flight). This method has permitted us to determine with a good precision the differential voltage leading to ESDs in various configurations. The SPIS-ESD tool has been developed to simulate the differential changing phase, the 3-D electron avalanche, and the ESD triggering (at a mesoscopic scale) in IPG situation. This tool is able to reproduce the same geometry as in the experimental setup. The results from this tool have been compared to the experimental evidences for different configurations. The influence of the geometry of the triple point and the dielectric material on the ESD inception voltage has been tested. The ESD inception voltage fails to be quantitatively predicted due to uncertainty on the surface state and on the value of the dielectric edge conductivity. Nevertheless, a qualitative agreement is obtained between the experimental and numerical results concerning the variation of the ESD inception voltage as a function of the triple point geometry (irradiation angle and conductor width).