Plasma Bubble Expansion Model of the Flash-Over Current Collection on a Solar Array-Comparison to EMAGS3 Results

This paper describes the results analysis obtained during the experimental campaign conducted in the frame of the ESA EMAGS3 project “Flash-over (FO) evaluation on large solar panels.” A numerical model has been developed in order to better understand the characteristics of the so-called FO phenomenon. The experimental results, presented in detail in a companion paper, are analyzed in correlation with the present FO model. A basic model based on the assumption of a plasma bubble expansion in vacuum has been developed to model the FO propagation. The model holds on a two-dimensional Cartesian mesh representing the surface of the solar panel. On this mesh, the electrical potential evolution and the current collection are computed supposing that the bubble velocity is constant, the current extracted from the plasma bubble is space-charge limited, the secondary emission is the only source of electrons from the cover-glasses and its potential evolution is only due to the current collection. The inputs of the model are the potential topology before the ESD, the ESD triggering position, and the solar array characteristics (dimensions and cover-glasses capacitance). The outputs of the model are the time evolution of the total FO current, the potential map, and the current collection map on the solar array. The results comparison between the model and the experiments shows a very good agreement in the cases where the potential topology before the ESD is well known. It is especially true when using IPG by plasma because the potential profile is relatively uniform. In that case the comparison with numerical results is concluding. In the case of IPG by electron guns, the potential map before the ESD is relatively hard to obtain. In this case, the agreement between the model and the experimental result is obtained only for a limited number of cases. The detailed comparison between model results and experimental data is shown and analyzed in this paper. It appear- clearly that the plasma bubble extends at the acoustic velocity of the ions generated at the cathode spot level. As a result, ESDs generated on solar cells junction or interconnects do not have the same dynamics.