ESD Propagation Dynamics on a Radially Symmetric Coupon

An increasing body of research has been dedicated to determining the magnitude and scaling of spurious electrostatic discharge current transients on solar arrays and other spacecraft dielectrics under inverted gradient charging conditions. A flashover propagation velocity is typically determined, and assumed to be a single constant number that characterizes the collection of events. The complexity of flight-like test articles and diversity of methods used for deriving this velocity from laboratory data have led to apparently conflicting results. In this paper, we attempt to clarify the radial dynamics of electrostatic discharge (ESD) plasmas on a positively charged surface via the use of a simple test article, composed of eight concentric annular electrodes covered with Kapton. Time-resolved induced ESD currents, recorded as a function of electrode radial distance from the inception point, were used to derive empirical velocity distributions. These distributions lead to a number of effects, such as $\sim 1/r^{2}$ scaling with distance at the beginning of a discharge. Implications for ESD propagation and comparison with previous studies are discussed.