Collisionless electrostatic particle-in-cell simulation of rapid target charging along an unbiased dielectric surface due to hypervelocity impact plasmas

Rapid target charging is a phenomenon that has been experimentally observed in hypervelocity impact (HVI) plasmas but has been seldom modeled. In this work, we implement a 2D electrostatic particle-in-cell model to study voltage changes across the unbiased surface of an impacted dielectric material — namely, iron projectiles impacting SiO₂, a novel configuration. We analyze both femtogram and picogram sized particles, of speeds 5 km/s and 15 km/s. Results of surface potential within the impact crater for the femtogram case demonstrate the presence of a minimal decrease in voltage before a rapid positive charging followed by rapid discharge as the surface potential descends towards 0 V. In the picogram case, we found more nuanced behavior, with a more notable rapid decrease in voltage followed by a rapid increase in voltage before subsequent discharge towards 0 V. All cases occurred within fractions of a nanosecond and show a correlation between impactor velocity and voltage magnitude, with peak voltage around 4500 V for the most extreme case. These outcomes, though occurring on a faster timescale, display similar trends to previous experimental results of aluminum-on-tungsten and aluminum-on-aluminum HVIs. The discrepancy in orders of magnitude in the discharging time indicates further investigation is required to determine the relevant physics that are missing from the presented model or possible weaknesses in the original experiments conducted.