Local Space-Charge Memory and Grounded-Electrode Transient Response in a Needle–Plane Air Gap Under Polarity Reversal

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Polarity reversal changes not only the instantaneous electric field in a needle–plane air gap but also the subsequent field–particle coupling through the charged-particle distribution established before reversal. For a configuration in which the grounded needle and grounded lower plate share the same return path, it remains unclear to what extent this local history-dependent state is transferred to the complete grounded conductor and its externally measurable current. Here, a two-dimensional axisymmetric electrostatic model (ES) and a drift–diffusion–reaction–Poisson–discharge-fluid model (EDIS) were established for a 50 mm needle–plane air gap. Positive-to-negative (P2N)/negative-to-positive (N2P) reversals and history-retained/history-reset (H/R) controls were used to separate the effects of reversal path and pre-existing charged-particle state. Over the tested 0–2τ reset-hold range, the representative near-tip electron density in H remained approximately 15–16% higher than that in the corresponding R case, whereas the H/R conductor-integrated response of the complete common-ground assembly was indistinguishable at the present numerical resolution. Outer-domain analysis further showed that for the representative 15 kV case in the 300 mm reference domain, the EDIS and ES common-ground integrated responses differed by approximately 3.3%. Experimentally, P2N and N2P reversals were repeated at 5, 10, and 15 kV, yielding 120 events. The main common-ground current pulse increased with voltage magnitude and maximum voltage slew rate, and the median event-level Pearson correlation with signed dV/dt was approximately 0.989. Different capacitance-baseline constructions yielded central residual-integral levels of approximately 18–19%; after multiplicity correction, the 15 kV fixed-window absolute integral was the direction-sensitive terminal metric with the strongest statistical support. Under the investigated conditions—a nominal 0.5 mm tip radius, 50 mm gap, approximately 3 ms reversal time, and weak-discharge regime—the reversal path and particle history primarily reorganize the near-tip charged-particle state, whereas the dominant scale of the common-ground transient remains closely associated with the applied-voltage variation and the capacitive response of the system.

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