Characterization of Electrostatic Discharge Currents in Electron-Charged Polymethyl Methacrylate as a Proxy for Natural Compact Intracloud Discharges

Electrostatic discharges occur in numerous media on a range of length scales, from microscopic discharges inside electronic materials to kilometer-long channels in air during natural lightning events. To study the mechanisms and behavior of electrostatic discharges inside materials, we measured the discharge currents produced during dielectric breakdown of electron-charged polymethyl methacrylate. The resulting current waveforms were analyzed and the relevant parameters for characterizing the waveform morphology were extracted and investigated to build a functional model to describe and characterize the waveforms from these types of discharges. The model involves a distinction between one-dimensional and two-dimensional discharge channel growth, which are governed by separate principles and thus have different contributions to the total measured discharge current. We show that this model, which is derived from the discharge channel growth during the event, allows us to infer characteristics about the dynamics of the breakdown, such as the instantaneous velocity of the channels during breakdown. We applied this model to the context of natural compact intracloud discharges, or narrow bipolar events, by scaling the one-dimensional waveforms in size and time to those relevant to compact intracloud discharges. We find that the discharge currents derived from centimeter-scale and submicrosecond-duration electrostatic discharge events in electron-irradiated polymethyl methacrylate obey the same functional form of those of natural compact intracloud discharges, leading to the conclusion that the polymethyl methacrylate– (PMMA) based discharges may a useful laboratory tool to reproduce narrow bipolar events discharge currents. We calculated the electric field that would be radiated by these scaled discharge currents using published measurement parameters for compact intracloud discharges and found that the magnitude and pulse shape agree with observations very well. In addition, we find that energy spectral density of the scaled PMMA discharge waveforms have a similar frequency dependence in the 3- to 300-MHz band to those of compact intracloud discharges. These results support the idea that space charge in and around thunderclouds may be the driving mechanism of compact intracloud discharges and that electron-irradiated solid dielectrics may be a useful laboratory-based analog to study natural lightning events.