SPACE CHARGE LIMITED DIELECTRIC BREAKDOWN, OR: HOW I LEARNED TO STOP WORRYING AND LOVE APPROXIMATIONS

Abstract

Space charge induced dielectric breakdown in spacecraft components exposed to energetic cosmogenic radiation has remained poorly understood despite decades of research. In this work, breakdown in electron irradiated polymethyl methacrylate is described by a new 1D space charge limited front (SCLF) model that reconceives breakdown as a propagating front rather than a diffuse event. To quantify embedded charge distributions and validate model predictions of breakdown charge transport, charge distributions produced in bulk PMMA by electron irradiation were mapped using custom designed pulsed electroacoustic systems. These measurements both supported the SCLF model of breakdown charge transport and revealed unexpected positive charge accumulation at high electron deposition within PMMA. To capture the real time dynamics of the breakdown front, high speed direct and streak imaging were employed, and a sharply localized front was observed whose velocity increased with embedded charge density, in agreement with SCLF predictions. To characterize the difficult to probe environment through which the breakdown current is transported, varied resistance loading was used to measure the time dependence of breakdown source impedance. These measurements demonstrated a transition from a capacitive, high impedance regime during front propagation to a resistive, low impedance state after breakdown, thereby highlighting the differing current transport environments at and behind the breakdown front. Limitations of the 1D SCLF arising from multi sign charge configurations, three dimensional effects, and transient breakdown pathways were identified, and the necessity for multidimensional numerical simulations to extend and refine the SCLF framework for spacecraft relevant geometries was outlined. Together, these results establish a unified experimental and theoretical foundation for understanding space charge induced breakdown in PMMA and outline a clear path for future quantitative empirical validation and model development.