Dynamics of Fast Electrical Breakdown in Electron-Charged Polymethyl Methacrylate

Abstract

Dielectric materials in charged particle radiation environments have the tendency to trap and store the incident charges within their bulk, generating an electrostatic field inside the material. If the internal electric field increases beyond a given threshold due to continued charge accumulation or the introduction of a field-distorting defect, fast breakdown will occur. During the fast breakdown event, plasma channels rapidly form and grow throughout the solid insulation, redistributing the internal charge and causing permanent damage to the dielectric material. The remnants of the fast breakdown channels are known as electrical trees or Lichtenberg figures, which have long fascinated scientists and artists alike due to their spontaneous, rapid formation and the beauty of the patterns left behind. This dissertation investigates the dynamics of the plasma channel growth including both direct and indirect measurements of the channel propagation inside electron-charged polymethyl methacrylate. Direct measurements include high-speed optical imaging at a gigahertz frame rate to observe the self-luminous channel growth during fast breakdown and measure its velocity over time. Through the high-speed imaging of the breakdown phenomena, a distinct new mode of fast breakdown was observed and analyzed. Indirect measurements of the channel propagation dynamics of this novel breakdown mode as well as other observed modes of dielectric breakdown were achieved by measuring the current produced due to the charge redistribution during the fast breakdown event. The sample geometry and internal charge density were varied in each experiment to determine how these parameters influence the breakdown dynamics, including how the orientation of the breakdown propagation relative to the uniformity of the electrostatic field influences the channel development. The indirect measurements of the breakdown dynamics were directly compared to and validated by the direct high-speed imaging measurements. The experimental results are placed in the context of gaseous discharges in extreme density and pressure conditions, providing a possible explanation for the unusual dynamics observed in electron-charged solid materials.