Temperature Dependence of Space Charge Retention in Bulk Acrylic

ABSTRACT

Charge loaded dielectrics (CLDs) are created when a dielectric is exposed to high‐energy charged particle radiation and accumulates an internal space charge. The material behavior of CLDs is not as well understood as that of non‐irradiated dielectrics. Specifically, two characteristic processes remain under investigated: ( i ) the slow, quasistatic charge dissipation (minutes to hours timescale) and ( ii ) the spontaneous dielectric breakdown event (sub‐microsecond timescale). Herein the temperature dependence of space charge retention in electron‐irradiated bulk acrylic is probed by thermally manipulating charge carrier mobility over a temperature range of –80°C ≤ T ≤ 0°C. Charge carrier mobility in bulk acrylic, proportional to charge dissipation, was able to be restricted indefinitely when bulk samples were stored below a critical temperature found to be in the range of –50°C ≤ T ≤ –40°C. Above this critical temperature, the amount of transferred charge measured during each breakdown decreased exponentially. A similar temperature‐dependence in the electrical treeing pattern morphology is observed post dielectric breakdown as direct physical evidence of the plasma created during breakdown. These observed temperature‐dependencies suggest space‐charge mobility in electron‐irradiated bulk acrylic is dominantly phonon‐dependent and strongly influenced by the β‐relaxation temperature of acrylic, which falls within the –50°C ≤ T ≤ –40°C critical temperature range.