Temperature Dependence of Space Charge Retention in Bulk Acrylic

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.