Document Type

Article

Journal/Book Title/Conference

17th Spacecraft Charging Technology Conference

Location

Avignon, France

Publication Date

6-2024

Abstract

The conductivity of insulating materials can be enhanced above the baseline dark conductivity by incident radiation via inelastic scattering that imparts energy to electrons in trapped states and excites them into the conduction band, without depositing charge. Such radiation-induced conductivity (RIC), caused by ionizing radiation present in harsh space plasma environments, can play a critical role in space charge dissipation within highly insulating materials used in spacecraft. An equilibrium value for RIC, 𝜎RIC, is attained after prolonged exposure to an incident dose rate; this follows a standard theoretical power law model proposed by Rose/Fowler/Vissenberg, 𝜎RIC(T, Ḋ) = kRIC ∙ Ḋ∆, where kRIC(T, Ḋ) and Δ(T, Ḋ) are material parameters dependent on both temperature T and dose rate, Ḋ. RIC behavior of real materials requires a finite amount of time for the measured current to come to equilibrium after radiation is turned on and to return to dark conductivity after radiation is turned off. The time-dependent onset of RIC (characterized by an exponential increase in 𝜎RIC) and of delayed RIC after the dose is terminated (characterized by a hyperbolic inverse time-dependent decay), are controlled by defect energy-dependent time constants for carrier trapping and recombination. The model employed here to fit time-dependent RIC curves for various polymeric materials considers two different time constants for shallow and deep traps, which can themselves be dependent on T and Ḋ. Time-dependent RIC data sets are not common, particularly over ranges of temperature. Data from a large RIC database from Utah State University are analyzed for six polymeric materials—polyether ether ketone (PEEK), polyimide (PI, Kapton HNTM and Kapton ETM), polytetrafluoroethylene (PTFE, TeflonTM), ethylene-tetrafluoroethylene (ETFE, TefzelTM), and low density polyethylene (LDPE)—for ranges of temperatures from ~110 K to ~350 K and dose rates from ~50 μGy/s to ~0.1 Gy/s; the values of kRIC(T, Ḋ) and Δ(T, Ḋ) at equilibrium for these data have been previously investigated. The temperature and dose rate dependence of the parameters of this time-dependent RIC model are determined and compared for the different materials.

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