Jodie C. Gillespie

Engineering Tool for Temperature, Electric Field and Dose Rate Dependence of High Resistivity Spacecraft Materials

An engineering tool has been developed to predict the equilibrium conductivity of common spacecraft insulating materials as a function of electric field, temperature, and adsorbed dose rate based on parameterized, analytic functions derived from physics-based theories. The USU Resistivity Calculator Engineering Tool calculates the total conductivity as the sum of three independent conductivity mechanisms: a thermally activated hopping conductivity, a variable range hopping conductivity, and a radiation induced conductivity using a total of nine independent fitting parameters determined from fits to an extensive data set taken by the Utah State University Materials Physics Group. It also provides a fit for the temperature dependence of the electrostatic breakdown field strength, in terms of a tenth independent fitting parameter related to an interchain bond strength. The extent of F, T and measured in the experiments were designed to cover as much of the ranges typically encountered in space environments as possible. This Mathcad worksheet calculates the total conductivity and the individual contributions from each conductivity mechanism based on user inputs for F, T and D. It also plots 2D and 3D graphs of the conductivities over the appropriate full ranges of F, T and .

Temperature Dependence of Radiation Induced Conductivity in Insulators

This study measures Radiation Induced Conductivity (RIC) of Low Density Polyethylene (LDPE) over temperatures ranging from ∼110 K to ∼350 K. RIC occurs when incident ionizing radiation deposits energy and excites electrons into the conduction band of insulators. Conductivity was measured when a voltage was applied across vacuum‐baked, thin film LDPE polymer samples in a parallel plate geometry. RIC was calculated as the difference in sample conductivity under no incident radiation and under an incident ∼4 MeV electron beam at low incident fluxes of 10−4–10−1 Gr/sec. The steady‐state RIC was found to agree well with the standard power law relation, σRIC = kRIC⋅DΔ between conductivity, σ and adsorbed dose rate, D. Both the proportionality constant, kRIC, and the power, δ, were found to be temperature dependant above ∼250 K, with behavior consistent with photoconductivity models developed for localized trap states in disordered semiconductors. Below ∼250 K, kRIC and Δ exhibited little change. The observed ...