Electron Transport Models and Precision Measurements With the Constant Voltage Conductivity Method

Recent advances are described in the techniques, resolution, and sensitivity of the constant voltage conductivity (CVC) method and the understanding of the role of charge injection mechanisms and the evolution of internal charge distributions in associated charge transport theories. These warrant reconsideration of the appropriate range of applicability of this test method to spacecraft charging. We conclude that under many (but not all) common spacecraft charging scenarios, careful CVC tests provide appropriate evaluation of conductivities down to ≈ 10^-22 (Ωcm)^-1, corresponding to decay times of many years. We describe substantial upgrades to an existing CVC chamber, which improved the precision of conductivity measurements by more than an order of magnitude. At room temperature and above and at higher applied voltages, the ultimate instrument conductivity resolution can increase to ≈ 4·10^-22 (Ωcm)^-1, corresponding to decay times of more than a decade. Measurements of the transient conductivity of low-density polyethylene using the CVC method are fit very well by a dynamic model for the conductivity in highly disordered insulating materials over more than eight orders of magnitude in current and more than six orders of magnitude in time. Current resolution of the CVC system approaches fundamental limits in the laboratory environment set by the Johnson thermal noise of the sample resistance and the radiation-induced conductivity from the natural terrestrial background radiation dose from the cosmic ray background.