Experimental Measurement of Low-Intensity and Long-Duration Internal Charging Behavior

We report initial results from the EU FP7 Spacestorm project on the experimental behavior of commonly-used space dielectric materials in an electron environment where the incident electron current is significantly below safe levels specified by design standards. The realistic electron environment facility (REEF), which uses an intense strontium-90 beta-emitting radioactive source to simulate the space environment, has been recommissioned at the University of Surrey for this purpose. Using a combination of shielding and variable source-sample separation REEF can achieve a very wide dynamic range in electron current, from the very high levels associated with an extreme space weather event, down to the levels below the European Cooperation for Space Standardization low temperature (<;25 °C) safety threshold of 0.02 pA/cm
²
. In order to allow for the accumulation of significant levels of charge at such a low current, these experiments need to be run continuously for several weeks, far in excess of typical experimental investigations of internal charging phenomena. Here we report our early results from these experiments on samples of polyether ether ketone thermoplastic polymer material. Irradiating using a range of electron currents provides insight into the effect not just of inherent material properties but also of secondary effects such as radiation-induced conductivity.