Electric field dependence on the conductivity of Kapton-HN: Integration into a 1D physical model used for the description of charge transport in dielectric materials under space environment

International audienceIn this paper, the development of a 1D physical conductivity model that describes charge transport in dielectric materials under space radiations with application to Kapton-HN is discussed. This model allows a good description of the charging behavior in dielectric materials. Former experiment run at ONERA on Kapton-HN showed that conductivity is temperature and electric field dependent. These results confirmed the need of implementing these dependences to our 1D model. This paper focuses on the electric field dependence. After a thorough analysis in the literature, several physical theories have been found that can explain this electric field dependence on the conductivity. They are the Onsager theory and the electric field assisted de-trapping mechanisms: direct tunneling, hopping transport, and the Poole-Frenkel theory. This paper is divided as follows: first the experiments that brought into evidence the electric field dependence of the conductivity in Kapton-HN are pointed out. Then the theories that could explain this dependence are described and implemented into the model. Finally, numerical and experimental conductivity results are compared and presented in the last sections

Study of internal charging of four commonly used polymers through experimental and numerical analysis

International audienceThis paper focuses on the study of internal charging of four space used polymers: polyetheretherketone, fluorinated ethylene propylene, polyimide films, and epoxy based material (Epoxy FR4). Experiments were carried out for each material using the GEODUR facility (Toulouse, ONERA) that mimics the geostationary space environment behind shielding. Two different irradiation currents have been applied: 1 pA/cm2 and 10 pA/cm2. 1 pA/cm2 is used to analyze the charging behavior and the intrinsic electrical properties of each polymer. 10 pA/cm2 is used to study the influence of high electric field levels on their charging behavior. In this paper, two different numerical tools used for the study of internal charging are presented: Monte-Carlo Internal Charging Tool (MCICT) and Transport of Holes and Electrons Model under Irradiation in Space (THEMIS). MCICT has been used in the space community for several years. THEMIS has been recently developed at ONERA and is compared to MCICT. Both numerical tools showed consistent results for the 1 pA/cm2 integrated current but with deviations for the 10 pA/cm2 integrated current, supposedly due to nonlinear electric field effects on charge transport. THEMIS has a more refined physical model for the conductivity than MCICT. It studies more accurately the electron-polymer interactions and the charge transport kinetics of polymers under space radiations. Subsequently, the analysis of the underlying physical phenomena responsible for the polymers’ charging behaviors will be carried out with THEMIS. In addition, studying these phenomena will permit to assess the risks of electrical discharges that may occur on a spacecraft in orbit (e.g., Geostationary (GEO) spacecraft) or during an elliptic trajectory (e.g., sub-GEO) in an Electric Orbit Raising case [E. Y. Choueiri, A. J. Kelly, and R. G. Jahn, J. Spacecr. Rockets 30(6), 749–754 (1993)]

Validation of Internal Charging Tools With Experiments in REEF

The objective of the European Space Agency validation of internal charging tools using the realistic electron environmental facility (REEF) project is to assess the performance of internal charging tools against experimental measurements made at the REEF facility at the University of Surrey. REEF uses an intense strontium-90 beta-emitting radioactive source to simulate the space environment. This project is complemented by parallel experiments to derive material parameters, conducted by ONERA. We report results from REEF with four different types of dielectric material and compare these results to predictions from the DICTAT, MCICT, and NUMIT internal charging simulation tools. The materials under investigation are Cirlex, PEEK, FR4, and Neoflon (FEP). We find that in many cases, the computer codes struggle to recreate REEF results, which raises significant questions over the validity of internal charging mitigation analyses. We show the advantages and disadvantages of each model and suggest what features could be added in order to improve the fidelity of their predictions