Measurement Methods of Electron Emission Over a Full Range of Sample Charging

The electron emission properties of a material subject to incident radiation flux are key parameters in determining to what equilibrium charge a spacecraft will established under given environmental conditions. However, there is a complex relation between these emission properties and the charge built up in spacecraft insulators. Complex modeling codes have been developed to predict the potential a spacecraft will adopt as a consequence of its interaction with the space plasma. These require correct models of the electron yields as a function of charge to accurately predict the both the charge build up and the equilibrium potential of spacecraft components. This paper focuses on different methods appropriate to determine the fundamental electronic material property of total electron yield as the materials accumulates charge. Three methods for determining the uncharged total yield are presented: (i) The DC Continuous Beam Method is a relatively easy and accurate method appropriate for conductors and semi-conductors with maximum total electron yield σmaxρ\u3c106 \u3eΩ-cm. (ii) The Pulse-Yield Method seeks to minimize the effects of charging and is applicable to materials with σmaxρ up to \u3e1024 Ω-cm. (iii) The Yield Decay Method is a very difficult and time consuming that uses a combination of measurement and modeling to measure the most difficult materials with σmax\u3e4 and ρ up to \u3e1024 Ω-cm. Data for high purity polycrystalline Au, Kapton HN, and polycrystalline aluminum oxide ceramic are presented. These data demonstrate the relative strengths and weaknesses of each method, but more importantly show that the methods described herein are capable of reliably measuring the total electron yield of almost any spacecraft material