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

Spacecraft charging codes require accurate models of electron yields as a function of accumulated charge to correctly predict the charge buildup on spacecraft. The accumulated charge creates equilibrium surface potentials on spacecraft resulting from interactions with the space plasma environment. There is, however, a complex relation between these emission properties and the charge built up in spacecraft insulators. This paper focuses on different methods appropriate to determine the fundamental electronic material property of the total electron yield as the materials accumulate charge. Three methods for determining the uncharged total yield are presented: 1) The dc continuous beam method is a relatively easy and accurate method appropriate for conductors and semiconductors with maximum total electron yield σ_max <; 2 and resistivity ρ <; 10¹⁷ Ω·cm; 2) the pulsed-yield method seeks to minimize the effects of charging and is applicable to materials with σ_max <; 4 and ρ up to >; 10²⁴ Ω·cm; and 3) the yield decay method is a very difficult and time-consuming technique that uses a combination of measurement and modeling to investigate the most difficult materials with σ_max >; 4 and ρ up to <; 10²⁴ Ω·cm. Data for high-purity polycrystalline Au, Kapton HN and CP1 polyimides, 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.