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

Abstract

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 < 10 17 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 > 10 24 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 < 10 24 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.

Interdependencies Between the Actively Controlled Cluster Spacecraft Potential, Ambient Plasma, and Electric Field Measurements

“…It was found in [23] that the first crossover energy above which the yield function is larger than unity is ∼30-∼40 V for various metals. The yields >1 were measured in [7] for various materials between a few 10 V and 800 eV (Kapton) or 3000 eV (polycrystalline Al 2 O 3 ). Taking these energies from the literature for granted, the potential of a spacecraft charged to positive values well above the peak energy of the secondaries would not be affected by the presence of secondary electrons.…”

“…The list of currents contributing to the spacecraft potential is incomplete without mentioning the secondary electrons ejected from the surface by incoming high-energy electrons. For most spacecraft surface materials, the secondary electron yield function becomes greater than one if the energy of the primary electrons falls into some band [5]- [7]. This means that the plasma electron flux becomes less efficient in lowering the spacecraft potential.…”

Cathodoluminescence studies of defects in coated boron nitride

“…The reduced charging could result from increased total electron emission [28], as well as from increased conductivity which increased charge dissipation. Measurements showed the bulk conductivity of an-BN/Al 2 O 3 was 15 times that of BN and 40 times that of unannealed BN/Al 2 O 3 [27].…”

Space Plasma Interactions with Spacecraft Materials

“…Theoretical models developed over the past several decades allow the extraction of many material parameters from a material's charge/discharge curve, including the density of trapped states (region I), trapping and de-trapping rates, and effective electron mobility (region II), and dark resistivity and conductivity of the material (region III) [24][25][26][27][28].…”