Electron Yield Measurements of Highly Insulating Granular Samples Related to Charging of Dusty Plasmas

Lack of reliable electron yield (EY) measurements of highly insulating granular particles due to many experimental complexities have led to a critical knowledge gap for both engineering strategies and basic science issues essential to charging in myriad dusty plasma and space applications. EY measurements are presented, which demonstrate the ability to acquire accurate EY versus incident energy curves with minimal charging effects. Measurements studied different composition non-conductive particulate samples adhered to graphitic carbon conductive substrates, for cubic, spherical, and highly-angular particle shapes with a range particle size from ~1 to ~100 μm. Results for various size particles from 0% to ~100% coverage demonstrated the effectiveness of the dust sample preparation and tests methods. Acquired EY curves showed minimal charging effects, demonstrating our ability to measure EY for very high-yield, highly insulating samples, in contrast to previous results for dust which showed highly suppressed yields due to severe charging effects. The effects of surface roughness porosity, and compactness were investigated through comparison of EY for highly polished single crystal sapphire, rougher microcrystalline Al₂O₃, and very rough and porous layers of granular alumina; maximum yield decreased from >15 to ~2.2 as roughness increased with minimal change in shape of the yield curves and energy at maximum yield. Applications of these results to issues surrounding mitigation of electrostatic charging of lunar dust are discussed.