Three Solar Irradiance Proxies for Aperture Photoelectron Detections in Top-Hat ESAs Coated With Ebonol-C

Decades after the introduction of top-hat electrostatic analyzers (ESAs) to experimental space plasma physics, photoelectron noise in apertures of low-energy electron instruments continues to be an issue in instrument performance. The photoelectrons at each portion of measured phase space distribution can be mapped through laboratory and in-flight testing, and have been for many missions. In flight, the photoelectrons are a response to dynamic solar EUV spectral intensities which vary over the course of a solar cycle and even within a solar rotation. This paper outlines three solar irradiance proxies that can be used to scale a map of photo-electron locations in phase space in order to account for dynamic solar activity. These proxies apply to top-hat ESAs coated with Ebonol-C (the most common coating) used by missions such as MMS, Solar Orbiter, the Van Allen Probes, and Juno. These proxies are discovered by searching possible wavelengths for correlation with an independent algorithm for MMS/FPI (Magnetospheric Multiscale Mission/Fast Plasma Instrument) which automatically determines the scaling factor. The three wavelengths that serve as viable proxies are found to be: 17.5, 30.5, and 37.5 nm.