Abstract
AbstractLow‐energy ions are difficult to measure, mainly due to spacecraft charging. The ions are attracted to or repelled from the charged surface prior to detection, which changes both the energy and travel direction of the ions. This results in distortions of the data, and the changed travel directions distort the effective field of view (FOV) of the instrument performing the measurements. The ion composition analyzer (RPC‐ICA) was measuring positive ions down to an energy of a few eV around comet 67P/Churyumov‐Gerasimenko. Low‐energy ions play important parts in processes in the cometary environment, but the FOV of RPC‐ICA has been shown to get severely distorted at low ion energies. Several factors are believed to affect the distortion level. In this study we use the Spacecraft Plasma Interaction Software (SPIS) to investigate the influence of varying spacecraft potentials and Debye lengths on the FOV distortion of RPC‐ICA. We show that the distortion level is dependent on the Debye length of the surrounding plasma, but the sensitivity varies substantially between different viewing directions of the instrument. We also show that a small nonlinearity exists in the relation between FOV distortion, ion energy, and spacecraft potential, mainly caused by the photoemission and bulk flow of the cometary plasma.
Highlights
Low‐energy ions play important parts in many processes in planetary environments
We show that a small nonlinearity exists in the relation between field of view (FOV) distortion, ion energy, and spacecraft potential, mainly caused by the photoemission and bulk flow of the cometary plasma
Each cell of the grid corresponds to the nominal FOV of one instrument pixel
Summary
Low‐energy ions play important parts in many processes in planetary environments. Parts of the terrestrial magnetosphere are dominated by low‐energy (tens of eV) ions, which tend to dominate ion outflow and escape (André & Cully, 2012). Low‐energy ions have been shown to influence the dynamics of magnetic reconnection (André et al, 2010). At Mars low‐energy ions have been shown to contribute significantly to the outflow (Dong et al, 2017; Fränz et al, 2015), and the situation is probably similar at Venus (Brace et al, 1987). Low‐energy ion fluxes (
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