Low‐Resource Technique for Measurement of H ⁺ and O ⁺ in the Terrestrial Magnetosphere

Measurement of O⁺ in the Earth's magnetosphere is important for monitoring and understanding the initiation and evolution of geomagnetic activity. During active times, O⁺ can be the most abundant ion in the magnetosphere. Furthermore, because O⁺ and H⁺ damage exposed spacecraft materials through different processes, measurement and prediction of O⁺ and H⁺ fluxes is critical for understanding cumulative damage effects to these materials resulting from the ambient plasma environment of a spacecraft. We describe a simple technique for quantitative, in situ measurement of O⁺ and H⁺ fluxes using ultrathin foils. This technique is a low–resource addition to a standard electrostatic energy–per–charge analyzer followed by an array of detectors. H⁺ and O⁺ abundances up to a few tens of keV can be determined by comparison of counts in detectors having no ultrathin foil at the detector aperture, in which both H⁺ and O⁺ are detected, and adjacent detectors having a foil over the aperture of the appropriate thickness to stop the transmission of O⁺ but through which H⁺ can transit. We describe three techniques for implementing this method enabling differentiation of O⁺ and H⁺ in an instrument package significantly simpler than traditional mass spectrometers.