Reconstruction of the ⁴He spectra observed at ACE in the upstream ESP time interval divided into three portions: the pickup ion (He⁺, magenta); the alpha particle (He²⁺, black) spectra, made by shifting the rigidity-scaled Fe spectra into energy space using Equation (2), albeit with the appropriate charge and mass values; and the combination of the two, denoted by the olive line the area where the individual spectra overlap. Panels (a)–(c) show the reconstruction using different values of ϵ from Equation (4). The constants a and b are used to alter the relative concentrations of the two particle populations.