MMS Observations of the Charge State and Mass Dependent Energization of Heavy Ions During Injections in the Earth’s Magnetotail

Particle injections transport particles from the Earth’s magnetotail to the inner magnetosphere. During this process, ions in the injections are substantially energized. The physical processes behind this energization are still under debate. Recent results from the Van Allen Probes mission at radial distances < 6 R_E have shown that higher mass ions (helium and oxygen) with high charge states are often found at substantially higher energies than protons (up to MeV energies compared to a couple hundred keV) in the inner magnetosphere. Here we present results from the Magnetospheric Multiscale (MMS) mission over a broad range of radial distances (between 7-25 R_E) where the energization of injected ions is charge state dependent. We demonstrate with these observations that injected ions exhibit behavior which is well ordered by energy per charge due to the gradient/curvature drift’s impact on particle trajectories as they drift in the direction of transient electric fields. The charge state dependent energization leads to the dominance of multiple charge state heavy ions, as opposed to H⁺, above ~250 keV throughout the Earth’s inner and middle magnetosphere. Additionally, there are also cases with hints of non-adiabatic energization observed in O⁺ between ~100-250 keV, where O⁺ potentially gets some extra-energization compared to H⁺ due differences in their respective gyroradii. However, the highest energy ions (> 300 keV oxygen and helium) are still likely of solar wind origin and primarily accelerated due to their higher charge-state. In the process of these results we demonstrate the utility of a technique for deducing ion charge-states using instrumentation that does not directly discriminate by charge state.