Statistical study of heavy ion energization in the near-Earth magnetotail using an energy channel cross-correlation approach

We present a statistical study of heavy ion acceleration in the near-Earth magnetotail using observations from the Energetic Ion Spectrometer (EIS) onboard Magnetospheric Multiscale (MMS) spacecraft. Although the EIS instrument does not measure ion charge state directly, using a previously developed correlation analysis of the flux response between different energy channels of different ion species, we are able to infer the dominant charge state of the suprathermal heavy ions (50-1000 keV) and distinguish adiabatic (charge-dependent) energization from non-adiabatic (mass-dependent) energization. This work uses observations from the MMS Bursty Bulk Flows (BBF) Campaign in August 2016, when high-energy-resolution burst-mode data are more frequently available, to examine the relative occurrence of adiabatic energization versus preferential energization of heavy ions. The results of this study demonstrate the utility and limitations of the cross-correlation technique and provide further evidence that high-energy total ion measurements in the magnetosphere are dominated by high-charge-state heavy ions.