Non-adiabatic Oxygen Energization in the near-Earth Magnetotail: MMS Observations

We present observations from the Magnetospheric Multiscale (MMS) mission of a series of substorm-related ion injections on 9 Aug 2016 when MMS was located in the magnetotail between ~7.5-8.5 RE. During these injections there is a strongly species (mass and charge) dependent energization in the highly suprathermal ion populations (50-1000 keV) where oxygen reaches significantly higher peak energies than protons. Using a previously-established correlation technique we are able to conclude that the highest energy (> 400 keV) oxygen ions are multiply charged of solar wind origin, which helps them reach such high energies in rough proportion to their charge states. Additionally, we find that oxygen ions between 130-330 keV are most likely singly-charged, which sometimes achieve higher energizations relative to protons, and specifically, higher than expected based on their charge states. Non-adiabatic processes resulting from the larger gyroradii and/or lower gyroperiods likely boost the oxygen ion energies.

This abstract is submitted in honor of the memory of our dear colleague, Dr. Sam Bingham, who passed away this summer shortly after completing this analysis. Dr. Bingham was a bright and capable young researcher and friend who will be dearly missed.