Charge-State-Dependent Energization of Suprathermal Ions During Substorm Injections Observed by MMS in the...

Area of Science:

• Space Physics
• Plasma Physics
• Magnetospheric Dynamics

Background:

• Understanding plasma and energetic particle injection from the magnetotail is crucial for magnetospheric dynamics.
• High-energy suprathermal ions play a significant role in these processes.

Purpose of the Study:

• To analyze high-energy suprathermal ion populations during energetic particle enhancement events in the magnetotail.
• To infer dominant charge states of heavy ions using flux correlation analysis.
• To investigate the ordering of ion energization and dispersion by energy per charge state (E/q).

Main Methods:

• Utilized data from the Energetic Ion Spectrometer (EIS) on NASA's Magnetospheric Multiscale (MMS) mission.
• Performed correlation analysis of flux response between different energy channels and ion species (hydrogen, helium, oxygen).
• Examined multiple case studies of energetic particle enhancement events.

Main Results:

• Developed a technique to infer dominant ion charge states without direct measurement.
• Found that ion energization and dispersion are ordered by energy per charge state (E/q) in the magnetotail (7-25 Earth radii).
• Identified solar wind-origin helium and oxygen ions as the highest energy components (≳300 keV), owing to their higher charge states.
• Observed that flux ratios during injections are also well-ordered by E/q.

Conclusions:

• The energy per charge state (E/q) is a key ordering parameter for suprathermal ions in the magnetotail during energetic particle injections.
• Heavy ions, particularly helium and oxygen with higher charge states, are crucial components of high-energy particle populations in the magnetosphere.
• This research enhances our understanding of particle energization and composition within Earth's magnetotail.