Observations of Suprathermal Ions(5-75 keV) in Association with Shocks

The Heavy Ion Instrument (HIS) onboard Solar Orbiter measures mass, charge, and full 3-D velocities of ions in the energy/charge range 0.5-75keV/charge. Using the data from HIS we study how interplanetary events like shocks or CME fronts create suprathermal tails in the velocity distribution and how those tails change with time. HIS observed the passage of three interplanetary shocks during the period October 2021 - May 2022. The three events were characterized by the acceleration of plasma from the solar wind energy regime (~1keV per amu/charge) to higher energies (5-75 keV), commonly referred to as suprathermal ions; later during the events, energetic particles (100keV and above) were measured by the EPD instrument. This energization process was characterized by a clear dependence upon mass/charge, and found consistent with preferential acceleration of ions present in the high energy tails of solar wind distributions, the seed population. Details of the distribution functions during the three events are presented and contrasted to each other.