Fe Ion Heating Across a Shock Observed by Solar Orbiter's Heavy Ion Sensor

The ion mass-per-charge (M/Q) and shock geometry determine the number of times a charged particle is reflected across a shock. As such, they govern charged particle acceleration at shocks. This makes high time resolution and charge state separation essential for properly characterizing how shocks energize charged particles.

Solar Orbiter observed a CME on March 11, 2022. During this CME, the Heavy Ion Sensor (HIS) observed heavy ions at its native 30 second cadence. To ensure high quality statistics, we have aggregated our observations to better than 10-minute resolution, an order of magnitude faster than ACE/SWICS' nominal 2-hour resolution. With these observations, we resolve the velocity distribution functions (VDFs) of iron 8+ to 12+ ions. These observations show that solar wind Fe ions are heated in a M/Q-dependent fashion by the shock. This heating is strongest directly at the shock and decreases in strength farther down stream.