Ion Traps at the Sun: Implications for Elemental Fractionation

TL;DR

This paper combines theoretical predictions and observational data to identify regions in the solar corona, called 'ion traps,' where heavy ions accumulate in magnetic flux tubes, impacting elemental fractionation and coronal diagnostics.

Contribution

It introduces the concept of 'ion traps' in the solar corona, linking electric current density with heavy ion concentration, and provides observational evidence for these regions.

Findings

Significant EUV brightness excess in areas with positive current density.

Discovery of heavy ion concentrations in current-carrying magnetic flux tubes.

Ion traps influence elemental fractionation in the solar corona.

Abstract

Why the tenuous solar outer atmosphere, or corona, is much hotter than the underlying layers remains one of the greatest challenge for solar modeling. Detailed diagnostics of the coronal thermal structure come from extreme ultraviolet (EUV) emission. The EUV emission is produced by heavy ions in various ionization states and depends on the amount of these ions and on plasma temperature and density. Any nonuniformity of the elemental distribution in space or variability in time affects thermal diagnostics of the corona. Here we theoretically predict ionized chemical element concentrations in some areas of the solar atmosphere, where the electric current is directed upward. We then detect these areas observationally, by comparing the electric current density with the EUV brightness in an active region. We found a significant excess in EUV brightness in the areas with positive current density rather than negative. Therefore, we report the observational discovery of substantial concentrations of heavy ions in current-carrying magnetic flux tubes, which might have important implications for the elemental fractionation in the solar corona known as the first ionization potential (FIP) effect. We call such areas of heavy ion concentration the "ion traps." These traps hold enhanced ion levels until they are disrupted by a flare whether large or small.