Dynamics of double layers, ion acceleration and heat flux suppression during solar flares

TL;DR

This study uses large-scale PIC simulations to investigate how multiple double layers in the solar corona influence electron confinement, ion acceleration, and heat flux suppression during solar flares, providing insights into solar wind formation.

Contribution

It reveals the dynamics of multiple double layers in larger systems, showing their role in electron confinement and ion acceleration, which was not previously understood in smaller-scale models.

Findings

Multiple double layers generate high-velocity electron beams.

Double layers trap electrons, suppressing transport.

Ion acceleration occurs over extended regions.

Abstract

Observations of flare-heated electrons in the corona typically suggest confinement of electrons. The confinement mechanism, however, remains unclear. The transport of coronal hot electrons into ambient plasma was recently investigated by particle-in-cell (PIC) simulations. Electron transport was significantly suppressed by the formation of a highly localized, nonlinear electrostatic electric potential in the form of a double layer (DL). In this work large-scale PIC simulations are performed to explore the dynamics of DLs in larger systems where, instead of a single DL, multiple DLs are generated. The primary DL accelerates return current electrons, resulting in high velocity electron beams that interact with ambient ions. This forms a Buneman unstable system that spawns more DLs. Trapping of heated return current electrons between multiple DLs strongly suppresses electron transport. DLs also accelerate ambient ions and produce strong ion flows over an extended region. This clarifies the mechanism by which hot electrons in the corona couple to and accelerate ions to form the solar wind. These new dynamics in larger systems reveal a more likely picture of DL development and their impact on the ambient plasma in the solar corona. They are applicable to the preparation for in-situ coronal space missions like the Solar Probe Plus.