Coronal Electron Confinement by Double Layers

Abstract

In observations of flare-heated electrons in the solar corona, a longstanding problem is the unexplained prolonged lifetime of the electrons compared to their transit time across the source. This suggests confinement. Recent particle-in-cell (PIC) simulations, which explored the transport of pre-accelerated hot electrons through ambient cold plasma, showed that the formation of a highly localized electrostatic potential drop, in the form of a double layer (DL), significantly inhibited the transport of hot electrons (T.C. Li, J.F. Drake, and M. Swisdak, 2012, ApJ, 757, 20). The effectiveness of confinement by a DL is linked to the strength of the DL as defined by its potential drop. In this work, we investigate the scaling of the DL strength with the hot electron temperature by PIC simulations, and find a linear scaling. We demonstrate that the strength is limited by the formation of parallel shocks. Based on this, we analytically determine the maximum DL strength, and find also a linear scaling with the hot electron temperature. The DL strength obtained from the analytic calculation is comparable to that from the simulations. At the maximum strength, the DL is capable of confining a significant fraction of hot electrons in the source.

References in corpus (3)

• Relations between concurrent hard X-ray sources in solar flares
• Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares
• Footpoint versus loop-top hard X-ray emission sources in solar flares

Cited by in corpus (7)

• Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind \textit{(Invited Review)}
• The Acceleration and Confinement of Energetic Electrons by a Termination Shock in a Magnetic Trap: An Explanation for Nonthermal Loop-top Sources during Solar Flares
• Wave generation and heat flux suppression in astrophysical plasma systems
• Scattering of energetic electrons by heat-flux-driven whistlers in flares
• Dynamics of double layers, ion acceleration and heat flux suppression during solar flares
• Double layer electric fields aiding the production of energetic flat-top distributions and superthermal electrons within the exhausts from magnetic reconnection
• Expansion of Hot Plasma into Cold Plasma