Scattering of Energetic Electrons by Heat-flux-driven Whistlers in Flares

Abstract

The scattering of electrons by heat-flux-driven whistler waves is explored with a particle-in-cell (PIC) simulation relevant to the transport of energetic electrons in flares. The simulation is initiated with a large heat flux that is produced using a kappa distribution of electrons with positive velocity and a cold return current beam. This system represents energetic electrons escaping from a reconnection-driven energy release site. This heat flux system drives large amplitude oblique whistler waves propagating both along and against the heat flux, as well as electron acoustic waves. While the waves are dominantly driven by the low energy electrons, including the cold return current beam, the energetic electrons resonate with and are scattered by the whistlers on time scales of the order of a hundred electron cyclotron times. Peak whistler amplitudes of B/B 0 ∼ 0.125 and angles of ∼ 60 • with respect to the background magnetic field are observed. Electron perpendicular energy is increased while the field-aligned electron heat flux is suppressed. The resulting scattering mean-free-paths of energetic electrons are small compared with the typical scale size of energy release sites in flares, which might lead to the effective confinement of energetic electrons that is required for the production of very energetic particles.

Sunward-propagating Whistler Waves Collocated with Localized Magnetic Field Holes in the Solar Wind: Parker Solar Probe Observations at 35.7 R⊙ Radii

“…(Lacombe et al 2014;Stansby et al 2016;Tong et al 2019a,b;Vasko et al 2019). Such waves are very effective in scattering the Strahl population of solar wind electrons as shown recently in numerical simulations by Roberg-Clark et al (2019). We conjecture that these whistler waves play a significant role in scattering the Strahl population and breaking the heat flux in the inner heliospheric solar wind.…”

“…) on higherorder resonances. Such a scattering by high-amplitude whistler waves (whose amplitude reaches up to 10% of the background magnetic field magnitude) can regulate the heat flux as shown by(Roberg-Clark et al 2019). For that reason the observed high-amplitude waves are likely to be an important factor in the dynamics of the solar wind distribution(Roberg-Clark et al 2018a;Roberg-Clark et al 2018b).…”

Electron temperature of the solar wind

“…Several mechanisms may contribute to the nonadiabatic temperature profile of the solar wind. For instance, the plasma may be heated as a result of instabilities and turbulent fluctuations that extract energy from the streaming motion and convert it into kinetic energy of particles (e.g., Richardson & Smith 2003;Cranmer et al 2007Cranmer et al , 2009Chen 2016;Vech et al 2017;Tang et al 2018;Berčič et al 2019;Verscharen et al 2019a,b;López et al 2019;Shaaban et al 2019;Vasko et al 2019;Roberg-Clark et al 2019). The analysis of such local instabilities, however, does not allow for a definitive prediction of the global radial temperature profile.…”

Long-term dynamics driven by resonant wave–particle interactions: from Hamiltonian resonance theory to phase space mapping

“…2007, 2013; Krafft, Volokitin & Krasnoselskikh 2013; Krafft & Volokitin 2016; Roberg-Clark et al. 2019; Tong et al. 2019).…”