Particle heating and acceleration by reconnecting and nonreconnecting current sheets

Abstract

In this article, we study the physics of charged particle energization inside a strongly turbulent plasma, where current sheets naturally appear in evolving large-scale magnetic topologies, but they are split into two populations of fractally distributed reconnecting and nonreconnecting current sheets (CS). In particular, we implemented a Monte Carlo simulation to analyze the effects of the fractality and we study how the synergy of energization at reconnecting CSs and at nonreconnecting CSs affects the heating, the power-law high energy tail, the escape time, and the acceleration time of electrons and ions. The reconnecting current sheets systematically accelerate particles and play a key role in the formation of the power-law tail in energy distributions. On the other hand, the stochastic energization of particles through their interaction with nonreconnecting CSs can account for the heating of the solar corona and the impulsive heating during solar flares. The combination of the two acceleration mechanisms (stochastic and systematic), commonly present in many explosive events of various sizes, influences the steady-state energy distribution, as well as the transport properties of the particles in position- and energy-space. Our results also suggest that the heating and acceleration characteristics of ions and electrons are similar, the only difference being the time scales required to reach a steady state.

Preferential Heating of Protons over Electrons from Coherent Structures during the First Perihelion of the Parker Solar Probe

“…The PDFs of the electron and proton temperatures p(T e ) and p(T p ), as well as the PDF of the PVI index p(PVI), are shown separately in blue and red on the top and right margins of the plot. In agreement with previous studies (Osman et al 2012;Yordanova et al 2021;Sioulas et al 2022a), a statistically significant positive correlation is observed with a high PVI index and elevated T p . Nevertheless, the limited number of observations for PVI 4 results in the high variability of T p on the right-hand side of the figure.…”

“…Another potential source of nonadiabatic heating is the magnetohydrodynamic turbulence in the solar wind (Coleman 1968). In particular, observational and numerical studies indicate that plasma heating occurs in an intermittent fashion and suggest a statistical link between coherent magnetic field structures (CSs) and elevated temperatures (Osman et al 2012;Chasapis et al 2015;Yordanova et al 2021;Sioulas et al 2022aSioulas et al , 2022b. The intermittent character of turbulence can be attributed to a fractally distributed population of small-scale CSs, superposed on a background of random fluctuations that, despite occupying only a minor fraction of the entire data set (Vlahos et al 2008;Parashar et al 2009;Osman et al 2012;Wan et al 2012;Sioulas et al 2022aSioulas et al , 2022b can account for a disproportionate amount of magnetic energy dissipation and heating of charged particles (Karimabadi et al 2013;Sioulas et al 2020aSioulas et al , 2020bBandyopadhyay et al 2020).…”

Local Proton Heating at Magnetic Discontinuities in Alfvénic and Non-Alfvénic Solar Wind

“…In the turbulence simulation, once the system reaches the fully developed turbulent state, the energy stored in the fields is progressively converted into thermal energy, resulting in an average (over the spatial domain) preferential perpendicular heating with 〈T ⊥ /T ∥ 〉 box = 1.37 at t 120 ci These different heating processes in the two setups are expected, since the turbulence simulation leads to a welldeveloped magnetic energy spectrum perpendicular (in k space) to the guide field, allowing for more channels of particle heating, such as stochastic heating and particle scattering at current sheets (Cerri et al 2021;Sioulas et al 2022a). Those processes are suppressed in the wave-like simulation due to the different geometry adopted.…”

Cold Solar Flares. I. Microwave Domain

“…Recent simulations (Arnold et al 2021;Sioulas et al 2022) show that the key parameter defining the efficiency of electron acceleration is the ratio between the reconnecting and nonreconnecting magnetic fields, or the "guide" fields. With the increase of the reconnecting field over the guide field and, thus, the increase of the free magnetic energy, the acceleration efficiency goes up.…”