Stochastic Electron Acceleration by Temperature Anisotropy Instabilities Under Solar Flare Plasma Conditions

Abstract

Using 2D particle-in-cell (PIC) plasma simulations we study electron acceleration by temperature anisotropy instabilities, assuming conditions typical of above-the-loop-top (ALT) sources in solar flares. We focus on the long-term effect of $T_{e,\perp }>T_{e,\parallel }$ instabilities by driving the anisotropy growth during the entire simulation time, through imposing a shearing or a compressing plasma velocity ($T_{e,\perp }$ and $T_{e,\parallel }$ are the temperatures perpendicular and parallel to the magnetic field). This magnetic growth makes $T_{e,\perp }/T_{e,\parallel }$ grow due to electron magnetic moment conservation, and amplifies the ratio ${\omega }_{ce}/{\omega }_{pe}$ from $\sim 0.53$ to $\sim 2$ (${\omega }_{ce}$ and ${\omega }_{pe}$ are the electron cyclotron and plasma frequencies, respectively). In the regime ${\omega }_{ce}/{\omega }_{pe}\lesssim 1.2-1.7$ the instability is dominated by oblique, quasi-electrostatic (OQES) modes, and the acceleration is inefficient. When ${\omega }_{ce}/{\omega }_{pe}$ has grown to ${\omega }_{ce}/{\omega }_{pe}\gtrsim 1.2-1.7$, electrons are efficiently accelerated by the inelastic scattering provided by unstable parallel, electromagnetic z (PEMZ) modes. After ${\omega }_{ce}/{\omega }_{pe}$ reaches $\sim 2$, the electron energy spectra show nonthermal tails that differ between the shearing and compressing cases. In the shearing case, the tail resembles a power-law of index ${\alpha }_s\sim$ 2.9 plus a high-energy bump reaching $\sim 300$ keV. In the compressing runs, ${\alpha }_s\sim$ 3.7 with a spectral break above $\sim 500$ keV. This difference can be explained by the different temperature evolutions in these two types of simulations, suggesting a critical role played by the type of anisotropy driving, ${\omega }_{ce}/{\omega }_{pe}$ and the electron temperature in the efficiency of the acceleration.

arXiv comment15 pages, 13 figures

References in corpus (38)

• An Observational Overview of Solar Flares
• Imaging coronal magnetic-field reconnection in a solar flare
• Stochastic Acceleration of Electrons and Protons. I. Acceleration by Parallel Propagating Waves
• Electron Heating in Hot Accretion Flows
• Stochastic Acceleration by Turbulence
• The power-law spectra of energetic particles during multi-island magnetic reconnection
• Acceleration and propagation of Solar Energetic Particles
• Particle Acceleration by a Solar Flare Termination Shock
• Measurement of magnetic field and relativistic electrons along a solar flare current sheet
• Double Coronal Hard and Soft X-ray Source Observed by RHESSI: Evidence for Magnetic Reconnection and Particle Acceleration in Solar Flares
• Electron Acceleration during Macroscale Magnetic Reconnection
• PIC Simulations of Continuously Driven Mirror and Ion Cyclotron Instabilities in High Beta Astrophysical and Heliospheric Plasmas
• Formation of Power-law Electron Energy Spectra in Three-dimensional Low-$\beta$ Magnetic Reconnection
• Electron Power-Law Spectra in Solar and Space Plasmas
• Mapping the magnetic field of flare coronal loops
• Electron Heating by the Ion Cyclotron Instability in Collisionless Accretion Flows. I. Compression-Driven Instabilities and the Electron Heating Mechanism
• Local 2D Particle-in-cell simulations of the collisionless MRI
• Magnetohydrodynamic shocks in and above post-flare loops: two-dimensional simulation and a simplified model
• The Mechanisms of Electron Acceleration During Multiple X Line Magnetic Reconnection with a Guide Field
• PIC Simulations of the Effect of Velocity Space Instabilities on Electron Viscosity and Thermal Conduction
• Plasma Energization in Colliding Magnetic Flux Ropes
• NHDS: The New Hampshire Dispersion Relation Solver
• The Dynamical Behavior of Reconnection-driven Termination Shocks in Solar Flares: Magnetohydrodynamic Simulations
• The Acceleration of Charged Particles and Formation of Power-law Energy Spectra in Nonrelativistic Magnetic Reconnection
• Evolution of a Current Sheet in a Solar Flare
• Energetic Electron Distribution of the Coronal Acceleration Region: First results from Joint Microwave and Hard X-ray Imaging Spectroscopy
• Electron Heating by the Ion Cyclotron Instability in Collisionless Accretion Flows. II. Electron Heating Efficiency as a Function of Flow Conditions
• Radio Spectroscopic Imaging of a Solar Flare Termination Shock: Split-Band Feature as Evidence for Shock Compression
• Radio Spectral Imaging of an M8.4 Eruptive Solar Flare: Possible Evidence of a Termination Shock
• Drift-Kinetic Modeling of Particle Acceleration and Transport in Solar Flares
• Dynamical modulation of solar flare electron acceleration due to plasmoid-shock interactions in the looptop region
• PIC Simulations of Velocity-Space Instabilities in a Decreasing Magnetic Field: Viscosity and Thermal Conduction
• Direct Observation of Two-Step Magnetic Reconnection in a Solar Flare
• Coronal Electron Distribution in Solar Flares: Drift-Kinetic Model
• Observations of Reconnection Flows in a Flare on the Solar Disk
• Stochastic Ion Acceleration by the Ion-cyclotron Instability in a Growing Magnetic Field
• Stochastic Electron Acceleration by the Whistler Instability in a Growing Magnetic Field
• Stochastic Acceleration of Electrons by Fast Magnetosonic Waves in Solar Flares: the Effects of Anisotropy in Velocity andWavenumber Space

Cited by in corpus (2)

• A Heating Mechanism via Magnetic Pumping in the Intracluster Medium
• Transport of electrons in tangled magnetic fields