Particle acceleration by sub-proton cyclotron frequency spectrum of dispersive Alfven waves in inhomogeneous solar coronal plasmas

Abstract

The problem of explaining observed soft X-ray fluxes during solar flares, which invokes acceleration of large fraction of electrons, if the acceleration takes places at the solar coronal loop-top, can potentially be solved by postulating that flare at loop-top creates dispersive Alfven waves (DAWs) which propagate towards the foot-points. As DAWs move in progressively denser parts of the loop (due to gravitational stratification) the large fraction of electrons is no longer needed. Here we extend our previous results by considering $f^{-1}$ frequency spectrum of DAWs and add $\mathrm{H}{\mathrm{e}}^{++}$ ions using fully kinetic particle-in-cell (PIC) simulations. We consider cases when transverse density gradient is in the range $4-40c/{\omega }_{\mathrm{pe}}$ and DAW driving frequency is $0.3-0.6{\omega }_{\mathrm{cp}}$. We find that (i) The frequency spectrum case does not affect electron acceleration fraction in the like-to-like cases, but few times larger percentage of $\mathrm{H}{\mathrm{e}}^{++}$ heating is seen due to ion cyclotron resonance; (ii) In cases when counter propagating DAWs collide multiple-times, much larger electron and ion acceleration fractions are found, but the process is intermittent in time. This is because intensive heating (temperature increase) makes the-above-thermal-fraction smaller; Also more isotropic velocity distributions are seen; (iii) Development of kink oscillations occurs when DAWs collide; (iv) Scaling of the magnetic fluctuations power spectrum steepening in the higher-density regions is seen, due to wave refraction. Our PIC runs produce much steeper slopes than the orginal spectrum, indicating that the electron-scale physics has a notable effect of DAW spectrum evolution.

The final version accepted for publication in Monthly Notices of the Royal Astronomical Society (MNRAS)

References in corpus (17)

• Impulsive phase flare energy transport by large-scale Alfven waves and the electron acceleration problem
• Advances in Observing Various Coronal EUV Waves in the SDO Era and Their Seismological Applications (Invited Review)
• Revisiting a classic: the Parker-Moffatt problem
• Relative drifts and temperature anisotropies of protons and $\alpha$ particles in the expanding solar wind -- 2.5D hybrid simulations
• Transition to kinetic turbulence at proton scales driven by large-amplitude Kinetic Alfvèn fluctuations
• The radial variation of the solar wind turbulence spectra near the kinetic break scale from Parker Solar Probe measurements
• Traveling kink oscillations of coronal loops launched by a solar flare
• Spectrum of kinetic plasma turbulence at 0.3-0.9 astronomical units from the Sun
• Excitation and Damping of Slow Magnetosonic Waves in Flaring Hot Coronal Loops: Effects of Compressive Viscosity
• Excitation of flare-induced waves in coronal loops and the effects of radiative cooling
• Nonlinear Landau resonant interaction between kinetic Alfvén waves and thermal electrons: Excitation of time domain structures
• A minimal model of parallel electric field generation in a transversely inhomogeneous plasma
• The efficiency of electron acceleration during the impulsive phase of a solar flare
• Enhanced Phase Mixing of Torsional Alfvén Waves in Stratified and Divergent Solar Coronal Structures, Paper II: Nonlinear Simulations
• Collisionless, phase-mixed, dispersive, Gaussian Alfven pulse in transversely inhomogeneous plasma
• Electron acceleration from the interaction of three crossed parallel Alfvén waves
• Electron acceleration and small scale coherent structures formation by an Alfvén wave propagating in coronal interplume region

Cited by in corpus (1)

• The effect of external magnetic field on electron scale Kelvin-Helmholtz instability