Test-Particle Acceleration in a Hierarchical Three-Dimensional Turbulence Model

Dalena, S.; Rappazzo, A. F.; Dmitruk, P.; Greco, A.; Matthaeus, W. H.

doi:10.1088/0004-637x/783/2/143

Cited by 44 publications

(56 citation statements)

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“…The reduced MHD FLRW properties and topology strongly support the results of recent test-particle simulations (Dalena et al 2014) with initial gyroradii smaller than current sheet widths propagated in similar magnetic fields to those discussed here. Particles are at first strongly accelerated along the z-direction in current sheets by the strong electric field associated with the current, until they pitch-angle scatter thus increasing their gyroradii.…”

Section: Conclusion and Discussionsupporting

confidence: 86%

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Coronal Heating Topology: The Interplay of Current Sheets and Magnetic Field Lines

Rappazzo

Matthaeus

Ruffolo

et al. 2017

ApJ

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The magnetic topology and field line random walk properties of a nanoflare-heated and magnetically confined corona are investigated in the reduced magnetohydrodynamic regime. Field lines originating from current sheets form coherent structures, called Current Sheet Connected (CSC) regions, extended around them. CSC field line random walk is strongly anisotropic, with preferential diffusion along the current sheets' in-plane length. CSC field line random walk properties remain similar to those of the entire ensemble but exhibit enhanced mean square displacements and separations due to the stronger magnetic field intensities in CSC regions. The implications for particle acceleration and heat transport in the solar corona and wind, and for solar moss formation are discussed.

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Section: Conclusion and Discussionsupporting

confidence: 86%

“…Additionally the intense electric fields associated to turbulent coherent structures, such as current sheets (and the related in-and out-flows), strongly contribute to particle acceleration (Swann 1933;Drake et al 2005;Dalena et al 2014). …”

Section: Introductionmentioning

confidence: 99%

Coronal Heating Topology: The Interplay of Current Sheets and Magnetic Field Lines

Rappazzo

Matthaeus

Ruffolo

et al. 2017

ApJ

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“…Unlike previous studies of test-particle acceleration in time-frozen MHD turbulence [26,29,30], our simulations implicitly include the effect of resonance between particles and propagating waves, as the MHD fields are evolved in parallel with the particle trajectories. As the MHD fields evolve in time, the effect of the dynamic fields on the trapping and entrainment of particles is modeled more realistically compared to a frozen-field approach, even though the short time acceleration, as seen in Fig.…”

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confidence: 99%

Acceleration of particles in imbalanced magnetohydrodynamic turbulence

et al. 2014

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The present work investigates the acceleration of test particles, relevant to the solar-wind problem, in balanced and imbalanced magnetohydrodynamic turbulence (terms referring here to turbulent states possessing zero and nonzero cross helicity, respectively). These turbulent states, obtained numerically by prescribing the injection rates for the ideal invariants, are evolved dynamically with the particles. While the energy spectrum for balanced and imbalanced states is known, the impact made on particle heating is a matter of debate, with different considerations giving different results. By performing direct numerical simulations, resonant and nonresonant particle accelerations are automatically considered and the correct turbulent phases are taken into account. For imbalanced turbulence, it is found that the acceleration rate of charged particles is reduced and the heating rate diminished. This behavior is independent of the particle gyroradius, although particles that have a stronger adiabatic motion (smaller gyroradius) tend to experience a larger heating. Introduction. The slow and fast streams in the solar wind represent good examples of balanced and imbalanced states (differing by the level of cross helicity; to be defined below) of magnetohydrodynamic (MHD) turbulence, respectively. This formalism captures the large-scale fluctuations, compared to the proton thermal gyroradius. Although a kinetic approach is needed for the treatment of scales smaller than the proton gyroradius [1,2], where the interaction of kinetic Alfvén waves [3] and electron heating of the solar wind [4] become important, the self-organization of turbulent structures remains predominantly a large-scale effect, determined by fluidlike dynamics.In MHD turbulence, the conservation of cross helicity for the ideal systems represents a dynamical constraint of interest, as it is the quantity that leads to a balanced or imbalanced state of MHD turbulence. While the scaling of the energy spectra for these states has received a lot of attention in recent years [5][6][7], less effort was given to understand the impact on particle acceleration and heating due to the different arrangement of structures. Although it is commonly accepted that the energy transfer rate is reduced in imbalanced MHD turbulence (for which the cross helicity is nonzero) compared to balanced turbulence [8][9][10], the issue of whether particle heating is similarly dependent on the degree of imbalance has been answered differently by different authors. Quasilinear theory, in which the diffusion of particle position and momentum in MHD turbulence is quantified via Fokker-Planck coefficients [11,12], predicts a strong dependence [13,14], although it was recently suggested that the perpendicular heating rate of ions in the solar wind may not be significantly affected by imbalance [15].In this context, two general questions arise: How do dynamical constraints on a macroscopic level, responsible for the self-organization process of turbulent structures, affect the acceleration...

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“…Mechanisms that could pre-energize thermal ions prior to their interaction with magnetic islands include acceleration by parallel electric field or the pickup mechanism discussed below. Such multistage particle acceleration scenarios have previously been discussed, e.g., by Dalena et al (2014). (c) Heating of ions picked up by the reconnection outflow.…”

Section: Particle Acceleration In Coronal Magnetic Reconnectionmentioning

confidence: 95%

Plasma Compression in Magnetic Reconnection Regions in the Solar Corona

Provornikova

Laming

Lukin

2016

ApJ

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It has been proposed that particles bouncing between magnetized flows converging in a reconnection region can be accelerated by the first-order Fermi mechanism. Analytical considerations of this mechanism have shown that the spectral index of accelerated particles is related to the total plasma compression within the reconnection region, similarly to the case of the diffusive shock acceleration mechanism. As a first step to investigate the efficiency of Fermi acceleration in reconnection regions in producing hard energy spectra of particles in the solar corona, we explore the degree of plasma compression that can be achieved at reconnection sites. In particular, we aim to determine the conditions for the strong compressions to form. Using a two-dimensional resistive MHD numerical model, we consider a set of magnetic field configurations where magnetic reconnection can occur, including a Harris current sheet, a force-free current sheet, and two merging flux ropes. Plasma parameters are taken to be characteristic of the solar corona. Numerical simulations show that strong plasma compressions (4) in the reconnection regions can form when the plasma heating due to reconnection is efficiently removed by fast thermal conduction or the radiative cooling process. The radiative cooling process that is negligible in the typical 1 MK corona can play an important role in the low corona/transition region. It is found that plasma compression is expected to be strongest in low-beta plasma β ∼ 0.01-0.07 at reconnection magnetic nulls.

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Test-Particle Acceleration in a Hierarchical Three-Dimensional Turbulence Model

Cited by 44 publications

References 50 publications

Coronal Heating Topology: The Interplay of Current Sheets and Magnetic Field Lines

Coronal Heating Topology: The Interplay of Current Sheets and Magnetic Field Lines

Acceleration of particles in imbalanced magnetohydrodynamic turbulence

Plasma Compression in Magnetic Reconnection Regions in the Solar Corona

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