Test Particle Energization by Current Sheets and Nonuniform Fields in Magnetohydrodynamic Turbulence

Dmitruk, P.; Matthaeus, W. H.; Seenu, N.

doi:10.1086/425301

Cited by 246 publications

(275 citation statements)

References 44 publications

Supporting

Mentioning

260

Contrasting

Order By: Relevance

“…Overall, this behavior is similar to the "proton" case in Ref. [26], where a ten times stronger mean field resulted in much faster acceleration. Consequently test particles in our simulations stay well below the maximum energy derived in that reference.…”

supporting

confidence: 83%

Acceleration of particles in imbalanced magnetohydrodynamic turbulence

et al. 2014

View full text Add to dashboard Cite

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...

show abstract

supporting

confidence: 83%

Acceleration of particles in imbalanced magnetohydrodynamic turbulence

et al. 2014

View full text Add to dashboard Cite

show abstract

“…In previous papers describing particle acceleration, it has been seen that the particles undergo repeated acceleration and deacceleration as they pass through the turbulent magnetic field domain (Dmitruk et al 2004;Dmitruk & Matthaeus 2006;Turkmani et al 2006). In this experiment we assume that a single coherent current sheet is more likely to only provide one single acceleration of the particles, at least for the ones that very rapidly reach the domain boundaries.…”

Section: Individual Acceleration Patternsmentioning

confidence: 96%

“…Mostly these have consisted of situations representing MHD turbulence (Dmitruk et al 2003(Dmitruk et al , 2004Dmitruk & Matthaeus 2006;Turkmani et al 2006) finding the accelerated particles to reach high velocities, having power law distributions with steep power indexes (Turkmani et al 2006). The typical result is that the fastest particles reach energies much higher than found in solar observations.…”

Section: Particle Setupmentioning

confidence: 99%

Test particle acceleration in a numerical MHD experiment of an anemone jet

Rosdahl

Galsgaard²

2010

A&A

View full text Add to dashboard Cite

Aims. To use a 3D numerical MHD experiment representing magnetic flux emerging into an open field region as a background field for tracing charged particles. The interaction between the two flux systems generates a localised current sheet where MHD reconnection takes place. We investigate how efficiently the reconnection region accelerates charged particles and what kind of energy distribution they acquire. Methods. The particle tracing is done numerically using the Guiding Center Approximation on individual data sets from the numerical MHD experiment. Results. We derive particle and implied photon distribution functions having power law forms, and look at the impact patterns of particles hitting the photosphere. We find that particles reach energies far in excess of those seen in observations of solar flares. However the structure of the impact region in the photosphere gives a good representation of the topological structure of the magnetic field.

show abstract

“…Diffusive acceleration of particles by MHD waves was contrasted and compared to direct E-fields and shocks formed by large scale current sheets in the break-up model. Several recent articles showed that the non linear evolution of the MHD waves form small scale structures, which act also as shocks or UCS [23,22,24].…”

Section: The Loop Modelmentioning

confidence: 99%

Magnetic Complexity, Fragmentation, Particle Acceleration and Radio Emission from the Sun

Vlahos

2007

The High Energy Solar Corona: Waves, Eruptions, Particles

View full text Add to dashboard Cite

Abstract. The most popular flare model used to explain the energy release, particle acceleration and radio emission is based on the following assumptions: (1) The formation of a current sheet above a magnetic loop, (2) The stochastic acceleration of particles in the current sheet at the helmet of the loop, (3) the transport and trapping of particles inside the flaring loop. We review the observational consequences of the above model and try to generalize by putting forward a new suggestion, namely assuming that a complex active region driven by the photospheric motions forms naturally a large number of stochastic current sheets that accelerate particles, which in turn can be trapped or move along complex field line structures. The emphasis will be placed on the efficiency and the observational tests of the different models proposed for a flare

show abstract

Test Particle Energization by Current Sheets and Nonuniform Fields in Magnetohydrodynamic Turbulence

Cited by 246 publications

References 44 publications

Acceleration of particles in imbalanced magnetohydrodynamic turbulence

Acceleration of particles in imbalanced magnetohydrodynamic turbulence

Test particle acceleration in a numerical MHD experiment of an anemone jet

Magnetic Complexity, Fragmentation, Particle Acceleration and Radio Emission from the Sun

Contact Info

Product

Resources

About