Scaling Theory for Cross-Field Transport of Cosmic Rays in Turbulent Fields

Hauff, T.; Jenko, F.; Shalchi, A.; Schlickeiser, R.

doi:10.1088/0004-637x/711/2/997

Cited by 46 publications

(54 citation statements)

References 45 publications

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“…Despite important achievements, there are many aspects that are not understood. The field is very active, with many recent papers (see, for instance, Ghilea et al 2011;Hauff et al 2010;Shalchi & Tautz 2011;Snodin et al 2013a that have aims close to that of the present paper, or to the related problem of cosmic ray acceleration Lazarian & Yan 2014).…”

Section: Introductionsupporting

confidence: 53%

“…Other processes, such as small collisional cross field diffusion (Rechester & Rosenbluth 1978, Neur & Spatschek 2008, the intrinsic drift determined by curvature or gradient of B (Vlad et al 1996a), plasma flows (Vlad et al 1996b), or finite Larmor radius effects (Otsuka & Hada 2009), Hauff et al (2010) determine particle departure from the field lines and lead to diffusive transport (see Shalchi 2009 for a review). Besides this strong influence of the characteristics of particle motion, the FLRW remains the fundamental process for understanding particle transport.…”

Section: Introductionmentioning

confidence: 99%

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Diffusion and Stochastic Island Generation in the Magnetic Field Line Random Walk

Vlad

Spineanu

2014

ApJ

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The cross-field diffusion of field lines in stochastic magnetic fields described by the 2D+slab model is studied using a semi-analytic statistical approach, the decorrelation trajectory method. We show that field line trapping and the associated stochastic magnetic islands strongly influence the diffusion coefficients, leading to dependences on the parameters that are different from the quasilinear and Bohm regimes. A strong amplification of the diffusion is produced by a small slab field in the presence of trapping. The diffusion regimes are determined and the corresponding physical processes are identified.

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Section: Introductionsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

Diffusion and Stochastic Island Generation in the Magnetic Field Line Random Walk

Vlad

Spineanu

2014

ApJ

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“…This qualitative connection could be pursued in future work. The relevance of suprathermal ions in astrophysics and space physics phenomena such as cosmic rays and solar flares [11][12][13]43 is also well-known. The general rules found here are relevant in those contexts as well.…”

Section: Discussionmentioning

confidence: 99%

“…Due to its relative simplicity, the SMT successfully disentangles factors that determine suprathermal ion dispersion. Beyond interpretation of TORPEX measurements, this new framework in the generality of the SMT configuration is therefore useful to analyses of more complicated configurations, ranging from fusion devices 9,10 to astrophysics 11,12 and space plasma physics. 13 Our study is based on numerical integration of the charged-particle equation of motion in the SMT environment for a range of injection energies and turbulence fluctuation amplitudes.…”

Section: Introductionmentioning

confidence: 99%

Suprathermal ion transport in simple magnetized torus configurations

et al. 2012

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Inspired by suprathermal ion experiments in the basic plasma experiment TORPEX, the transport of suprathermal ions in ideal interchange mode turbulence is theoretically examined in the simple magnetized torus configuration. We follow ion tracer trajectories as specified by ideal interchange mode turbulence imported from a numerical simulation of drift-reduced Braginskii equations. Using the variance of displacements, σ2(t)∼tγ, we find that γ depends strongly on suprathermal ion injection energy and the relative magnitude of turbulent fluctuations. The value of γ also changes significantly as a function of time after injection, through three distinguishable phases: ballistic, interaction, and asymmetric. During the interaction phase, we find the remarkable presence of three regimes of dispersion: superdiffusive, diffusive, and subdiffusive, depending on the energy of the suprathermal ions and the amplitude of the turbulent fluctuations. We contrast these results with those from a “slab” magnetic geometry in which subdiffusion does not occur during the interaction phase. Initial results from TORPEX are consistent with data from a new synthetic diagnostic used to interpret our simulation results. The simplicity of the simple magnetized torus makes the present work of interest to analyses of more complicated contexts ranging from fusion devices to astrophysics and space plasma physics.

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“…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 of charged particles, and how does this …”

mentioning

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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Scaling Theory for Cross-Field Transport of Cosmic Rays in Turbulent Fields

Cited by 46 publications

References 45 publications

Diffusion and Stochastic Island Generation in the Magnetic Field Line Random Walk

Diffusion and Stochastic Island Generation in the Magnetic Field Line Random Walk

Suprathermal ion transport in simple magnetized torus configurations

Acceleration of particles in imbalanced magnetohydrodynamic turbulence

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