When do particles follow field lines?

Minnie, J.; Matthaeus, W. H.; Bieber, J. W.; Ruffolo, D.; Burger, R. A.

doi:10.1029/2008ja013349

Cited by 41 publications

(35 citation statements)

References 28 publications

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“…The particle decoupling from field lines has been discussed previously in attempts to understand and develop a theory for the time-asymptotic cross-field diffusion of particles in turbulent magnetic fields (e.g., Qin et al 2002;Matthaeus et al 2009;Ruffolo et al 2012). However, quantifying the process of the particles leaving their field lines presents several challenges.…”

Section: Introductionmentioning

confidence: 99%

Energetic Particle Transport Across the Mean Magnetic Field: Before Diffusion

Laitinen¹,

Dalla

2017

ApJ

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Current particle transport models describe the propagation of charged particles across the mean field direction in turbulent plasmas as diffusion. However, recent studies suggest that at short timescales, such as soon after solar energetic particle (SEP) injection, particles remain on turbulently meandering field lines, which results in nondiffusive initial propagation across the mean magnetic field. In this work, we use a new technique to investigate how the particles are displaced from their original field lines, and we quantify the parameters of the transition from field-aligned particle propagation along meandering field lines to particle diffusion across the mean magnetic field. We show that the initial decoupling of the particles from the field lines is slow, and particles remain within a Larmor radius from their initial meandering field lines for tens to hundreds of Larmor periods, for 0.1-10 MeV protons in turbulence conditions typical of the solar wind at 1 au. Subsequently, particles decouple from their initial field lines and after hundreds to thousands of Larmor periods reach time-asymptotic diffusive behavior consistent with particle diffusion across the mean field caused by the meandering of the field lines. We show that the typical duration of the prediffusive phase, hours to tens of hours for 10 MeV protons in 1 au solar wind turbulence conditions, is significant for SEP propagation to 1 au and must be taken into account when modeling SEP propagation in the interplanetary space.

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Section: Introductionmentioning

confidence: 99%

Energetic Particle Transport Across the Mean Magnetic Field: Before Diffusion

Laitinen¹,

Dalla

2017

ApJ

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“…If particles are tied to magnetic field lines, the maximum perpendicular diffusion rate is set by the rate of perpendicular field line wandering, scaled by particle velocity (field line random walk). This has been extensively discussed by, e.g., Jokipii (1966), Jokipii & Parker (1969), Rechester & Rosenbluth (1978), Giacalone & Jokipii (1999), Yan & Lazarian (2008), Minnie et al (2009), in the context of diffusion at distance scales larger than the turbulence injection scale. On scales smaller than the injection scale, particles are characterized by super-diffusion in the perpendicular direction of the mean magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Cosmic-Ray Small-Scale Anisotropies and Local Turbulent Magnetic Fields

López-Barquero

Farber

Desiati

et al. 2016

ApJ

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Cosmic-ray anisotropy has been observed in a wide energy range and at different angular scales by a variety of experiments over the past decade. However, no comprehensive or satisfactory explanation has been put forth to date. The arrival distribution of cosmicrays at Earth is the convolution of the distribution of their sources and of the effects of geometry and properties of the magnetic field through which particles propagate. It is generally believed that the anisotropy topology at the largest angular scale is adiabatically shaped by diffusion in the structured interstellar magnetic field. On the contrary, the medium-and small-scale angular structure could be an effect of nondiffusive propagation of cosmicrays in perturbed magnetic fields. In particular, a possible explanation forthe observed small-scale anisotropy observed at theTeV energy scalemay be the effect of particle propagation in turbulent magnetized plasmas. We perform numerical integration of test particle trajectories in low-β compressible magnetohydrodynamic turbulence to study how the cosmicrays' arrival direction distribution is perturbed when they stream along the local turbulent magnetic field. We utilize Liouville's theorem for obtaining the anisotropy at Earth and provide the theoretical framework for the application of the theorem in the specific case of cosmic-ray arrival distribution. In this work, we discuss the effects on the anisotropy arising from propagation in this inhomogeneous and turbulent interstellar magnetic field.

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“…It has to be noted that the shape factor is not involved in Eqs. (1) and (2). The dynamic of macro-particles is strictly identical to the one of particles in the present case of a strictly collisionless plasma.…”

Section: Numerical Approachmentioning

confidence: 57%

“…1 This will not be discussed in this paper, even if one has to keep in mind that there is a relation between diffusion and scattering. 2 Particle diffusion in collisionless plasmas is important for instance for cosmic ray modulation in interstellar media, 3 particle confinement in tokamaks, 4 or filling up the magnetosphere with solar wind's particles. 5 In the two first cases, the b value (ratio between kinetic and magnetic pressure) is very low, meaning that the self-consistency is not supposed to be important.…”

Section: Introductionmentioning

confidence: 99%