Publication: Separation of magnetic field lines in two-component turbulence
Issued Date
2004-10-10
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ISSN
15384357
0004637X
0004637X
DOI
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2-s2.0-10844292552
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Mahidol University
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SCOPUS
Bibliographic Citation
Astrophysical Journal. Vol.614, No.1 I (2004), 420-434
Suggested Citation
D. Ruffolo, W. H. Matthaeus, P. Chuychai Separation of magnetic field lines in two-component turbulence. Astrophysical Journal. Vol.614, No.1 I (2004), 420-434. doi:10.1086/423412 Retrieved from: https://repository.li.mahidol.ac.th/handle/20.500.14594/21305
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Title
Separation of magnetic field lines in two-component turbulence
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Abstract
The problem of the separation of random magnetic field lines in collisionless astrophysical plasmas is closely related to the problem of the magnetic field line random walk and is highly relevant to the transport of charged particles in turbulent plasmas. In order to generalize treatments based on quasi-linear theory, here we examine the separation of nearby magnetic field lines by employing a nonperturbative technique based on the Corrsin independence hypothesis. Specifically, we consider the case of two-component turbulence in which the magnetic field fluctuations are a mixture of one-dimensional (slab) and two-dimensional ingredients, as a concrete example of anisotropic turbulence that provides a useful description of turbulence in the solar wind. We find that random field trajectories can separate in general through three regimes of the behavior of the running diffusion coefficient: slow diffusive separation, an intermediate regime of superdiffusion, and fast diffusive separation at large distances. These features are associated with the gradual, exponential divergence of field lines within islands of two-dimensional turbulence, followed by diffusive separation at long distances. The types of behavior are determined not by the Kubo number but rather a related ratio that takes the turbulence anisotropy into account. These results are confirmed by computer simulations. We discuss implications for space observations of energetic charged particles, including "dropouts" of solar energetic particles.