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Superdiffusive transport in laboratory and astrophysical plasmas

Part of: Complex Plasma Phenomena

Published online by Cambridge University Press:  01 October 2015

G. Zimbardo ,
E. Amato ,
A. Bovet Open the ORCID record for A. Bovet [Opens in a new window] ,
F. Effenberger ,
A. Fasoli ,
H. Fichtner ,
I. Furno ,
K. Gustafson ,
P. Ricci  and
S. Perri
G. Zimbardo*
Affiliation:
Department of Physics, University of Calabria, Ponte P. Bucci, Cubo 31C, I-87036 Rende, Italy
E. Amato
Affiliation:
INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
A. Bovet
Affiliation:
Ecole Polytechnique Federale Lausanne, EPFL, Lausanne, CH-1015, Switzerland
F. Effenberger
Affiliation:
Department of Physics and KIPAC, Stanford University, Stanford, CA 94305, USA Department of Mathematics, University of Waikato, P.B. 3105, Hamilton, New Zealand
A. Fasoli
Affiliation:
Ecole Polytechnique Federale Lausanne, EPFL, Lausanne, CH-1015, Switzerland
H. Fichtner
Affiliation:
Institut für Theoretische Physik IV, Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany
I. Furno
Affiliation:
Ecole Polytechnique Federale Lausanne, EPFL, Lausanne, CH-1015, Switzerland
K. Gustafson
Affiliation:
Ecole Polytechnique Federale Lausanne, EPFL, Lausanne, CH-1015, Switzerland
P. Ricci
Affiliation:
Ecole Polytechnique Federale Lausanne, EPFL, Lausanne, CH-1015, Switzerland
S. Perri
Affiliation:
Department of Physics, University of Calabria, Ponte P. Bucci, Cubo 31C, I-87036 Rende, Italy
*
†Email address for correspondence: gaetano.zimbardo@fis.unical.it
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Abstract

In the last few years it has been demonstrated, both by data analysis and by numerical simulations, that the transport of energetic particles in the presence of magnetic turbulence can be superdiffusive rather than normal diffusive (Gaussian). The term ‘superdiffusive’ refers to the mean square displacement of particle positions growing superlinearly with time, as compared to the normal linear growth. The so-called anomalous transport, which in general comprises both subdiffusion and superdiffusion, has gained growing attention during the last two decades in many fields including laboratory plasma physics, and recently in astrophysics and space physics. Here we show a number of examples, both from laboratory and from astrophysical plasmas, where superdiffusive transport has been identified, with a focus on what could be the main influence of superdiffusion on fundamental processes like diffusive shock acceleration and heliospheric energetic particle propagation. For laboratory plasmas, superdiffusion appears to be due to the presence of electrostatic turbulence which creates long-range correlations and convoluted structures in perpendicular transport: this corresponds to a similar phenomenon in the propagation of solar energetic particles (SEPs) which leads to SEP dropouts. For the propagation of energetic particles accelerated at interplanetary shocks in the solar wind, parallel superdiffusion seems to be prevailing; this is based on a pitch-angle scattering process different from that envisaged by quasi-linear theory, and this emphasizes the importance of nonlinear interactions and trapping effects. In the case of supernova remnant shocks, parallel superdiffusion is possible at quasi-parallel shocks, as occurring in the interplanetary space, and perpendicular superdiffusion is possible at quasi-perpendicular shocks, as corresponding to Richardson diffusion: therefore, cosmic ray acceleration at supernova remnant shocks should be formulated in terms of superdiffusion. The possible relations among anomalous transport in laboratory, heliospheric, and astrophysical plasmas will be indicated.

Type
Research Article
Information
Journal of Plasma Physics , Volume 81 , Issue 6 , December 2015 , 495810601
Copyright
© Cambridge University Press 2015 

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