Coherent Structures and Spectral Energy Transfer in Turbulent Plasma: A Space-Filter Approach. Camporeale, E., Sorriso-Valvo, L., Califano, F., & Retino, A. PHYSICAL REVIEW LETTERS, MAR 19, 2018.
doi  abstract   bibtex   
Plasma turbulence at scales of the order of the ion inertial length is mediated by several mechanisms, including linear wave damping, magnetic reconnection, the formation and dissipation of thin current sheets, and stochastic heating. It is now understood that the presence of localized coherent structures enhances the dissipation channels and the kinetic features of the plasma. However, no formal way of quantifying the relationship between scale-to-scale energy transfer and the presence of spatial structures has been presented so far. In the Letter we quantify such a relationship analyzing the results of a two-dimensional high-resolution Hall magnetohydrodynamic simulation. In particular, we employ the technique of space filtering to derive a spectral energy flux term which defines, in any point of the computational domain, the signed flux of spectral energy across a given wave number. The characterization of coherent structures is performed by means of a traditional two-dimensional wavelet transformation. By studying the correlation between the spectral energy flux and the wavelet amplitude, we demonstrate the strong relationship between scale-to-scale transfer and coherent structures. Furthermore, by conditioning one quantity with respect to the other, we are able for the first time to quantify the inhomogeneity of the turbulence cascade induced by topological structures in the magnetic field. Taking into account the low space-filling factor of coherent structures (i.e., they cover a small portion of space), it emerges that 80% of the spectral energy transfer (both in the direct and inverse cascade directions) is localized in about 50% of space, and 50% of the energy transfer is localized in only 25% of space.
@article{ ISI:000427804000007,
Author = {Camporeale, E. and Sorriso-Valvo, L. and Califano, F. and Retino, A.},
Title = {{Coherent Structures and Spectral Energy Transfer in Turbulent Plasma: A
   Space-Filter Approach}},
Journal = {{PHYSICAL REVIEW LETTERS}},
Year = {{2018}},
Volume = {{120}},
Number = {{12}},
Month = {{MAR 19}},
Abstract = {{Plasma turbulence at scales of the order of the ion inertial length is
   mediated by several mechanisms, including linear wave damping, magnetic
   reconnection, the formation and dissipation of thin current sheets, and
   stochastic heating. It is now understood that the presence of localized
   coherent structures enhances the dissipation channels and the kinetic
   features of the plasma. However, no formal way of quantifying the
   relationship between scale-to-scale energy transfer and the presence of
   spatial structures has been presented so far. In the Letter we quantify
   such a relationship analyzing the results of a two-dimensional
   high-resolution Hall magnetohydrodynamic simulation. In particular, we
   employ the technique of space filtering to derive a spectral energy flux
   term which defines, in any point of the computational domain, the signed
   flux of spectral energy across a given wave number. The characterization
   of coherent structures is performed by means of a traditional
   two-dimensional wavelet transformation. By studying the correlation
   between the spectral energy flux and the wavelet amplitude, we
   demonstrate the strong relationship between scale-to-scale transfer and
   coherent structures. Furthermore, by conditioning one quantity with
   respect to the other, we are able for the first time to quantify the
   inhomogeneity of the turbulence cascade induced by topological
   structures in the magnetic field. Taking into account the low
   space-filling factor of coherent structures (i.e., they cover a small
   portion of space), it emerges that 80\% of the spectral energy transfer
   (both in the direct and inverse cascade directions) is localized in
   about 50\% of space, and 50\% of the energy transfer is localized in
   only 25\% of space.}},
DOI = {{10.1103/PhysRevLett.120.125101}},
Article-Number = {{125101}},
ISSN = {{0031-9007}},
EISSN = {{1079-7114}},
ResearcherID-Numbers = {{Sorriso-Valvo, Luca/A-9355-2008
   Pegoraro, Francesco/AAF-1392-2020}},
ORCID-Numbers = {{Sorriso-Valvo, Luca/0000-0002-5981-7758
   Pegoraro, Francesco/0000-0002-7216-5491}},
Unique-ID = {{ISI:000427804000007}},
}

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