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Chaotic advection and particle pairs diffusion in a low-dimensional truncation of two-dimensional magnetohydrodynamics
Univ Calabria, Inst Atmospher Pollut Res, CNR, I-87036 Arcavacata Di Rende, Italy..ORCID iD: 0000-0002-3559-5273
Astrophys Observ Torino, Natl Inst Astrophys, Via Osservatorio 20, I-10025 Pino Torinese, Italy..
Univ Alabama, Ctr Space Plasma & Aeron Res CSPAR, Huntsville, AL 35899 USA.;Univ Alabama, Dept Space Sci, Huntsville, AL 35899 USA..
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division. CNR, Ist Sci & Tecnol Plasmi, Via Amendola 122-D, I-70126 Bari, Italy..ORCID iD: 0000-0002-5981-7758
2022 (English)In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 138, no 5, article id 53001Article in journal (Refereed) Published
Abstract [en]

The chaotic advection of fluid particle pairs is investigated though a low-order model of two-dimensional magnetohydrodynamic (MHD), where only five nonlinearly interacting modes are retained. The model is inthrinsically inhomogeneous and anisotropic because of the influence of large-scale fluctuations. Therefore, even though dynamically chaotic, the fields are unable to form the typical scaling laws of fully developed turbulence. Results show that a super-ballistic dynamics, reminiscent of the Richardson law of particle-pairs diffusion in turbulent flows, is robustly obtained using the truncated model. Indeed, even in the strongly reduced truncation presented here, particle diffusion in MHD turbulence has the same laws as the separation of velocity of particle pairs. The inherent anisotropy only affects the scaling of diffusivity, by enhancing the diffusion properties along one direction for small time-scales. Finally, when further anisotropy is introduced in the system through Alfven waves, fluid particles are trapped by these, and super-ballistic diffusion is replaced by Brownian-like diffusion. On the other hand, when the magnetic field is removed, the kinetic counterpart of the model does not show super-ballistic dynamics.

Place, publisher, year, edition, pages
IOP Publishing Institute of Physics (IOP), 2022. Vol. 138, no 5, article id 53001
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-478820DOI: 10.1209/0295-5075/ac7250ISI: 000810183900001OAI: oai:DiVA.org:uu-478820DiVA, id: diva2:1676778
Available from: 2022-06-27 Created: 2022-06-27 Last updated: 2024-12-03Bibliographically approved

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Sorriso-Valvo, Luca

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