Fast MHD dissipative processes
We study the time evolution of current sheets under the influence of stagnation point flows driven by external forces. It is shown that significant physical processes occur during the formation of the current sheet, which is originated from the advection of a sparse magnetic flux. The advection and...
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todo:paper_01039733_v26_n3_p637_Gratton2023-10-03T14:57:32Z Fast MHD dissipative processes Gratton, F.T. Bender, L. Gnavi, G. We study the time evolution of current sheets under the influence of stagnation point flows driven by external forces. It is shown that significant physical processes occur during the formation of the current sheet, which is originated from the advection of a sparse magnetic flux. The advection and intensification of the magnetic field at a stagnation flow can give rise to large amounts of Joule dissipation over hydrodynamic time scales. Depending on the balance between the incoming magnetic flux and the dissipation rate, these effects may lead to an accelerated extinction of the magnetic field, the formation of steady state dissipative layers, or to solutions that grow without bound linearly with time. The basic elements of the flow enhanced dissipation mechanism are discussed using order of magnitude considerations. Analytic time dependent solutions that describe the evolution of the magnetic field are obtained for planar flows. Starting from generic initial and boundary conditions for the magnetic field component lying on the plane of the flow, it is shown that the sublayer in which a change of sign of the magnetic field occurs tends to vanish in a short time during the formation of the current sheet. On the other hand, the magnetic field component normal to the flow plane is always rapidly extinguished. Thus, configurations commonly considered as models to steady state reconnection or tearing instability studies, are exceptional cases rather than generic magnetic structures. In three dimensional stagnation flows, all magnetic fields not sustained by a continuous injection of magnetic energy are completely annihilated in a few hydrodynamic times. Self similar solutions that describe the amplification and decay of the magnetic field for planar and axial-symmetric flows are also obtained. Several applications, including solar plasma current sheaths, the dayside magnetospheric stagnation point, and the formation of hot spots in the Plasma Focus experiments, are discussed. The theory of the stability of these dissipative structures is commented upon. Thermal effects due to the rise of the temperature in the current sheath and the ensuing conductivity increment, enhance the amplification and extintion processes. These effects are illustrated with numerical solution examples. Finally, compressibility effects that set a limit to the validity of the solutions are briefly outlined. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_01039733_v26_n3_p637_Gratton |
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Universidad de Buenos Aires |
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I-28 |
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R-134 |
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| description |
We study the time evolution of current sheets under the influence of stagnation point flows driven by external forces. It is shown that significant physical processes occur during the formation of the current sheet, which is originated from the advection of a sparse magnetic flux. The advection and intensification of the magnetic field at a stagnation flow can give rise to large amounts of Joule dissipation over hydrodynamic time scales. Depending on the balance between the incoming magnetic flux and the dissipation rate, these effects may lead to an accelerated extinction of the magnetic field, the formation of steady state dissipative layers, or to solutions that grow without bound linearly with time. The basic elements of the flow enhanced dissipation mechanism are discussed using order of magnitude considerations. Analytic time dependent solutions that describe the evolution of the magnetic field are obtained for planar flows. Starting from generic initial and boundary conditions for the magnetic field component lying on the plane of the flow, it is shown that the sublayer in which a change of sign of the magnetic field occurs tends to vanish in a short time during the formation of the current sheet. On the other hand, the magnetic field component normal to the flow plane is always rapidly extinguished. Thus, configurations commonly considered as models to steady state reconnection or tearing instability studies, are exceptional cases rather than generic magnetic structures. In three dimensional stagnation flows, all magnetic fields not sustained by a continuous injection of magnetic energy are completely annihilated in a few hydrodynamic times. Self similar solutions that describe the amplification and decay of the magnetic field for planar and axial-symmetric flows are also obtained. Several applications, including solar plasma current sheaths, the dayside magnetospheric stagnation point, and the formation of hot spots in the Plasma Focus experiments, are discussed. The theory of the stability of these dissipative structures is commented upon. Thermal effects due to the rise of the temperature in the current sheath and the ensuing conductivity increment, enhance the amplification and extintion processes. These effects are illustrated with numerical solution examples. Finally, compressibility effects that set a limit to the validity of the solutions are briefly outlined. |
| format |
JOUR |
| author |
Gratton, F.T. Bender, L. Gnavi, G. |
| spellingShingle |
Gratton, F.T. Bender, L. Gnavi, G. Fast MHD dissipative processes |
| author_facet |
Gratton, F.T. Bender, L. Gnavi, G. |
| author_sort |
Gratton, F.T. |
| title |
Fast MHD dissipative processes |
| title_short |
Fast MHD dissipative processes |
| title_full |
Fast MHD dissipative processes |
| title_fullStr |
Fast MHD dissipative processes |
| title_full_unstemmed |
Fast MHD dissipative processes |
| title_sort |
fast mhd dissipative processes |
| url |
http://hdl.handle.net/20.500.12110/paper_01039733_v26_n3_p637_Gratton |
| work_keys_str_mv |
AT grattonft fastmhddissipativeprocesses AT benderl fastmhddissipativeprocesses AT gnavig fastmhddissipativeprocesses |
| _version_ |
1807315132400795648 |