[seminar] [TODAY @ 11:00] Marina Skender (Thu, 31 Mar, 11:00h, auditorium in building I, IRB)

[Vibor Jelic]

Seminar Zavoda za eksperimentalnu fiziku, Institut Ruđer Bošković
četvrtak, 31. ožujka 2016. u 11h, predavaona I krila, IRB

Seminar of Division of Experimental Physics, Ruđer Bošković Institute
Thursday, 31 March 2016, 11am, auditorium in building I, IRB

dr. sc. Marina Skender
Istituto Nazionale di Astrofisica (INAF), Osservatorio Astronomico di Capodimonte, Napoli, Italy

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On the instability of a quasiequilibrium current sheet and the onset of impulsive bursty reconnection
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All plasmas, whether in the laboratory, the solar system, or the most distant reaches of the universe, generate magnetic fields. The existence of these fields in the presence of plasma flows inevitably leads to the process of magnetic reconnection. Reconnection is a topological restructuring of a magnetic field caused by a change in the connectivity of its field lines. Magnetic reconnection is considered to be a major mechanism for energy release in large-scale solar eruptive phenomena, stellar flares, planetary and cometary magnetospheres, as well as in tokamak disruptions.

In the here presented study long two-dimensional reconnecting current sheet with the X-type of null point is numerically set for the first time in the magnetohydrodynamic approach. Different simulation setups are employed in order to follow the evolution of the formed current sheet in diverse configurations: two types of initial equilibria, Harris and force-free, two types of boundary conditions, periodic and open, with uniform and nonuniform grid set, respectively. All the simulated cases are found to exhibit qualitatively the same behavior in which a current sheet evolves slowly through a series of quasiequilibria; eventually it fragments and enters a phase of fast impulsive bursty reconnection. In order to gain more insight on the nature and characteristics of the instability taking place, physical characteristics of the simulated current sheet are related to its geometrical properties. At the adopted Lundquist number of S =10^4 and Reynolds number R =10^4, the ratio of the length to width (aspect ratio) of the formed current sheet is observed to increase slowly in time up to a maximum value at which it fragments. Moreover, additional turbulence applied to the system is shown to exhibit the same qualitative steps, but with the sooner onset of the fragmentation and at smaller aspect ratio.
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