[IGPP Everyone] NOW: Space Physics Seminar: Transition to fast reconnection in thin current sheets. (A. Tenerani, EPSS)

[Emmanuel V. Masongsong]

SPACE PHYSICS SEMINAR 

DEPARTMENT OF EARTH, PLANETARY, AND SPACE SCIENCES 

DEPARTMENT OF ATMOSPHERIC AND OCEANIC SCIENCES 

UNIVERSITY OF CALIFORNIA, LOS ANGELES 

(EPSS M288A, AOS M275A ) 







Anna Tenerani 


UCLA EPSS & IGPP 





Transition to Fast Reconnection in Thin Current Sheets 








Abstract: 
Magnetic reconnection is a process whereby magnetic energy is converted locally into particle heat and kinetic energy via some mechanism of dissipation allowing a change of the global magnetic topology. Reconnection is thought to be the underlying mechanism of many explosive processes observed in nature, such as solar flares and geomagnetic substorms, and is also invoked as the counterpart to wave-turbulence driven stellar winds. How fast magnetic energy release is triggered and develops in high Lundquist (S) and Reynolds (R) number plasmas, as those found in space, is a fundamental problem for understanding phenomena ranging from coronal heating to flares and CMEs. Many energy release events that are believed to be produced by reconnection show a first build-up stage where energy is stored during a long period, and a subsequent abrupt disruptive stage. On the other hand, how reconnection could explain the explosive phase of such phenomena is still far from being understood: pure diffusion or resistive reconnection driven by macroscopic flows in quasi-steady Sweet-Parker (SP) current sheets are processes far too slow to fit observational data. Spontaneous reconnection as the outcome of the onset of an internal instability inside current sheets, namely, the Tearing instability, provides an alternative paradigm to SP reconnection. Nevertheless, as long as macroscopic current layers are considered, the growth of such instability is also a slow process, with respect to the Alfvén time. Recently, there has been a renewed interest on the resistive tearing instability and SP current sheets, as it has been shown that the latter are rapidly tearing-unstable in high S plasmas (“plasmoid instability”), thus speeding up the reconnection rate, which indeed is diverging in the ideal limit of increasing S. In this seminar I will discuss some recent advances in the understanding of how fast reconnection can be triggered in high Lundquist and Reynolds number plasmas, showing that it is in general possible to find a threshold of the system marking the transition from quasi stable to ideally unstable current sheets. 



Friday, March 6, 2015 

Room 6704 Geology 

3:30 - 5:00 PM 



Refreshments served after the seminar in Room 6850. 



In-Charge 
V. Angelopoulos 


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