[GTP] Correction- HOA-GTP Seminar January 18, 2012 Amitava Bhattacharjee

[Carolyn Mueller]

*Correction in Name:*



Carolyn Mueller wrote:
> Joint HOA GTP Seminar
> Onset of Fast Reconnection in High-Lundquist-Number Plasmas Mediated 
> by the Plasmoid Instability
>  Amitava Bhattacharjee
> Center for Integrated Computation and Analysis of Reconnection and
> Turbulence, University of New Hampshire, Durham, NH
>
> The problem of fast magnetic reconnection in high-Lundquist-number (S) 
> plasmas has been an active area of research for several decades. The 
> main challenge is to explain why reconnection in nature or laboratory 
> devices (including fusion devices) can proceed rapidly from a 
> relatively quiescent state in a weakly collisional plasma 
> characterized by high values of the Lundquist number (S). The 
> classical Sweet-Parker theory, based on resistive MHD, predicts a 
> reconnection rate that scales as . For many systems of
> interest, the Sweet-Parker reconnection rates are much slower than 
> those observed. Recent work has demonstrated that there is a 
> fundamental flaw in the Sweet-Parker argument, even within the 
> framework of resistive MHD. When the Lundquist number exceeds a 
> critical value, the Sweet-Parker layer is unstable to a super-Alfvenic 
> tearing instability, hereafter referred to as the plasmoid 
> instability, with a growth rate that increases with increasing S. 
> Thus, the original Sweet-Parker current sheet breaks down into a chain 
> of plasmoids and progressively thinner current sheets. Numerical 
> simulations, supported by heuristic scaling arguments, strongly 
> suggest that within the framework of resistive MHD, the nonlinear 
> reconnection rate mediated by the plasmoid instability becomes 
> insensitive to the value of S. Because the plasmoid instability can 
> initiate a cascade to current sheets that are much thinner than the 
> original Sweet-Parker sheet, the so-called Hall terms in the 
> generalized Ohm’s law become important, triggering the onset of Hall 
> reconnection, which lead to higher reconnection rates. We will present 
> recent results from the largest 2D Hall MHD simulations to date that 
> demonstrate the rich dynamics enabled by the interplay between the 
> plasmoid instability and the Hall current. It is shown that the 
> topology of Hall reconnection is not inevitably a single stable 
> X-point. There exists an intermediate regime where the single X-point 
> topology itself exhibits instability, causing the system to alternate 
> between a single X-point and an extended current sheet with multiple 
> X-points produced by the plasmoid instability. Examples of 
> applications will be drawn from laboratory, magnetospheric, and solar 
> coronal plasmas.
>
> Wednesday, January 18, 2012
> Center Green 1, South Auditorium
> Lecture at 1:30pm
>