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

[Carolyn Mueller]

Sorry, this is a HAO-GPT Seminar

Carolyn Mueller wrote:
> *Correction in Name:*
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> 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
>>
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