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Fast Reconnection in High-Lundquist-Number Plasmas Due to Secondary Tearing Instabilities

Explore onset of fast reconnection in large, high-Lundquist-number systems through thin current sheets dynamics. Mechanisms, instabilities, and implications in resistive MHD investigated.<br>

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Fast Reconnection in High-Lundquist-Number Plasmas Due to Secondary Tearing Instabilities

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  1. Fast Reconnection in High-Lundquist-Number Plasmas Due to Secondary Tearing Instabilities • Bhattacharjee, Y.-M. Huang, H. Yang, and B. Rogers Center for Integrated Computation and Analysis of Reconnection and Turbulence, University of New Hampshire and Dartmouth College

  2. Onset of fast reconnection in large, high-Lundquist-number systems • The scaling of reconnection in large systems is a problem of great interest where the dimensionless ratio of characteristic dissipation scale to system size is a very small number. What are the mechanisms for the onset of fast reconnection in such systems? Does the answer depend on the mechanism that breaks field lines? • One criterion has emerged from Hall MHD (or two-fluid) models, and has been tested carefully in laboratory experiments (MRX at PPPL, VTF at MIT). The criterion is: (Ma and Bhattacharjee 1996, Cassak et al. 2005) or in the presence of a guide field (Aydemir 1992)

  3. Onset of fast reconnection in large, high-Lundquist-number systems (continued) • Here we demonstrate here that within the framework of resistive MHD, extended current sheets form in large systems that become spontaneously unstable to fast, super-Alfvenic tearing instabilities, and produce a time-dependent, nonlinear, impulsive reconnection regime in which the reconnection rate exceeds Sweet-Parker by an order of magnitude (without the intervention of Hall MHD effects).

  4. Super-Alfvenic Tearing Instability of Extended Thin Current Sheets Harris sheet Dispersion relation (Coppi, et al. 1976) Thin current sheets of aspect ratio Fastest growing instability , For Sweet-Parker sheets (Louriero et al., 2007) ,

  5. Summary Onset of fast reconnection, mediated by the dynamics of thin current sheets, in high-Lundquist-number laboratory and space plasmas. Two mechanisms: • Hall MHD, seen in theory and laboratory experiments of moderate size, when the Sweet-Parker width falls below the ion skin depth. This onset can be nonlinearly stabilized due to diamagnetic effects. • Fast, secondary tearing instabilities of thin current sheets in large systems, substantially exceeding Sweet-Parker rates within the realm of resistive MHD (without invoking Hall current and/or electron pressure tensor effects). • Which is the dominant effect?

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