The ideal tearing mode: theory and resistive MHD simulations
Abstract
Classical MHD reconnection theories, both the stationary Sweet-Parker model and the tearing instability, are known to provide rates which are too slow to explain the observations. However, a recent analysis has shown that there exists a critical threshold on current sheet's thickness, namely a/L ∼ S -1/3, beyond which the tearing modes evolve on fast macroscopic Alfvénic timescales, provided the Lunquist number S is high enough, as invariably found in solar and astrophysical plasmas. Therefore, the classical Sweet-Parker scenario, for which the diffusive region scales as a/L ∼ S -1/2 and thus can be up to ∼ 100 times thinner than the critical value, is likely to be never realized in nature, as the current sheet itself disrupts in the elongation process. We present here two-dimensional, compressible, resistive MHD simulations, with S ranging from 105 to 107, that fully confirm the linear analysis. Moreover, we show that a secondary plasmoid instability always occurs when the same critical scaling is reached on the local, smaller scale, leading to a cascading explosive process, reminiscent of the flaring activity.
- Publication:
-
Journal of Physics Conference Series
- Pub Date:
- May 2016
- DOI:
- 10.1088/1742-6596/719/1/012016
- arXiv:
- arXiv:1603.04995
- Bibcode:
- 2016JPhCS.719a2016D
- Keywords:
-
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Proceedings of ASTRONUM 2015, Avignon, France (11 pages, 6 figures)