Abstract Details
| status: | file name: | submitted: | by: |
|---|---|---|---|
| approved | b_evolution_feb2023_arxiv.pdf | 2023-03-14 10:09:20 | Allen Boozer |
Abstracts
Author: Allen H Boozer
Requested Type: Consider for Invited
Submitted: 2023-03-14 10:07:39
Co-authors: T. Elder
Contact Info:
Columbia University
128 Jerdone Road
Williamsburg, VA 23185
USA
Abstract Text:
Magnetic field evolution has three aspects: (1) changes in field line connections, (2) transfer of magnetic to plasma energy, (3) and conservation of magnetic helicity, https://arxiv.org/pdf/2212.07487.pdf>. Magnetic field lines are chaotic when within in a non-zero volume neighboring lines increase their separation through many e-folds with distance along the lines while remaining in a bounded region perpendicular to the field. Magnetic chaos has an essential role, but requires three spatial coordinates: Magnetic field lines can go from a simple smooth form to having large and broadly-spread changes in their connections on a timescale that is approximately a factor of ten longer than the ideal evolution time when and only when the magnetic field lines become chaotic. When the number of e-folds exceeds the magnetic Reynolds number, tubes of magnetic field lines become so contorted that resistive diffusion intermixes lines from different tubes. An ideal magnetic evolution can change non-chaotic into chaotic lines with an arbitrarily large of number of e-folds. In coronal loops, magnetic field lines evolve due to chaotic footpoint flows. A two-dimensional flow is chaotic when neighboring streamlines e-fold apart in time. This forces a temporal increase in the e-folds of separation between neighboring magnetic field lines as they traverse a coronal loop. More subtly, ideal magnetic perturbations of sufficient amplitude can cause the separation between neighboring toroidal magnetic surfaces to vary exponentially over the surfaces. Chaos allows an ideal evolution to lead to a sudden loss of field line connections, which releases energy from the magnetic field when the current density is too low to provide resistive damping. The result is Alfvén waves, which cause the rapid development of the current and vorticity sheets required for damping. The whole evolution is controlled by helicity conservation, which can force coronal-loop eruption.
Comments: