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Title: Rapid change of field line connectivity and reconnection in stochastic magnetic fields

Abstract

Magnetic fields without a direction of continuous symmetry have the generic feature that neighboring field lines exponentiate away from each other and become stochastic, and hence the ideal constraint of preserving magnetic field line connectivity becomes exponentially sensitive to small deviations from ideal Ohm's law. The idea of breaking field line connectivity by stochasticity as a mechanism for fast reconnection is tested with numerical simulations based on reduced magnetohydrodynamics equations with a strong guide field line-tied to two perfectly conducting end plates. Starting from an ideally stable force-free equilibrium, the system is allowed to undergo resistive relaxation. Two distinct phases are found in the process of resistive relaxation. During the quasi-static phase, rapid change of field line connectivity and strong induced flow are found in regions of high field line exponentiation. However, although the field line connectivity of individual field lines can change rapidly, the overall pattern of field line mapping appears to deform gradually. From this perspective, field line exponentiation appears to cause enhanced diffusion rather than reconnection. In some cases, resistive quasi-static evolution can cause the ideally stable initial equilibrium to cross a stability threshold, leading to formation of intense current filaments and rapid change of field linemore » mapping into a qualitatively different pattern. It is in this onset phase that the change of field line connectivity is more appropriately designated as magnetic reconnection. Our results show that rapid change of field line connectivity appears to be a necessary, but not a sufficient condition for fast reconnection.« less

Authors:
;  [1]
  1. Department of Astrophysical Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, NJ 08543 (United States)
Publication Date:
OSTI Identifier:
22370560
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 793; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COMPUTERIZED SIMULATION; DIFFUSION; EQUATIONS; EQUILIBRIUM; EVOLUTION; MAGNETIC FIELDS; MAGNETIC RECONNECTION; MAGNETOHYDRODYNAMICS; MAPPING; PLASMA; RELAXATION; STABILITY; STOCHASTIC PROCESSES; SUN; SYMMETRY

Citation Formats

Huang, Yi-Min, Bhattacharjee, A., and Boozer, Allen H., E-mail: yiminh@princeton.edu. Rapid change of field line connectivity and reconnection in stochastic magnetic fields. United States: N. p., 2014. Web. doi:10.1088/0004-637X/793/2/106.
Huang, Yi-Min, Bhattacharjee, A., & Boozer, Allen H., E-mail: yiminh@princeton.edu. Rapid change of field line connectivity and reconnection in stochastic magnetic fields. United States. https://doi.org/10.1088/0004-637X/793/2/106
Huang, Yi-Min, Bhattacharjee, A., and Boozer, Allen H., E-mail: yiminh@princeton.edu. 2014. "Rapid change of field line connectivity and reconnection in stochastic magnetic fields". United States. https://doi.org/10.1088/0004-637X/793/2/106.
@article{osti_22370560,
title = {Rapid change of field line connectivity and reconnection in stochastic magnetic fields},
author = {Huang, Yi-Min and Bhattacharjee, A. and Boozer, Allen H., E-mail: yiminh@princeton.edu},
abstractNote = {Magnetic fields without a direction of continuous symmetry have the generic feature that neighboring field lines exponentiate away from each other and become stochastic, and hence the ideal constraint of preserving magnetic field line connectivity becomes exponentially sensitive to small deviations from ideal Ohm's law. The idea of breaking field line connectivity by stochasticity as a mechanism for fast reconnection is tested with numerical simulations based on reduced magnetohydrodynamics equations with a strong guide field line-tied to two perfectly conducting end plates. Starting from an ideally stable force-free equilibrium, the system is allowed to undergo resistive relaxation. Two distinct phases are found in the process of resistive relaxation. During the quasi-static phase, rapid change of field line connectivity and strong induced flow are found in regions of high field line exponentiation. However, although the field line connectivity of individual field lines can change rapidly, the overall pattern of field line mapping appears to deform gradually. From this perspective, field line exponentiation appears to cause enhanced diffusion rather than reconnection. In some cases, resistive quasi-static evolution can cause the ideally stable initial equilibrium to cross a stability threshold, leading to formation of intense current filaments and rapid change of field line mapping into a qualitatively different pattern. It is in this onset phase that the change of field line connectivity is more appropriately designated as magnetic reconnection. Our results show that rapid change of field line connectivity appears to be a necessary, but not a sufficient condition for fast reconnection.},
doi = {10.1088/0004-637X/793/2/106},
url = {https://www.osti.gov/biblio/22370560}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 793,
place = {United States},
year = {Wed Oct 01 00:00:00 EDT 2014},
month = {Wed Oct 01 00:00:00 EDT 2014}
}