Scaling theory of three-dimensional magnetic reconnection spreading

Journal Article · Mon Aug 02 00:00:00 UTC 2021 · Physics of Plasmas

DOI: https://doi.org/10.1063/5.0052189 · OSTI ID:1853560

Arencibia, Milton  ^[1]; Cassak, P. A.  ^[2]; Shay, M. A.  ^[3]; Priest, E. R.  ^[4]

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1. West Virginia University, Morgantown, WV (United States); West Virginia Univ., Morgantown, WV (United States)
2. West Virginia University, Morgantown, WV (United States)
3. University of Delaware, Newark, DE (United States)
4. University of St. Andrews, Scotland (United Kingdom)

We develop a first-principles scaling theory of the spreading of three-dimensional (3D) magnetic reconnection of finite extent in the out of plane direction. This theory addresses systems with or without an out of plane (guide) magnetic field, and with or without Hall physics. The theory reproduces known spreading speeds and directions with and without guide fields, unifying previous knowledge in a single theory. New results include: (1) Reconnection spreads in a particular direction if an x-line is induced at the interface between reconnecting and non-reconnecting regions, which is controlled by the out of plane gradient of the electric field in the outflow direction. (2) The spreading mechanism for anti-parallel collisionless reconnection is convection, as is known, but for guide field reconnection it is magnetic field bending. We confirm the theory using 3D two-fluid and resistive-magnetohydrodynamics simulations. (3) The theory explains why anti-parallel reconnection in resistive-magnetohydrodynamics does not spread. (4) The simulation domain aspect ratio, associated with the free magnetic energy, influences whether reconnection spreads or convects with a fixed x-line length. (5) We perform a simulation initiating anti-parallel collisionless reconnection with a pressure pulse instead of a magnetic perturbation, finding spreading is unchanged rather than spreading at the magnetosonic speed as previously suggested. The results provide a theoretical framework for understanding spreading beyond systems studied here, and are important for applications including two-ribbon solar flares and reconnection in Earth’s magnetosphere.

• Research Organization: University of California, Oakland, CA (United States); West Virginia University, Morgantown, WV (United States)
• Sponsoring Organization: National Aeronautics and Space Administration (NASA); National Science Foundation (NSF); USDOE Office of Science (SC)
• Grant/Contract Number: AC02-05CH11231; SC0020294
• OSTI ID: 1853560
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 8 Vol. 28; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English