Magnetic reconnection with null and X-points

Journal Article · 02 December 2019 · Physics of Plasmas

DOI: https://doi.org/10.1063/1.5121320 · OSTI ID:1800136

Boozer, Allen H.  ^[1]

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1. Columbia Univ., New York, NY (United States); Columbia University

Null and X-points are not themselves directly important to magnetic reconnection because distinguishable field lines do not approach them closely. Even in a collision-free plasma, magnetic field lines that approach each other on a scale c/$$\omega_\rho$$_e become indistinguishable during an evolution. What is important is the different regions of space that can be explored by magnetic field lines that pass in the vicinity of null and X-points. Traditional reconnection theories made the assumption that the reconnected magnetic flux must be dissipated or diffused by an electric field. This assumption is false in three dimensional systems because an ideal evolution can cause magnetic field lines that cover a large volume to approach each other within the indistinguishability scale c/$$\omega_\rho$$_e. When the electron-ion collision time τei is short compared to the evolution time of the magnetic field τev, the importance of c/$$\omega_\rho$$_e is replaced by the resistive time scale $$\tau$$$$_\eta$$=($$\eta$$/$$\mu$$₀)L² with L being the system scale. The magnetic Reynolds number R_m≡$$\tau$$$$\eta$$/$$\tau$$_e$$_\nu$$ is enormous in many reconnection problems of interest. Magnetic flux diffusion implies the current density required for reconnection to compete with evolution scales as Rm, while flux mixing implies the required current density to compete scales as ln R_m.

• Research Organization: Columbia Univ., New York, NY (United States); Columbia University, New York, NY (United States)
• Sponsoring Organization: Department of Energy; USDOE; USDOE Office of Science (SC); USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: FG02-03ER54696; FG02-95ER54333; SC0018424; SC0019479
• OSTI ID: 1800136
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 26; ISSN 1070-664X
• Publisher: American Institute of Physics (AIP)Copyright Statement
• Country of Publication: United States
• Language: English