Magnetic nulls in interacting dipolar fields

Abstract

The prominence of nulls in reconnection theory is due to the expected singular current density and the indeterminacy of field-lines at a magnetic null. Electron inertia changes the implications of both features. Magnetic field lines are distinguishable only when their distance of closest approach exceeds a distance ${\Delta }_d$. Electron inertia ensures ${\Delta }_d\gtrsim c/{\omega }_{pe}$. The lines that lie within a magnetic flux tube of radius ${\Delta }_d$ at the place where the field strength $B$ is strongest are fundamentally indistinguishable. If the tube, somewhere along its length, encloses a point where $B=0$,vanishes, then distinguishable lines come no closer to the null than $\approx (a^{2}c/{\omega }_{pe}{)}^{1/3}$, where $a$ is a characteristic spatial scale of the magnetic field. The behavior of the magnetic field lines in the presence of nulls is studied for a dipole embedded in a spatially constant magnetic field. In addition to the implications of distinguishability, a constraint on the current density at a null is obtained, and the time required for thin current sheets to arise is derived.

References in corpus (5)

• In situ evidence for the structure of the magnetic null in a 3D reconnection event in the Earth's magnetotail
• Current Singularities at Quasi-Separatrix Layers and Three-Dimensional Magnetic Nulls
• Particle acceleration and fast magnetic reconnection
• Magnetic reconnection and thermal equilibration
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Cited by in corpus (4)

• Magnetic reconnection and thermal equilibration
• Example of exponentially enhanced magnetic reconnection driven by a spatially-bounded and laminar ideal flow
• Magnetic field evolution and reconnection in low resistivity plasmas
• Local analysis of fast magnetic reconnection