Strongly localized magnetic reconnection by the super-Alfvénic shear flow

Area of Science:

• Plasma Physics
• Astrophysics
• Space Physics

Background:

• Magnetic reconnection is a fundamental process in plasma physics, crucial for energy release in astrophysical and laboratory plasmas.
• Previous models, often based on resistive magnetohydrodynamics, struggle to explain fast reconnection rates observed in collisionless plasmas.

Purpose of the Study:

• To investigate the role of super-Alfvénic shear flows in localizing the magnetic reconnection x-line in collisionless pair plasmas.
• To understand the underlying mechanisms enabling reconnection with a novel morphology and its impact on the reconnection rate.

Main Methods:

• Numerical simulations of collisionless pair plasmas.
• Analysis of magnetic field advection, particle inertia effects, and x-line geometry.
• Examination of magnetic flux transport and upstream magnetic field opening angles.

Main Results:

• Super-Alfvénic shear flows drive magnetic field lines out of the reconnection plane, strongly localizing the x-line and reversing current direction.
• Particle inertia enables this unique reconnection morphology, which is not possible in resistive magnetohydrodynamics.
• A quasi-steady reconnection rate of approximately 0.1 is maintained despite an x-line aspect ratio greater than unity, excluding tearing physics.

Conclusions:

• The observed fast reconnection rate is limited by upstream inflow constraints, not solely by the localization mechanism or dissipation.
• The reconnection rate of ~0.1 is likely an upper bound, generally determined by upstream conditions, irrespective of specific localization or dissipation processes.
• This study reveals a new mechanism for fast magnetic reconnection in collisionless plasmas, with implications for understanding energetic events in space and astrophysics.