Nuclear and Atomic Physics

Magnetic Moment Force and Semi-Free Electrons: a First-Principles Model for Fast Magnetic Reconnection

Authors: Yuanjie Huang
Comments: 29 Pages.

A long-standing puzzle in plasma physics is the universally fast rate of magnetic reconnection, observed to be of order 0.1 across diverse environments yet unexplained by classical resistive magnetohydrodynamics (MHD). We propose a new analytical model for two-dimensional steady-state reconnection based on two concepts: the magnetic moment force as the gyro-averaged Lorentz force, and the semi-free electron constraint arising from quasi-neutrality. We show that the inflow is driven by the magnetic moment force rather than resistive diffusion, while the outflow is governed by the ion pressure gradient. The model yields a closed-form reconnection rate that depends only on the electron-to-ion temperature ratio and ion charge state, independent of system size, field strength, density, and resistivity. For a thermal equilibrium hydrogen plasma, the rate is approximately 0.2, consistent with satellite observations and simulations. The model also reproduces the bipolar electrostatic field at the current sheet center. Compared with Sweet-Parker, Petschek, and Hall-MHD models, our framework offers a first-principles kinetic explanation for the universal reconnection rate. Finally, we propose a corresponding modification to the two-fluid MHD equations, removing the electron pressure gradient and replacing the Lorentz force with the magnetic moment force.
Category: Nuclear and Atomic Physics