Phase-space contributions to pressure and stress tensors in the electron diffusion region of magnetic reconnection

Magnetic reconnection is a fundamental plasma process in collisionless plasma that governs the transfer of magnetic energy to plasma energy through a change in magnetic topology. The reconnection electric field, or equivalently, the rate at which the magnetic flux is reconnected, must everywhere satisfy momentum balance. In this study, using in situ spacecraft measurements from the Magnetospheric MultiScale mission, supported by test-particle simulations and kinetic particle-in-cell simulations, we investigate how various electron populations contribute to the reconnection electric field inside the electron diffusion region by supplying or diverting momentum away from the X line. We show that the electron pressure anisotropy that develops in the inflow reduces the reconnection electric field by transporting momentum toward the X line. A net outward flux of momentum in the direction normal to the current sheet likely contributes positively to the reconnection electric field.