The structure of the electron outflow jet in collisionless magnetic reconnection

Particle-in-cell simulations and analytic theory are applied to the study of the electron outflow jet in collisionless magnetic reconnection. In these jets, which have also been identified in spacecraft observations, electron flow speeds in thin layers exceed the E ×B drift, suggesting that electrons are unmagnetized. In this study, we find the surprising result that the electron flow jets can be explained by a combination of E ×B drifts and of diamagnetic effects through the combination of the gradients of particle pressure and of the magnetic field. In a suitably rotated coordinate system, the electron motion is readily decomposed into E ×B drift and the motion to support the required current density, consistent with electron gyrotropy. This process appears to be nondissipative.