Modeling the "Electron-Only" magnetic reconnection rates at sub-ion-scales

"Electron-only" reconnection, which is both uncoupled from the surrounding ions and much faster than standard reconnection, is arguably ubiquitous in turbulence. One critical step in understanding the rate in this novel regime is to model the outflow speed that limits the transport of magnetic flux, which is super-ion Alfvénic but significantly lower than the electron Alfvén speed based on the asymptotic reconnecting field. In this talk, I will present a simple model to determine the limiting speed by taking into account the multiscale nature of reconnection, the Hall-mediated electron outflow speed, and the pressure buildup within the small system. The predicted scalings of rates and various key quantities compare well with fully kinetic simulations. They can help interpret observations from NASA's Magnetospheric Multiscale (MMS) mission and small-scale reconnection in laboratory experiments.