Authors: Tak Chu Li (Dartmouth College), Yi-Hsin Liu (Dartmouth College), and Yi Qi (University of Colorado Boulder)

Electron-only magnetic reconnection was first identified by the Magnetospheric Multiscale (MMS) mission in Earth’s magnetosheath turbulence and reported to be prevalent in subion-scale turbulence. The prevalence of electron-only reconnection could have implications for plasma heating and particle acceleration in the solar wind and solar corona flare plasmas. Subsequent observational and simulation studies reveal the challenge in identifying electron-only magnetic reconnection due to the absence of the more accessible ion signatures. The magnetic flux transport (MFT) method is an innovative method that considers the transport of magnetic flux around reconnection X-lines to identify active reconnection in numerical simulations and in situ observations. Here we extend the capability of the MFT method to distinguish between electron-only and ion-coupled reconnection. The coupling of magnetic field motion with ion and electron flows in the diffusion regions sets different scales in the MFT velocity for the two forms of reconnection. Both forms of reconnection satisfy the standard MFT signature for active reconnection. The specific electron-only signature is an electron-scale MFT outflow along the inflow direction. The specific ion-coupled signature is an inner-electron- and outer-ion-scale MFT outflow, or an ion-scale MFT outflow, in the inflow direction. These specific signatures are investigated in a simulation of gyrokinetic turbulence. The dependence of the MFT outflow on the distance downstream from the reconnection X-line agrees with the result of the coupling of the magnetic field motion with ion and electron flows. In ion-coupled reconnection, the specific signature evolves from a two-scale to a single ion-scale MFT outflow when transitioning from the electron diffusion region (EDR) into the ion diffusion region (IDR). In electron-only reconnection, the specific signature remains robust downstream from the X-line, until the X-line terminates. These distinct MFT signatures of the two forms of reconnection can provide a simple and accurate identification of reconnection in complex plasmas.