Electron-only reconnection and inverse magnetic-energy transfer at sub-ion scales*

Electron-only reconnection is a type of magnetic reconnection occurring in sufficiently small regions where ions remain unresponsive to reconnection dynamics. In this work, we derive, and validate numerically, an analytical model for electron-only magnetic reconnection applicable to strongly magnetized (low-beta) plasmas. Our model predicts sub-ion-scale reconnection rates significantly higher than those pertaining to MHD scale reconnection, aligning with recent observations and simulations. We then apply this reconnection model to the problem of inverse magnetic-energy transfer at sub-ion scales. We derive time-dependent scaling laws for the magnetic energy decay that differ from those previously found in the MHD regime. These scaling laws are validated via two- and three-dimensional simulations, demonstrating that sub-ion scale magnetic fields can reach large, system-size scales via successive coalescence. The properties of the associated plasma turbulence, including the energy spectrum and typical magnetic structure dimensions are investigated.