The Effect of Ion Gyroradius in the Transition from Electron-only to Ion-coupled Reconnection

Abstract

<p>    Electron-only magnetic reconnection, which occurs without ion coupling, has recently been observed in both magnetosheath and magnetotail. A previous simulation study using conditions in magnetosheath shows that obtaining electron-only reconnection needs a small enough simulation domain whose length is smaller than 10d<sub>i</sub>. In this work, using 2.5-D PIC simulations, we find that the degree of ion coupling in magnetic reconnection is also adjusted by the ion gyroradius R<sub>ci</sub>. The electron-only reconnection occurs when the size of the simulation domain is less than about 2R<sub>ci</sub>. In this case, the motion of the ions is dominated by cyclotron motion, and most of the ions go through the region where the reconnection electric field exists too quickly to be accelerated, so the ion outflow and the ion current sheet do not appear. Without changing the size of simulation domains, as the ion temperature decreases, the ion gyroradius decreases, and ions gradually respond to the reconnection.</p>