Electron Backflow Motions in the Outer Electron Diffusion Region During Magnetic Reconnection

Magnetic reconnection is a fundamental physical process of rapidly converting magnetic energy into particles. The electron diffusion region (EDR) is the crucial region during magnetic reconnection. The outer EDR, which also plays a crucial role in magnetic reconnection, is responsible for energy conversion. In the outer EDR, the electrons are decelerated and return the energy to the magnetic field on the pileup region behind the reconnection front. In the present study, we used the fully kinetic particle-in-cell simulation and revealed that part of decelerated electrons in the outer EDR could even move back to the inner EDR. This phenomenon is caused by the dominant contribution from the magnetic tension force, and it suggests a magnetic Marangoni effect in space plasma, similar to the Marangoni effect in fluids. Our results potentially propose a brand-new physical process and a novel mechanism in the EDR during magnetic reconnection. Plasma's energy can be changed through various approaches in the universe, and magnetic reconnection is one of those approaches to convert energy from the magnetic field to the plasma. In the reconnection site, the inner electron diffusion region (EDR) is an essential area where the energy is released, and the electron's energy is enhanced significantly. Meanwhile, in the outer EDR, the electrons are decelerated by the electric field, thus their energy decreases. However, part of those electrons can move backward to the inner EDR, and how this phenomenon comes up has no further investigation. In this study, we use numerical simulations to reveal the possible mechanism of this kind of electron's motion. It is found that the electron deceleration is caused by the magnetic tensor force. The electrons with specific conditions have the possibility to move backward. Those backflow electrons have a second chance to be accelerated again in the inner EDR. Such electron motion in plasma physics is not a kind of gyro movement but might indicate a so-called magnetic Marangoni effect similar to the Marangoni effect in fluid physics. Our findings propose a novel mechanism associated with electron acceleration in the EDR during magnetic reconnection. The magnetic tension force causes the deceleration of the electrons in the outer electron diffusion region (EDR) during magnetic reconnectionPartial electrons are decelerated and even move back to the inner EDR, and they are accelerated again and attain higher energyThe electron backflow motion in the outer EDR indicates a magnetic Marangoni effect in space plasma

Automated summary

Magnetic reconnection is a fundamental process that converts magnetic energy into particles. The electron diffusion region (EDR) plays a crucial role in this process. In this study, it is revealed through simulations that part of the decelerated electrons in the outer EDR can even move back to the inner EDR, suggesting a magnetic Marangoni effect in space plasma. This finding introduces a novel mechanism in the EDR during magnetic reconnection.