Laboratory study of ion and electron dynamics during asymmetric magnetic reconnection

Abstract:

Magnetic reconnection at the dayside magnetopause has a large density asymmetry across the current sheet. To study effects of the density asymmetry on the ion and electron dynamics, plasmas with a significant (~10) density asymmetry are created in the Magnetic Reconnection Experiment (MRX) [1]. The density asymmetry affects the ion flow pattern by changing the in-plane electrostatic field such that the potential decrease on the high-density side becomes much smaller than that on the low-density side [2]. The ion inflow stagnation point is shifted toward the low-density side and the maximum ion outflow velocity is observed on the low-density side. The density asymmetry also makes the electron temperature profile asymmetric, which has a higher temperature near the low-density-side separatrices. The bulk electron heating is proportional to the total incoming magnetic energy per particle. The electron energization process during asymmetric reconnection is studied via numerical simulations. By comparing 2D simulations with corresponding 3D simulations, we find that the overall energization process does not depend on variations along the third dimension. Where and how electrons are energized during asymmetric reconnection will be discussed by using data from 2D numerical simulations. Finally, the scaling of the reconnection rate and the ion outflow speed given by the Cassak and Shay 2007 [3] is tested by systematically varying the density ratio. The measured ion outflow speed is about 40% of the theoretical values and the measured reconnection rate agrees with the scaling only with the measured density in the exhaust region.

[1] M. Yamada  et al., Phys. Plasmas 4, 1936 (1997).

[2] J. Yoo et al., Phys. Rev. Lett. 113, 095002 (2014).

[3] P. Cassak and M. Shay, Phys. Plasmas 14, 102114 (2007).