Abstract
A two-dimensional three-component (2D/3C) electron magnetohydrodynamic (EMHD) model is implemented to investigate the linear behavior of collisionless tearing modes in slab geometry. Owing to nonuniformity of thermal pressure and plasma density, the electron diamagnetic drift and Biermann battery effects are involved. The linear structures, growth rate, and real frequency are analyzed with a thin current sheet in the electron inertia scale. The ratio of the electron current to the total current in equilibrium can notably promote the growth of the tearing mode in EMHD. More numerical results then show that the effect of the pressure gradient on the tearing mode is dependent on the plasma beta, stabilizing the mode in a low enough beta limit but destabilizing it with the higher beta. The frequency of the mode caused by the pressure gradient is found to be increasing with it. The Biermann battery effect slightly stabilizes the tearing mode in low beta plasma but is indicated to be significant in much higher beta conditions.
Highlights
The tearing mode is one of the most important magnetohydrodynamic (MHD) instabilities in magnetized plasma, which is identified as unsteady state magnetic reconnection driven by free energy stored in plasma.[1,2,3] The reconnection process can convert the magnetic energy to the kinetic energy as Alfvénic outflows and thermal energy
We can find that the inertial terms on the right-hand side (RHS) of Eqs. (20) and
As to the effect on the growth of the tearing mode, we find the pressure gradient enhances the growth rate of the electron magnetohydrodynamic (EMHD) tearing mode, contrary to that in the MHD model but consistent with that in EMHD theory
Summary
The tearing mode is one of the most important magnetohydrodynamic (MHD) instabilities in magnetized plasma, which is identified as unsteady state magnetic reconnection driven by free energy stored in plasma.[1,2,3] The reconnection process can convert the magnetic energy to the kinetic energy as Alfvénic outflows and thermal energy. In scales smaller than ion inertial length, the other non-collisional effects such as the finite electron inertia effect and/or Hall effects in the generalized Ohm’s law (1) can dominate the reconnection process of magnetic field and lead to the collisionless reconnection.[12–18]. This equation is normalized by the typical values of the thermal pressure p, plasma density n, and magnetic field B, as well as√the typical length scale a and the Alfvén time τA = a/vA with vA = B/ 4πnmi. The numerical algorithm and diagnostic methods applied in our code are briefly explained in Appendix A, and code verification is in Appendix B
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