3-D Gyrokinetic Electron and Fully Kinetic Ion Simulation of Current Sheet Instabilities

Instability of a Harris current sheet is investigated using a 3-D linearized ($\delta{f}$) electromagnetic gyrokinetic electron and fully kinetic ion (GeFi) particle simulation code. The equilibrium magnetic field consists of an asymptotic anti-parallel component $B_{x0}$ and a guide field $B_G$, with the current sheet normal in the $z$ direction. The simulation is performed for cases with a broad range of $B_G$. The eigenmode structure, real frequency, and the growth rate of instabilities are calculated as a function of wave numbers $k_{x}$ and $k_{y}$. In the cases with a small $k_{y}\rho_{e}$, tearing mode is found to dominate, with peak growth rate at $k_{x}L = 0.4$-0.5, where $L$ is the half-width of the current sheet. On the other hand, in the cases with a small $k_{x}\rho_{e}\leq 0.1$, there exist two unstable modes: a quasi-electrostatic mode at the current sheet edge with wave number $0.3\leq k_{y}\rho_{e}\leq 0.6$ and frequency around the lower-hybrid frequency $\omega_{LH}$ and an electromagnetic mode with $k_{y}\rho_{e}\leq 0.2$ at the sheet center under a guide field $B_G/B_{x0}=0.1$. The transition from the tearing-like instability to the $k_y$-dominant instabilities is presented by scanning through the $(k_x, k_y)$ space. The complete 3-D profile of instabilitie