3-D Electromagnetic Instabilities in Current Sheet

3-D electromagnetic instabilities in a Harris current sheet with a finite guide magnetic field $B_{G}$ are systematically studied by employing the gyrokinetic electron and fully kinetic ion (GeFi) particle model with a realistic mass ratio $m_i/m_e$. Our studies show that lower-hybrid drift instability (LHDI) with $k\sqrt{\rho_i\rho_e} \sim 1$ and drift kink instability (DKI) and drift sausage instability (DSI) with $k\rho_i \sim 1$ are excited in the current sheet. The most unstable DKI is away from $\mathbf{k} \cdot \mathbf{B}=0$, and the most unstable DSI is at $\mathbf{k} \cdot \mathbf{B}=0$, where $\mathbf{k} \equiv (k_x, k_y)$, with $k_x$ being along the anti-parallel field direction and $k_y$ is along the current direction. On the other hand, an instability with a compressional magnetic field perturbation located at the center of current sheet is also excited under a relatively large $B_G$, and its maximum growth rate is at $\mathbf{k} \times \mathbf{B} = 0$. The presence and structure of these instabilities as a function of $B_G$ is presented. The GeFi simulation results are compared with those from the fully kinetic particle simulation.