3-D Particle Simulation of Current Sheet Instabilities

The electrostatic (ES) and electromagnetic (EM) instabilities of a Harris current sheet are investigated using a 3-D linearized ($\delta{f}$) gyrokinetic (GK) electron and fully kinetic (FK) ion (GeFi) particle simulation code. The equilibrium magnetic field consists of an asymptotic anti-parallel $B_{x0}$ and a guide field $B_G$. The ES simulations show the excitation of lower-hybrid drift instability (LHDI) at the current sheet edge. The growth rate of the 3-D LHDI is scanned through the $ (k_x, k_y)$ space. The most unstable modes are found to be at $k_{\parallel}=0$ for smaller $k_y$. As $k_y$ increases, the growth rate shows two peaks at $k_{\parallel} \not =0$, consistent with analytical GK theory. The eigenmode structure and growth rate of LHDI obtained from the GeFi simulation agree well with those obtained from the FK PIC simulation. Decreasing $B_G$, the asymptotic $\beta_{e0}$, or background density can destabilize the LHDI. In the EM simulation, tearing mode instability is dominant in the cases with $k_{y} < k_{x}$. For $k_{y} > k_{x}$, there exist two unstable modes: a kink-like (LHDI) mode at the current sheet edge and a sausage-like mode at the sheet center. The results are compared with the GK eigenmode theory and the FK simulation.