Investigation of Current Sheet Instabilities Using a GKE/FKI Particle Simulation Model

The instability of current sheet under finite guide field ($B_y$) is investigated using our new gyrokinetic (GK) electron and fully kinetic (FK) ion particle simulation code, which resolves wave modes ranging from Alfv\'en waves to lower-hybrid/whistler waves. Compared with full-particle codes, the rapid electron cyclotron motion is removed in this model, while the realistic mass ratio $m_e/m_i$, finite electron Larmor radii, and wave-particle interactions are kept. The computation power is significantly improved. The preliminary simulation of Harris sheet is carried out in the 2D $yz$ plane, with $z$ being along the current sheet normal and anti-parallel $B_x$ perpendicular to the simulation plane. The simulation has been performed with both a linearized ($\delta f$) GKe/FKi code and the nonlinear code, for $B_y/B_x=0.1$-$10$. Under very small $B_y$, our results show LHDI modes at the current sheet edge propagating mainly in the $y$ direction, as seen in previous simulations. As $B_y$ increases, $k_\perp$ and diamagnetic drift direction shift away from the current flow direction $y$. The LHDI modes become weaker while high frequency modes stronger. In the cases with a large $B_y$, the LHDI modes evolve to a globally propagating instability, and multiple ion cyclotron modes are excited. A more complete 3D simulation is planned to investigate the new physics introduced by the large guide field.