An improved gyrokinetic electron and fully kinetic ion (GeFi) particle simulation scheme is presented for the investigation of linear collisionless tearing mode instability in a two-dimensional Harris current sheet under a finite guide field B G and a realistic ion-to-electron mass ratio m i /m e . Due to the removal of the rapid electron cyclotron motion while retaining the finite electron Larmor radii, wave-particle interaction, and off-diagonal components of the electron pressure tensor, the GeFi model can be used to investigate the physics of magnetic reconnection with a realistic m i /m e in a large-scale current sheet, which in general possesses wave modes ranging from Alfvén waves to lower hybrid/whistler waves, with wave frequency ω < e , where e is the electron gyrofrequency. As a necessary step of utilizing the code for magnetic reconnection, the linearized GeFi scheme is benchmarked by comparing the simulation results using a δf method against direct numerical solutions of the tearing-instability eigenmode equations, as well as those obtained analytically via asymptotic matching.

We have developed a new gyrokinetic (GK) electron and fully kinetic ion (GeFi) particle simulation scheme using electric field E and magnetic field B directly as field variables. Corresponding nonlinear GK equations in terms of E and B are also derived. This new GeFi-E&B scheme is applicable for simulating plasma dynamics covering a broad frequency range and using a realistic electron-to-ion mass ratio. Simulation results are successfully benchmarked against analytical theories.