GeFi Simulation of Electron-Ion Hybrid Instability

Shear flow instabilities play an important role in laboratory as well as space plasmas. Excitation of the electron-ion hybrid (EIH) instability in a magnetized plasma with a transverse electric field and thus a localized electron cross-field flow is investigated using our gyrokinetic electron and fully-kinetic ion (GeFi) particle simulation model. Regime with $\rho _{\mathrm{e}}$\textless L$_{\mathrm{E}}$ \textless $\rho_{\mathrm{i}}$ is considered, where $\rho_{\mathrm{i}}$ and $\rho_{\mathrm{e}}$ are the electron and ion Larmor radii, respectively, and L$_{\mathrm{E}}$ represents the scale length of the shear flow profile. Both linear and nonlinear physics are studied. First, for the shear flow profile in a slab geometry, the simulation model is benchmarked by comparison of the eigen mode structure obtained from the linear GeFi results in a uniform plasma density with that from the linear theory [e.g., Ganguli, Lee, and Palmadesso, 1987], and good agreement is obtained. Vortex-like structures are also observed in the electrostatic potential. Second, in the nonlinear GeFi simulation, the EIH mode instability saturates in a time scale t$=$0.2/$\Omega_{\mathrm{i}}$ ($\Omega_{\mathrm{i}}$ is the ion gyrofrequency), and it nonlinearly evolves to a lower hybrid mode. Third, linear and nonlinear EIH instabilities in a plasma with a nonuniform density is also simulated. Finally, the GeFi simulation is carried out in a cylindrical geometry for conditions of the Auburn Linear Experiment for Instability Studies (ALEXIS) experiment. The results are compared with the ALEXIS measurements of the EIH instability.