Current-sheet kink instability at ion-electron hybrid scale

Current sheet instabilities having wavenumber vectors parallel to the current direction are studied as a linear eigenvalue problem in a two-fluid system where electrons are treated as a finite-mass charge neutralizing component. Focusing on ion-scale current sheets, we show that a hybrid scale current sheet kink instability (CSKI) is one of the major instabilities to appear. The hybrid scale CSKI in a magnetotail-like situation has a wavelength much shorter than the well-studied drift-kink instability (DKI). While most of the previous studies have focused on the long-wavelength range, a full-particle simulation with much larger ion-to-electron mass ratio (R_M = 400) shows the growth of the hybrid scale CSKI as predicted by linear analyses. We also show that the CSKI has large growth rates in a magnetopause-like situation.