Nonlinear evolution of the lower hybrid drift instability: Current sheet thinning and kinking

Through numerical plasma simulations using the implicit code CELESTE3D [G. Lapenta and J. U. Brackbill, Nonlinear Processes Geophys. 7, 151 (2000)], the development of kink modes in a Harris current sheet is investigated, and their possible nonlinear interaction with the lower hybrid drift instability (LHDI) is considered. Consistent with earlier work, the rapid development of a short wavelength LHDI is observed, followed by the slow development of long wavelength current sheet kinking. The growth of kink modes is in agreement with the linear theory for the drift kink instability only at very small mass ratios (mi/me=16). At more realistic mass ratios, the growth rate exceeds that predicted by linear theory. A thorough investigation of the dependence of current sheet kinking on ion/electron mass and temperature ratios, and current sheet thickness reveals that the growth of kink modes is unaffected by current sheet thinning, but is strongly dependent on the ion/electron temperature ratio. The saturation amplitude of the LHDI increases with decreasing electron temperature, as do the nonlinear modifications of the initial equilibrium. In particular, the ion diamagnetic drift velocity of the ions decreases sufficiently on the flanks of the current sheet to support a Kelvin-Helmholtz instability, especially with cold electrons, whose properties are completely consistent with the kink modes observed in the simulations