Drift ballooning mode in a kinetic model of the near-Earth plasma sheet

In the near-Earth plasma sheet the pressure gradient and magnetic curvature are both directed earthward. This region is thus potentially unstable to the ballooning mode provided that the plasma beta becomes large enough. In this work a three-dimensional electromagnetic full-particle simulation is used to study the evolution of the near-Earth plasma sheet under the influence of an external convection electric field. As the plasma beta increases to similar to 10 during the convection process, the excitation of a drift ballooning mode is observed whose real frequency and growth rate agree well with fluid predictions including the effect of the ion diamagnetic drift. The maximum intensity in the ballooning spectrum corresponds to an azimuthal mode number m similar to 60. The spectrum is observed to evolve toward shorter wavelengths, but this process stops at the ion gyroradius scale. There is no sign of an explosive nonlinear stage of the instability. The bulk flows produced by the mode are only moderate (less than or similar to 200 km/s), and the instability is not observed to produce any topological change in the plasma sheet configuration.