Kinetic theory of electrostatic “bounce” modes in two-dimensional current sheets

The role of trapped particles in the destabilization of two-dimensional (2D) current sheets is investigated for applications to theories of magnetospheric substorms. Considering a 2D “Lembège and Pellat” equilibrium, the linearized gyrokinetic Vlasov–Maxwell equations are solved for electrostatic perturbations with periods close to the typical electron bounce period (τbe). The particle bounce motion is approximated to its first Fourier component (ωb=2π/τb) which allows the explicit time integration of Vlasov equation and the calculation of the nonlocal particle response. The dispersion equation of the electrostatic bounce modes is derived from the quasineutrality condition. It is shown that the bounce modes exist in a narrow domain of electron-to-ion temperature ratio (Te/Ti varying from 0.2 to 1.4), with large growth rates (δ∼0.2ω), leading to current sheet destabilization over time scales of 1–2 min.