Theory and simulation of a high-frequency magnetic drift wave

A theoretical and computational study of a high-frequency electromagnetic drift mode are presented. A fluid theory based upon the resistive magnetohydrodynamic (MHD) equations, which include the Hall term, as well as a kinetic theory based upon the Vlasov equation, are developed. The fluid theory is valid in the regime ω<ω_lh (where ω_lh is the lower hybrid frequency), and yields an approximate dispersion equation ω≂k_yV²_A/L_nΩ_i -iηk²_y, where k_y is the wave number transverse to B₀ and the density gradient, V_A is the Alfvén velocity, L_n is the density gradient scale length, and η is the resistivity. This dispersion equation is valid in the limit L_n≪V_A/Ω_i. Using kinetic theory it is shown that the drift mode transitions to the lower hybrid mode in the limit ω≳ω_lh. The simulation study is based upon the modified MHD equations and the nonlocal nature of the mode is investigated. Applications to sub-Alfvénic plasma expansions, electromagnetic waves in the Earth's magnetosphere, and plasma switches are discussed.