Lower-hybrid-drift instability in field reversed plasmas

The nonlocal structure of the lower-hybrid-drift instability is investigated in a reversed field configuration. The calculation includes electromagnetic effects and ∇B electron orbit modifications, which must be considered in the high β region of the current sheet. The eigenmodes are trapped in a potential well centered symmetrically on either side of the neutral layer at ‖x‖∼λ (λ is the scale length of the current sheet). The fundamental mode is well localized away from the neutral line with a half-width Δx∼ (λ/ky)1/2<<λ, where ky∼Ωe(Ti/me)1/2 for the fastest growing mode. Higher order modes, however, have growth rates comparable to the fundamental mode and are much more global. In the cold electron limit (Te=0), the higher order modes with ∂/∂x∼ky can propagate throughout the entire sheet. In the warm electron limit (Te≠0), the electron ∇B drift-wave resonance damps the mode and prevents the penetration of the mode closer than ‖x‖p∼λ (Te/2Ti) 1/2 of the neutral line. The effects of this instability on magnetic energy dissipation and its role in the Los Alamos field reversed theta pinch are discussed.