Study of resistive drift and resistive interchange modes in a cylindrical plasma with magnetic shear

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Abstract
The resistive drift mode and resistive interchange mode in the presence of magnetic curvature and shear are studied theoretically as well as computationally, based on the electrostatic model equations of isothermal electrons and two‐dimensional cold ions in a cylindrical geometry. There are two branches of unstable modes: one has characteristics similar to the resistive drift wave instability with a real frequency ωr of the order of a diamagnetic frequency ω*, and the other is a curvature driven mode (the resistive interchange instability) with ‖ωr‖=‖ωi‖ localized in the neighborhood of the resonant surface. The growth rates of both of these instabilities are proportional to ν1/2ei in the small νei limit, where νei is the electron–ion collision frequency. The resistive interchange instability is dominant even when the curvature drift frequency is a fraction of ω*. Nonlinear evolution of these instabilities with multihelicity modes based on the model equations demonstrates a global spectrum condensation at the m=0 mode, where m denotes the poloidal mode number. The saturated state generates a region of zonal flows in the azimuthal direction. Since particle transport across the constant φ surface vanishes, the zonal flow is expected to improve global confinement.