Resistive Interchange Instability Research Articles

Neoclassical tearing modes in a tokamak

Linear tearing instability is studied in the banana collisionality regime in tokamak geometry. Neoclassical effects produce significant modifications of Ohm’s law and the vorticity equation, so that the growth rate of tearing modes driven by Δ′ is dramatically reduced compared to the usual resistive magnetohydrodynamic values. Consequences of this result, regarding the presence of pressure-gradient-driven neoclassical resistive interchange instabilities and the evolution of magnetic islands in the Rutherford regime, are discussed.

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

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.

Resistive interchange instability criterion in anisotropic toroidal systems

Ideal (Mercier) and resistive criteria for localized magnetohydrodynamic instabilities are derived for general toroidal systems with anisotropic pressure.

Theory of semicollisional drift-interchange modes in cylindrical plasmas

Resistive interchange instabilities in cylindrical plasmas are studied, including the effects of electron diamagnetic drift, perpendicular resistivity, and plasma compression. The analyses are pertinent to the semicollisional regime where the effective ion gyroradius is larger than the resistive layer width. Both analytical and numerical results show that the modes can be completely stabilized by the perpendicular plasma transport. Ion sound effects, meanwhile, are found to be negligible in the semicollisional regime.

EFFECTS OF RESISTIVE INTERCHANGE INSTABILITIES ON ENERGY CONFINEMENT IN REVERSED-FIELD PINCH

Electron conduction losses due to magnetic flutter produced by resistive interchange instabilities and the resulted confinement deterioration mechanism are investigated analytically. Using approximate solutions of MHD equations for even and odd potential parities, the potential and magnetic perturbation levels at saturation are estimated. These results are used to calculate the stochastic magnetic field diffusion coefficients. An expression for the anomalous electron thermal conductivity is then derived for collision-less and collisional regimes. Scaling laws for energy confinement are infered therefrom.

Numerical solution of the resistive magnetohydrodynamic boundary layer equations

Three different techniques are presented for numerical solution of the equations governing the boundary layer of resistive magnetohydrodynamic tearing and interchange instabilities in toroidal geometry. Good agreement among these methods and with analytical results provides confidence in the correctness of the results. Solutions obtained in regimes where analytical methods fail indicate a new scaling for the tearing mode as well as the existence of a new regime of stability.

Finite Larmor radius theory of resistive instabilities

The hybrid-kinetic model, previously used to investigate stability properties of collisionless high-beta plasmas characterized by finite ion gyroradius, is generalized to include the effects of finite resistivity and gravitation (to simulate toroidal field curvature). Possible applications of the present formalism include investigations of finite ion Larmor radius effects on the stability of screw-pinch and tokamak equilibria against ideal and resistive interchange instabilities as well as tearing modes. A simple example of such an application is carried out for the case of local slow resistive interchange modes within the context of a near-theta-pinch ordering.

Resistive Instabilities of a Viscous Fluid with Horizontal Boundary

The gravitational instabilities of a system consisting of two homogeneous fluids with horizontal interface, in the presence of a uniform horizontal magnetic field, are investigated. The fluids are incompressible and have finite electrical conductivity and viscosity. The dispersion relation, which is obtained for the general case, is then specialized for a lower fluid of vanishing density, viscosity, and conductivity. In the limit of infinite conductivity in the upper fluid, the resulting dispersion relation corresponds to that previously obtained for a conducting fluid supported by a magnetic field against gravity. For finite conductivity in the upper fluid, this procedure avoids the difficulties involved as a result of diffusion across a supporting magnetic field. The effects of viscosity and resistivity on the Rayleigh-Taylor modes are obtained. In addition, a resistive gravitational interchange instability is found, although magnetic shear is absent. It is further established that a small viscosity diminishes the growth rate of the resistive gravitational instability.