TH/P4-43 · Influence Of Anomalous Transport Phenomena On Onset Of Neoclassical Tearing Modes In Tokamaks
S.V. Konovalov1), A.B. Mikhailovskii1), T. Ozeki2), T. Takizuka2), M. S. Shirokov1), N. Hayashi2)
1) Institute of Nuclear Fusion, RRC "Kurchatov Institute", Moscow, Russian Federation
2) Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka-machi, Naka-gun, Ibaraki-ken, Japan
Abstract: Influence of anomalous perpendicular heat transport and anomalous ion perpendicular viscosity on conditions of Neoclassical Tearing Mode (NTM) onset is studied theoretically. Importance of the two-fluid description of the perturbed plasma for evolution of the neoclassical islands is demonstrated. Series of different parallel transport mechanisms competitive to anomalous cross-island heat transport in formation of the perturbed electron and ion temperature profiles within the island are considered. The perturbed electron temperature profile is established in competition between anomalous perpendicular electron heat conductivity and parallel electron heat convection or heat conductivity. While in formation of the ion perturbed temperature profile perpendicular ion heat conductivity is balanced by the parallel transports associated with ion inertia for an island rotating with subsonic frequency or with island rotation with respect to plasma for supersonic islands. Analytical solutions to all four above heat balance equations were found and perturbed electron and ion temperatures profiles were calculated rigorously. The partial contributions from the plasma electron and ion temperature perturbations in the bootstrap drive of the mode and magnetic curvature effect were then accounted in construction of a generalized transport threshold model of NTMs. Our calculations demonstrate that taking into account the curvature effect weakening in the generalized transport threshold model predicts notable improvement of NTM stability. The anomalous perpendicular ion viscosity was shown to modify collisionality dependence of polarization current effect reducing it to the low collisionality limit. In its turn the bootstrap drive of NTM in the presence of this viscosity was found to be dependent on the island rotation frequency and direction. For island rotating in direction of the electron diamagnetic drift viscosity effect was shown to be stabilizing. The role of viscosity effect grows rapidly with rise of the plasma ion temperature. We found that generalized transport threshold model, which describes weakening the bootstrap drive with allowance for viscous corrections and weakening the curvature effect at small island width, looks more relevant to interpretation of the experimental data than the model based on the stabilizing polarization current effect.
Keywords: anomalous transport, neoclassical tearing modes,