Anomalous Perpendicular Viscosity Research Articles

Asymmetry of parallel flow on the Large Helical Device

An asymmetric parallel return flow, which modifies the parallel component of the flow, is expected to meet the zero divergence of the flow on a flux surface based on the common neoclassical theory for torus plasma. The full flow structure is measured by charge exchange spectroscopy on the Large Helical Device. Inboard/outboard asymmetry of the parallel flow is observed according to the full flow profile measurement. Flow asymmetry is considered to be induced by the Pfirsch–Schlüter flow closely associated with the radial electric field. A linear relationship between the integrated flow asymmetry and the electric potential difference is obtained in different magnetic fields and configurations. A model based upon the incompressibility of the flow is applied to acquire a geometric factor hB, which only connects to the magnetic configuration from the experiment. The asymmetric component of the parallel flow measured is compared with the asymmetric component of parallel flow calculated in the incompressibility conditions of flow on the magnetic flux surface. The measured asymmetric flow is consistent with the calculation in plasma with a small toroidal torque input in the inward shifted configuration. However, the measured asymmetric flow is significantly smaller than that calculated for plasma with a large toroidal torque or in the outward shifted configuration. One possible explanation for this variation could be radial transport due to anomalous perpendicular viscosity as well as strongly poloidally asymmetric radial flow.

Transport threshold model of neoclassical tearing modes in the presence of anomalous perpendicular viscosity

Bootstrap drive of neoclassical tearing modes (NTMs) in the presence of anomalous perpendicular viscosity is calculated. Viscosity is shown to lead to dependence of the perturbed bootstrap current on the perturbed electric field. As a result, the bootstrap drive is qualitatively modified by the island rotation frequency and direction of the island rotation. The modified bootstrap drive is incorporated into the transport threshold model of NTMs.

Ion-temperature-gradient-driven instability and anomalous ion heating in reversed-field pinches

A possible mechanism is suggested for direct ion heating in reversed-field pinches (RFP). The ion temperature gradient mode induces collisionless ion perpendicular viscosity which damps the velocity fluctuations associated with resistive magnetohydrodynamic (MHD) mode activity. It is found that the growth rate of the ηi instability is much larger than that in a tokamak, because the effects of both bad magnetic curvature and negative compressibility are enhanced in a RFP configuration. The anomalous perpendicular viscosity coefficient is estimated from the mixing length argument and the corresponding ion heating power due to viscous dissipation is found sufficient to balance the ion conductive losses.

Effect of turbulent diffusion on collisionless tearing instabilities

The direct interaction approximation is used to obtain the kinetic electron response in the presence of drift-wave turbulence. Primary effects on the tearing mode equations are a diffusive broadening of the conductivity and an anomalous perpendicular viscosity. The first has a negligible effect on collisionless current channel modes. The viscous term, however, produces significant stabilization of the m = 1 mode for levels of turbulence much smaller than those expected.