Magnetic configuration effects on the Reynolds stress in the plasma edge

Abstract

Breaking the poloidal symmetry of the magnetic shear induced tilt of turbulent structures, by either divertor X-point resistivity or limiter positions, can lead to a finite (residual) contribution to the flux-surface averaged radial-binormal Reynolds stress. This residual stress supports or works against the radial electric field at the plasma edge of a tokamak. The impact of divertor geometry on the poloidal pattern of the Reynolds stress is studied by flux-coordinate-independent fluid simulations. Clear modifications of the Reynolds stress are found due to the magnetic shear in the confined region. The impact of different poloidal limiter positions on the radial electric field and the Reynolds stress is studied by means of magnetic field aligned gyrofluid simulations. Only if the limiter is close to the outer midplane can its position have a substantial effect on the radial electric field.

On the interplay between turbulent forces and neoclassical particle losses in zonal flow dynamics

“…Efforts have been made to understand the causal relation between ZFs, Reynolds stress (RS) and transport [11][12][13]. Based on experimental studies [11,14] and simulations [15], it was found that the RS may exhibit strong poloidal asymmetries, meaning that local RS measurements should be interpreted with great caution, as is the case with the present study. The interplay between turbulent and neoclassical mechanisms was reported for both stellarators [16,17,20] and tokamaks [18].…”

“…Search for the causal relation between Zonal Flows, Reynolds stress (RS) and transport has been re-ported [11,12,13]. In particular, experimental [11,14] and simulation [15] evidence of strong poloidal RS asymmetry points out that care should be taken to prevent a misleading interpretation of local RS measurements, as the ones presented in this study. Furthermore, the interplay between turbulent and neoclassical mechanisms has been identified during transitions in stellarators [16] and tokamaks [17].…”

Formation of the radial electric field profile in the WEST tokamak

“…This competition introduces an explicit dependence on the safety factor. In particular, considering the turbulent drive, the breaking of the poloidal symmetry of the magnetic shear with X-point or contact point with a limiter, can induce significant contribution on the E r profile [Fed+13;Man+18]. In this spirit, investigation on edge turbulence generating flows via both magnetic and velocity shear, based on a reduced model [Per+21] are in progress.…”

Geodesic acoustic modes in magnetic confinement devices

“…As a final point, configuration effects, such as magnetic shear ŝ, on the RS were discussed in [497] where simulations showed a strong polidal asymmetry in the RS. The role of the X-point in breaking poloidal symmetry of ŝ was noted-circular plasmas have up-down asymmetric RS, while divertor configuration is more complex with high RS in a narrow radial strip localized to the X-point.…”