Formation of the radial electric field profile in WEST tokamak

Laure Vermare (1) , Guilhem Dif-Pradalier (2, 3) , Pascale Hennequin (1) , James Paul Gunn (2, 3) , Xavier Garbet (3, 2) , Jean-Francois Artaud (3, 2) , Ozgur Gurcan (1) , Clarisse Bourdelle (2, 3) , Frédéric Clairet (2) , Nicolas Fedorczak (2, 3) , Cyrille Honoré (1) , Jorge Morales (2, 3) , Yanick Sarazin (2, 3) , Virginie Grandgirard (2, 3) , Robin Varennes (2, 3) , Didier Vezinet (2, 3) , Mathieu Peret (2, 3) , Rémi Dumont (2, 3) , Marc Goniche (2, 3) , Patrick Maget (2, 3)

1 LPP - Laboratoire de Physique des Plasmas
2 CEA - Commissariat à l'énergie atomique et aux énergies alternatives
3 IRFM - Institut de Recherche sur la Fusion par confinement Magnétique

The shear of the radial electric field at the edge is widely accepted to be responsible for turbulence reduction in edge transport barriers and thought as a key ingredient of the improved confinement of H-mode plasmas. Nevertheless, a full understanding of how its profile builds up at the edge is still lacking. It can either be formulated as the result of a competition between several mechanisms that generate and damp flows or as the result of a non-ambipolar particle flux, which enhances radial charge separation imposing a radial electric field profile. Among possible mechanisms, one can think of turbulence generated flow via Reynolds stress, ion orbit losses, toroidal magnetic ripple and the effect of neutral friction at the edge. Based on previous results obtained on Tore Supra, the radial profile of the perpendicular flow expected in WEST can be separated in three spatial areas. Inside ρ = 0.8, the radial electric field is dominated by losses of thermal ions in the magnetic ripple while between 0.7 < ρ < 0.95, a competition between this latter and the generation of large scale flows by turbulence appears as a possible explanation of the measured poloidal asymmetry of the mean perpendicular velocity. In addition, edge conditions such as contact points and parallel dynamics in the scrape-off-layer (SOL) influence the edge profiles beyond ρ = 0.9 (3). This contribution presents unexpected differences in the radial electric field profile observed in WEST between Lower Single Null (LSN) and Upper Single Null (USN) configurations and a study of the competition between specific mechanisms playing a role in the formation of this profile.

Domaines: Physique [physics]

Laure Vermare, Guilhem Dif-Pradalier, Pascale Hennequin, James Paul Gunn, Xavier Garbet, et al.. Formation of the radial electric field profile in WEST tokamak. FEC 2020 - 28th IAEA fusion energy conference, May 2021, E-Conference, France. . ⟨cea-03520480⟩