Mach probe measurements of peripheral plasma rotation evolution during L–H transition and ITB decay in the TUMAN-3M tokamak

Abstract

Radial electric field and associated sheared plasma rotation is known to play crucial role in the turbulent transport suppression and improved confinement development. Toroidal and poloidal rotation velocity evolutions at the plasma edge were studied on the TUMAN-3M tokamak using four-tip movable Mach probe. Measurements were performed in two modes of plasma confinement: H-mode transition (featured by peripheral transport barrier formation), and transient internal transport barrier (ITB) formation; both in ohmic heating scenario. The measurements were performed in the vicinity of a last closed flux surface, both in scrape-off layer and core plasmas. In ohmic H-mode, virtually no perturbation of toroidal rotation velocity was observed, whereas poloidal rotation velocity profile underwent gradual evolution after the transition. Surprisingly, poloidal rotation changed not in tact with radial electric field, but followed density gradient built up at the edge transport barrier region. In transient ITB scenario, a noticeable perturbation of toroidal rotation velocity was observed just after the ITB decay, indicating, probably, the outflux of the toroidal momentum due to confinement degradation. The Mach probe data obtained in both the scenarios are compared to available data on plasma density and temperature profiles, radial electric field and rotation velocity of impurity ions.