Comparison of plasma turbulence in the low- and high-field Scrape-Off Layers in the T-10 tokamak

Experimental investigation of the Scrape-Off Layer (SOL) turbulence and the perpendicular anomalous particle transport in the high density regime in the T-10 tokamak is presented. Comparison of the plasma parameters measured at the low-field side (LFS) and the high-field side (HFS) of the tokamak shows that the inboard turbulence essentially differs from the outboard one. Turbulence has an intermittent character but the fluctuation level of the inboard ion saturation current is about two times lower than at the LFS. The radial turbulent particle flux and the effective perpendicular diffusion coefficient measured at the LFS are about 3–5 times higher than those observed at the HFS. Enhanced perpendicular particle flux at the LFS is defined by the high density plasma structures formed in the vicinity of the last closed flux surface. The poloidal electric field inside the high density structures has different directions at the inboard and outboard sides of the plasma column. The radial electric drift induced by the poloidal electric field is directed towards the vacuum vessel at both the LFS and the HFS. These experiments support the hypothesis that SOL parallel flow might be caused by an additional mechanism such as 'ballooning' transport, which generates a larger flux of particles from the core into the SOL at the outer mid-plane.