Turbulent transport studies in JET edge plasmas in X-point configurations

Reciprocating Langmuir probe measurements were obtained in dedicated JET experiments to investigate turbulent transport at the edge and SOL plasmas. The measured turbulent radial particle flux, radial velocity and diffusion coefficient were compared with results from the 2-D plasma edge code B2-EIRENE, Qualitatively, the experimental results and the modelling calculations show a similar behaviour, with the radial particle Aux increasing from inside the separatrix to some point in the SOL and then decreasing again. However, there is a quantitative disagreement between code calculations and measurements in X-point plasmas. Two explanations have been proposed to reconcile these observations: first temperature fluctuations, with the appropriate phase could modify the derived particle turbulent flux. Second, code simulations including the effect of drifts at the plasma edge show that large convective cells appear in this region, leading to large parallel flows in the SOL, which have been measured. Such drifts could lead to a net inwards particle pinch which could compensate for the measured large turbulent out flux. (C) 2001 Elsevier Science B.V. All rights reserved.