Overview of edge electrostatic turbulence experiments on TCV
Experiments on edge turbulence in the TCV tokamak have been performed for the first time at the beginning of 2003. This paper presents an overview of some of the results obtained, concentrating in particular on two areas: universality of density fluctuations and the dynamical coupling between radial turbulent-driven fluxes and parallel flows. Plasma fluctuations in the edge of the TCV tokamak have been found to exhibit statistical properties which are universal across a broad range of discharge conditions. Analysis of the time series of density fluctuations in the entire scrape-off layer (SOL) region from just inside the magnetic separatrix to the plasma-wall interface, yields a probability distribution function (PDF) of density which conforms closely to a Gamma distribution. In the wall vicinity, the density fluctuations exhibit clear evidence of self-similarity and are characterised by a PDF with universal shape and with a standard deviation proportional to the mean density. It is also found that radial particle-flux fluctuations scale solely with the mean density. Such findings indicate that it may be possible to improve the prediction of transport in the critical plasma-wall interaction region of future large-scale tokamaks. Recent experiments on JET [C. Hidalgo et al.: Phys. Rev. Lett. 91 (2003) 065001] have investigated a possible link between turbulent transport and the parallel flows. Similar experiments have been performed on TCV for a variety of plasma conditions and flow magnitudes. Although correlations have been found as seen on JET, especially in the wall vicinity, it appears that the magnitude of the coupling is insufficient to drive any significant flow.