Plasma density turbulence in TCV tokamak edge: direct comparison of experiment with 2D simulation

A rather extensive database of plasma density fluctuations in the scrape off layer (SOL) of the TCV tokamak has been compiled using a fast reciprocating Langmuir probe. Data has been obtained for varying plasma current, density, fuel species, field direction and radial position in the SOL of diverted, ohmic discharges including L/H-mode. Analysis of this data has recently shown that the density fluctuations in TCV exhibit statistical properties which are universal across a broad range of discharge conditions. The shape of the probability distribution function (PDF) is uniquely determined everywhere in the SOL by the relative fluctuation level, A=/σ(n). Close to separatrix at low line averaged density, the fluctuations are generally relatively small (A≤10), the PDF is close to Gaussian and correlation times are short. In contrast, in the far SOL, PDF is strongly skewed, correlation times are much longer and the relative fluctuation amplitudes are much higher, characterised by a value of A that saturates to A∼1.7, independently of discharge conditions. This contribution extends the above analysis to a greater range of discharges, now including limiter plasmas, more highly shaped diverted equilibria and some variation in poloidal position of the measurement. In addition and most importantly, direct comparisons have now been made between this TCV experimental data and the results of 2D Edge-SOL Electrostatic (ESEL) fluid turbulence code which include magnetic field curvature and sheath boundary conditions in the SOL region. These simulations produce time series containing large amplitude, radially propagating structures (blobs) which, when analysed statistically in exactly the same way as for the experimental data, are in striking agreement with the measurements, including the observed variation of statistical properties throughout the SOL radial extent. (Author)