Analysis of L-mode turbulence in the MAST boundary plasma

Turbulent transport in the edge of Ohmic and neutral beam heated L-mode plasmas on MAST has been diagnosed using Langmuir probes, an edge Thomson scattering system and a fast, 2D visible light camera and modelled using the BOUT two-fluid Braginskii code. Results suggest that electostatic drift wave turbulence (ESDWT), 1 or 2 cm inside the separatrix and correlated for long timescales (several 100 ms), generates density (and temperature) fluctuations in the plasma through turbulent mixing of eddies close to the separatrix. These fluctuations are then propelled into and across the scrape-off layer, primarily by curvature drive (i.e. interchange-like), where they appear as elongated plasma filaments with short timescale correlation (dispersing in ∼ 30-60 μs). Close to the region of ESDWT, the turbulent fluctuations are symmetrically distributed around a mean and corr elated for long timescales. Farther out in the SOL, the fluctuations are dominated by plasma filaments, which have a positively skewed distribution and short timescale correlations. (author)