Study of near SOL decay lengths in AUG under attached and detached divertor conditions

By comparing upstream temperature decay width, , with the scaling of the SOL power decay width, _∥, based on the downstream IR measurements, it is found that a simple relation based on classical electron conduction can relate and _∥ well. The combined dataset can be described by both a single scaling and a separate scaling for H- and L-mode. For the single scaling, a strong inverse dependence of, on the separatrix temperature, , is found, suggesting the classical parallel Spitzer-Harm conductivity as dominant mechanism controlling the SOL width in both L-mode and H-mode over a large set of plasma parameters. This dependence on explains why, for the same global plasma parameters, _∥ in L-mode is approximately twice that in H-mode. The single scaling for both H- and L-mode, implies a common form of perpendicular heat transport coefficient, ∝^// ( for both H- and L-mode plasma). However, the possibility of the separate scalings for different regimes also exits, which gives results similar to those previously reported for the H-mode, but here the wider SOL width for L-mode plasmas is explained simply by the larger premultiplying coefficient. Using different coefficients for H- and L-mode plasmas, gives ∝ ^// ( for H-mode plasma and for L-mode plasma). Based on the dataset of this paper, there is no significant evidence for any of the two models. Further experiments are required to give a definitive answer.