Spatiotemporal variations of blob properties in ASDEX Upgrade

Prior experiments in ASDEX Upgrade documented a change in the characteristic blob properties in high-density discharges around L = 1. This is in agreement with analytical blob models predicting a change in the relevant blob regime around this threshold value in the effective collisionality. If this explanation is correct, this would imply that a) different blob regimes would co-exist in the SOL of ASDEX Upgrade and b) blobs generated in high- L regions would "reattach" to the walls while they propagate radially outwards. The presented experiments show that these effects are indeed observed in ASDEX Upgrade. While these results represent further evidence that the present blob theory is able to describe several features of turbulent structures in the SOL of fusion experiments, they are also of practical importance for the heat and particle deposition on the walls. The latter is the case since a change in the blob dynamics by reattachment determines if and where the blobs will end up in the divertor region or will reach the first wall. Furthermore these experiments show that it would in principle be possible to influence the blob dynamics by varying L in the SOL (e. g. by the parallel connection length).