Blob sizes and velocities in the Alcator C-Mod scrape-off layer

Abstract

Gas-puff imaging data is used to investigate the dynamics of blob-like structures in the scrape-off layer of Alcator C-Mod. A blob-tracking algorithm is developed and used to compute blob propagation velocities and cross-field sizes for a series of discharges where the line-averaged particle density View the MathML source is varied. We find that the mean radial blob velocity increases from View the MathML source for View the MathML source to View the MathML source for View the MathML source, where is the nG the Greenwald density. The cross-field size of the blobs is independent of the line-averaged particle densities. With increasing View the MathML source the observed blob velocities become larger than predicted by simple blob models for sheath-connected plasma filaments.