The influence of plasma edge dynamics on blob properties in the stellarator TJ-K

Abstract

Blob properties are studied in the scrape-off layer of the stellarator TJ-K. Langmuir probes and a fast camera are used to investigate the generation rate as well as the blob size and velocity scaling. Discharges with different ion species and magnetic field strengths provide access to a large range of plasma parameters. It was found that almost every large amplitude drift wave in the edge of the confined plasma triggers blob generation in the scrape-off layer, which implies that the birth rate of blobs is determined by the turbulence in the edge. Furthermore, the cross-field size of the blobs seems to correlate with the size of the generating drift waves. Since the observed radial propagation velocity of the blobs is well described by a size dependent blob velocity model, the size coupling between the drift waves and the blobs also has an impact on the blob velocities. Thus, the presented results imply that the dynamics in the edge have a large influence on the blob properties in the scrape-off layer.