Generation mechanisms of blobs in tokamak edge plasmas.

Meso-scale structures, driven by curvature and gradB effects, like blobs and ELMs play a very important role in edge and SOL plasma transport in tokamaks. Once these meso-scale structures formed, they exhibit clear convective behavior propagating mainly toward the wall at low B-field side of the torus. The main features of convection mechanisms are relatively well understood. It is widely believed that generation of ELMs is triggered by peeling-ballooning instability. But, the mechanism (-s) and the rate of blob generation are not clear yet. Here we present both analytic and modeling results describing the mechanisms of the blob generation triggered by sub-critical phenomena related to the ballooning drive.