Dynamics of blobs in scrape-off-layer/shadow regions of tokamaks and linear devices

Linear and nonlinear stability of blob propagation in the tokamak scrape off layer (SOL) and in the SOL/shadows of linear devices are studied. It is found that the most stable blobs, which can propagate as coherent structures for large distance, are the blobs with some specific spatial scale. Larger blobs are subject to the Rayleigh–Taylor (RT) instability, which breaks the blob apart and effectively reduces the scale of new structures. Smaller blobs evolve into mushroom structures typical for nonlinear stages of the RT and Richtmyer–Meshkov instabilities in fluids. Biasing of divertor targets can affect the dynamics of blob propagation. For a large magnitude of biasing potential, a strong deformation and even disintegration of the blob as a coherent structure were observed while the blob passes through the biased region.