Blob properties in I-mode and ELM-free H-mode compared to L-mode on EAST

Abstract

Abstract The blob properties in I-mode and ELM-free H-mode plasmas compared to L-mode have been investigated on the EAST tokamak, including the blob detection rate N b , size δ b , lifetime τ b and radial velocity v r , b . The blob properties in L-mode and I-mode are similar, and those in ELM-free H-mode are different to them. The blob N b is smaller while τ b is larger in H-mode. The experimental blob size δ b and velocity scalings v r , b − δ b show a good agreement with the theoretical models. The variation in blob properties during the L-I and H-L transitions, and their relations to the scrape-off layer (SOL) density, edge and SOL turbulence, and SOL collisionality are discussed. The suppression of the edge (inside the last closed flux surface) turbulence is not reflected in the blob behavior, while the blob detection rate shows a correlation with the SOL density and its low-frequency (3–50 kHz) fluctuations. In addition, the blob detection rate is found to increase with the divertor collisionality Λ div , indicating a dependence of blob behavior on Λ div . The differences in blob detection rates among the three operating regimes might be due to their different SOL densities and collisionalities. The investigation contributes to understanding the influences of edge and SOL plasma parameters on the blob behavior.