Nonlinear effect on the plasma blob propagation in the scrape-off layer

The 2D Hasegawa-Wakatani-type model equation is introduced to investigate the blob propagation in the scrape-off layer. The effect of the density nonlinearity on the blob propagation is investigated, focusing on the blob size effect. It is found that in the regime with the large blob size where the interchange instability is dominant, the theoretical estimation of the blob propagation velocity agrees well with the simulation results. However, in the regime with small blob size where the Kelvin-Helmholtz instability is dominant, it does not work well. This is because the blob breaks up into pieces in this regime. The center-of-mass velocity is estimated in this regime to understand the characteristic of the blob propagation.