Plasma density blobs and drift wave dynamics with shear flow*

Blobs, propagating in tokamak edge toward outer wall, play an important role in the scrape-off layer plasma transport. Although the blobs are studied for about 15 years, the mechanism(-s) of blob formation is still under debates. Recently, the Hasegawa-Mima equation was generalized by considering Boltzmann electrons and keeping all nonlinearities. It follows that the amplitude of wave-packet propagating in the direction of decreasing background plasma density will increase exponentially with the distance travelled until nonlinear effects become important. Nonlinear modification of time averaged plasma density profile results in the formation of large amplitude modes locked in x-direction but still propagating in y-direction, which resembles experimentally observed chain of blobs propagating in poloidal direction. Such specific density profiles, causing the locking of drift waves can form naturally at the edge of tokamak due to neutral ionization source. The impact of the shear flow on the drift wave dynamics is studied to be a factor impeding the development of the large density structure.