Generation and dynamics of plasma blobs in partially ionized tokamak scrape-off-layer

A theoretical model for the generation and dynamics of plasma blobs in a tokamak scrape-off-layer (SOL) is presented. Specifically, it is suggested that plasma blobs could be generated due to a resistive Rayleigh–Taylor (RRT) instability in partially ionized SOL plasmas that contain equilibrium density and magnetic field inhomogeneities. By using the two-fluid model, a set of nonlinear equations for the low-frequency (in comparison with the ion gyrofrequency) electrostatic modes involved in the RRT instability is derived. In the linear limit, a new dispersion relation is obtained, and analyzed in some limiting cases. The nonlinear equations are useful for studying the dynamics of nonlinearly interacting finite amplitude RRT modes, which are linearly excited due to combined action of ionization as well as of density and magnetic field inhomogeneities in partially ionized SOL plasmas.