Dynamics of turbulent transport in the scrape-off layer of the CASTOR tokamak

In this paper, the propagation of turbulent events along radial and poloidal probe arrays in the scrape-off layer (SOL) of the tokamak CASTOR [ M. Hron et al., Czech. J. Phys. 49, 181 (1999) ] is observed using a novel correlation technique. The typical turbulent structures appear as dipoles on the floating potential signals and as positive bursts on the density. It is found that both dipoles and density bursts propagate over long radial distances in the SOL while propagating poloidally. A comparison of the measured velocities of the potential and density fluctuations shows that the density structures move radially faster than the potential ones. This allows us to understand how the density is convected by the turbulence. The density moves radially along the potential valleys created by the poloidal dipoles without modifying them. In the framework of an interchange turbulence, this property indicates that charge exchange collisions with neutrals in the SOL of CASTOR lead to a high viscosity that damps the zonal flows.