Transport by intermittent convection in the boundary of the DIII-D tokamak

Intermittent plasma objects (IPOs) featuring higher pressure than the surrounding plasma, and responsible for similar to 50% of the ExB(T) radial transport, are observed in the scrape off layer (SOL) and edge of the DIII-D tokamak [J. Watkins , Rev. Sci. Instrum. 63, 4728 (1992)]. Conditional averaging reveals that the IPOs, produced at a rate of similar to 3x10(3) s(-1), are positively charged and also polarized, featuring poloidal electric fields of up to 4000 V/m. The IPOs move poloidally at speeds of up to 5000 m/s and radially with ExB(T)/B-2 velocities of similar to 2600 m/s near the last closed flux surface (LCFS), and similar to 330 m/s near the wall. The IPOs slow down as they shrink in radial size from 4 cm at the LCFS to 0.5 cm near the wall. The IPOs appear in the SOL of both L and H mode discharges and are responsible for nearly 50% of the SOL radial ExB transport at all radii; however, they are highly reduced in absolute amplitude in H-mode conditions. (C) 2001 American Institute of Physics.