Intermittent convection in the boundary of DIII-D

Abstract

Intermittent plasma objects (IPOs) featuring higher pressure than the surrounding plasma, and responsible for ∼50% of the E× B T radial transport, are observed in the scrape-off layer (SOL) and edge of the DIII-D tokamak. The skewness (i.e., asymmetry of fluctuations from the average) of probe and BES intermittent data suggest IPO formation at or near the last closed flux surface (LCFS) and the existence of hole–IPO pairs. The particle content of the IPOs at the LCFS is linearly dependent on the discharge density, however, when normalized to the local averaged density, it is fairly insensitive to density variations. It is also shown that the IPOs thermalize with the background plasma within 1 cm of the LCFS. The IPOs appear in the SOL of both L and H mode discharges carrying ∼50% of the total SOL radial E× B T transport at all radii. However, the total flux and the IPO contribution, are highly reduced in H-mode conditions due to the increased confinement.