Role of edge electric field and poloidal rotation in theL-Htransition

Marked changes in the edge radial electric field ${\mathit{E}}_{\mathit{r}}$ and in the edge poloidal rotation velocity ${\mathit{v}}_{\mathrm{\theta }}$ are important signatures of the L-H transition in the DIII-D tokamak. Shear exists in ${\mathit{E}}_{\mathit{r}}$ and ${\mathit{v}}_{\mathrm{\theta }}$ and increases from the L mode to the H mode. A comparison of experiment with theory shows that shear in ${\mathit{E}}_{\mathit{r}}$ and ${\mathit{v}}_{\mathrm{\theta }}$ is sufficient to suppress edge fluctuations, that ion-orbit loss is large enough to be the source of ${\mathit{v}}_{\mathrm{\theta }}$, and that ${\mathit{E}}_{\mathit{r}}$ and ${\mathit{v}}_{\mathrm{\theta }}$ may play a causal role in the L-H transition.