Role of edge electric field and poloidal rotation in the<i>L</i>-<i>H</i>transition

Abstract

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