Edge radial electric field studies via charge exchange recombination spectroscopy on the Alcator C-Mod Tokamak

[摘要] (cont.) peak (3-4mm) just inside of the LCFS. In Ohmic L-mode plasmas Er is positive near the last closed flux surface (LCFS) and becomes more negative with distance into the plasma. In H-mode plasmas E, is positive in the core, but forms a deep negative well, relative to its L-mode values, just inside of the LCFS. These results are qualitatively consistent with the observations made on other machines. However, the C-Mod H-mode Er wells are unprecedeited in depth (up to 300kV/m) and the narrow E, well widths (5mm), as compareJ to results from other tokamaks, suggest a scaling with machine size. The measured Er well widths have been compared to theoretical scalings for the edge pedestal and no significant correlation was observed with any of the predictions. In fact, very little variation of the E, well width is observed in general. Howc:ver, the depth of the E, well, or alternatively the magnitude of the E, shear (constant width), shows a strong correlation with improved plasma energy confinement. It also correlates well with the edge electron temperature and pressure pedestal heights (and gradients). It is not, however, very sensitive to variation in the edge electron density pedestal height. These results are an indication that the energy and particle transport have different relationships to Er, with energy transport more directly linked. The radial electric field results from ELM-free H-mode and I-mode plasmas support this interpretation.

[发布机构] Massachusetts Institute of Technology