Abstract
High-resolution charge-exchange recombination spectroscopic measurements of B ions have enabled the first spatially resolved calculations of the radial electric field (E) in the Alcator C-Mod pedestal region [E. S. Marmar, Fusion Sci. Technol. 51, 261 (2006)]. These observations offer new challenges for theory and simulation and provide for important comparisons with other devices. Qualitatively, the field structure observed on C-Mod is similar to that on other tokamaks. However, the narrow high-confinement mode (H -mode) E well widths (5 mm) observed on C-Mod suggest a scaling with machine size, while the observed depths (up to 300 kV/m) are unprecedented. Due to the strong ion-electron thermal coupling in the C-Mod pedestal, it is possible to infer information about the main ion population in this region. The results indicate that in H -mode the main ion pressure gradient is the dominant contributor to the Er well and that the main ions have significant edge flow. C-Mod H -mode data show a clear correlation between deeper E wells, higher confinement plasmas, and higher electron temperature pedestal heights. However, improved L -mode (I -mode) plasmas exhibit energy confinement equivalent to that observed in similar H -mode discharges, but with significantly shallower E wells. I -mode plasmas are characterized by H -mode-like energy barriers, but with L -mode-like particle barriers. The decoupling of energy and particle barrier formation makes the I -mode an interesting regime for fusion research and provides for a low collisionality pedestal without edge localized modes.
Original language | English |
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Article number | 056103 |
Number of pages | 12 |
Journal | Physics of Plasmas |
Volume | 16 |
Issue number | 5 |
Early online date | 12 Mar 2009 |
DOIs | |
Publication status | Published - 2009 |