Edge radial electric field structure and its connections to H-mode confinement in Alcator C-Mod Plasmas
High-resolution charge-exchange recombination spectroscopic measurements of B[superscript 5+] ions have enabled the first spatially resolved calculations of the radial electric field (E[subscript r]) in the Alcator C-Mod pedestal region [ E. S. Marmar, Fusion Sci. Technol. 51, 261 (2006) ]. These ob...
| Main Authors: | , , , , , , , , , , , , , |
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| Other Authors: | |
| Format: | Article |
| Language: | en_US |
| Published: |
American Institute of Physics
2010
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| Online Access: | http://hdl.handle.net/1721.1/55957 https://orcid.org/0000-0001-8319-5971 https://orcid.org/0000-0002-9001-5606 https://orcid.org/0000-0002-7841-9261 https://orcid.org/0000-0002-4438-729X https://orcid.org/0000-0002-0349-1736 |
| Summary: | High-resolution charge-exchange recombination spectroscopic measurements of B[superscript 5+] ions have enabled the first spatially resolved calculations of the radial electric field (E[subscript r]) 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[subscript r] 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[subscript r] 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[subscript r] 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. |
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