Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak
Abstract
The I-mode regime, routinely observed on the Alcator C-Mod tokamak, is characterized by an edge energy transport barrier without an accompanying particle barrier and with broadband instabilities, known as weakly coherent modes (WCM), believed to regulate particle transport at the edge. Recent experiments on the DIII-D tokamak exhibit I-mode characteristics in various physical quantities. These DIII-D plasmas evolve over long periods, lasting several energy confinement times, during which the edge electron temperature slowly evolves towards an H-mode-like profile, while maintaining a typical L-mode edge density profile. During these periods, referred to as I-mode phases, the radial electric field at the edge also gradually reaches values typically observed in H-mode. Density fluctuations measured with the phase contrast imaging diagnostic during I-mode phases exhibit three features typically observed in H-mode on DIII-D, although they develop progressively with time and without a sharp transition: the intensity of the fluctuations is reduced; the frequency spectrum is broadened and becomes non-monotonic; two dimensional space-time spectra appear to approach those in H-mode, showing phase velocities of density fluctuations at the edge increasing to about 10 km s-1. However, in DIII-D there is no clear evidence of the WCM. Preliminary linear gyro-kinetic simulations are performed in themore »
- Authors:
-
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- General Atomics, San Diego, CA (United States)
- Univ. of California, Los Angeles, CA (United States)
- Publication Date:
- Research Org.:
- Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE Advanced Research Projects Agency - Energy (ARPA-E)
- OSTI Identifier:
- 1557846
- Alternate Identifier(s):
- OSTI ID: 1238853
- Grant/Contract Number:
- FG02-94ER54235; FC02-0454698; FG02-08ER54984
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Nuclear Fusion
- Additional Journal Information:
- Journal Volume: 55; Journal Issue: 9; Journal ID: ISSN 0029-5515
- Publisher:
- IOP Science
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 70 PLASMA PHYSICS AND FUSION TECHNOLOGY
Citation Formats
Marinoni, A., Rost, J. C., Porkolab, M., Hubbard, A. E., Osborne, T. H., White, A. E., Whyte, D. G., Rhodes, T. L., Davis, E. M., Ernst, D. R., and Burrell, K. H. Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak. United States: N. p., 2015.
Web. doi:10.1088/0029-5515/55/9/093019.
Marinoni, A., Rost, J. C., Porkolab, M., Hubbard, A. E., Osborne, T. H., White, A. E., Whyte, D. G., Rhodes, T. L., Davis, E. M., Ernst, D. R., & Burrell, K. H. Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak. United States. https://doi.org/10.1088/0029-5515/55/9/093019
Marinoni, A., Rost, J. C., Porkolab, M., Hubbard, A. E., Osborne, T. H., White, A. E., Whyte, D. G., Rhodes, T. L., Davis, E. M., Ernst, D. R., and Burrell, K. H. Mon .
"Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak". United States. https://doi.org/10.1088/0029-5515/55/9/093019. https://www.osti.gov/servlets/purl/1557846.
@article{osti_1557846,
title = {Characterization of density fluctuations during the search for an I-mode regime on the DIII-D tokamak},
author = {Marinoni, A. and Rost, J. C. and Porkolab, M. and Hubbard, A. E. and Osborne, T. H. and White, A. E. and Whyte, D. G. and Rhodes, T. L. and Davis, E. M. and Ernst, D. R. and Burrell, K. H.},
abstractNote = {The I-mode regime, routinely observed on the Alcator C-Mod tokamak, is characterized by an edge energy transport barrier without an accompanying particle barrier and with broadband instabilities, known as weakly coherent modes (WCM), believed to regulate particle transport at the edge. Recent experiments on the DIII-D tokamak exhibit I-mode characteristics in various physical quantities. These DIII-D plasmas evolve over long periods, lasting several energy confinement times, during which the edge electron temperature slowly evolves towards an H-mode-like profile, while maintaining a typical L-mode edge density profile. During these periods, referred to as I-mode phases, the radial electric field at the edge also gradually reaches values typically observed in H-mode. Density fluctuations measured with the phase contrast imaging diagnostic during I-mode phases exhibit three features typically observed in H-mode on DIII-D, although they develop progressively with time and without a sharp transition: the intensity of the fluctuations is reduced; the frequency spectrum is broadened and becomes non-monotonic; two dimensional space-time spectra appear to approach those in H-mode, showing phase velocities of density fluctuations at the edge increasing to about 10 km s-1. However, in DIII-D there is no clear evidence of the WCM. Preliminary linear gyro-kinetic simulations are performed in the pedestal region with the GS2 code and its recently upgraded model collision operator that conserves particles, energy and momentum. The increased bootstrap current and flow shear generated by the temperature pedestal are shown to decrease growth rates, thus possibly generating a feedback mechanism that progressively stabilizes fluctuations.},
doi = {10.1088/0029-5515/55/9/093019},
journal = {Nuclear Fusion},
number = 9,
volume = 55,
place = {United States},
year = {Mon Aug 17 00:00:00 EDT 2015},
month = {Mon Aug 17 00:00:00 EDT 2015}
}
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