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Title: H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod

Authors:
 [1];  [1];  [2];  [3];  [4];  [1];  [4];  [4];  [4];  [4];  [4];  [4];  [1];  [4]
  1. Massachusetts Institute of Technology (MIT)
  2. University of Texas, Fusion Research Center, Austin
  3. ORNL
  4. Plasma Sciences and Fusion Center, Massachusetts Institute of Technology (MIT)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1118762
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: 48th Annual Meeting of the Division of Plasma Physis of the American Physical Society (APS), Philadelphia, PA, USA, 20061030, 20061103
Country of Publication:
United States
Language:
English

Citation Formats

Hubbard, A. E., Hughes, J., Bespamyatnov, I. O., Biewer, Theodore M, Cziegler, I., LaBombard, Brian, McDermott, R., Rice, J. E., Rowan, W. L., Snipes, J. A., Terry, J. L., Wolfe, S. M., Wukitch, Dr. Steve, and Alcator C-Mod Group,. H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod. United States: N. p., 2007. Web.
Hubbard, A. E., Hughes, J., Bespamyatnov, I. O., Biewer, Theodore M, Cziegler, I., LaBombard, Brian, McDermott, R., Rice, J. E., Rowan, W. L., Snipes, J. A., Terry, J. L., Wolfe, S. M., Wukitch, Dr. Steve, & Alcator C-Mod Group,. H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod. United States.
Hubbard, A. E., Hughes, J., Bespamyatnov, I. O., Biewer, Theodore M, Cziegler, I., LaBombard, Brian, McDermott, R., Rice, J. E., Rowan, W. L., Snipes, J. A., Terry, J. L., Wolfe, S. M., Wukitch, Dr. Steve, and Alcator C-Mod Group,. Mon . "H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod". United States. doi:.
@article{osti_1118762,
title = {H-mode pedestal and threshold studies over an expanded operating space on Alcator C-Mod},
author = {Hubbard, A. E. and Hughes, J. and Bespamyatnov, I. O. and Biewer, Theodore M and Cziegler, I. and LaBombard, Brian and McDermott, R. and Rice, J. E. and Rowan, W. L. and Snipes, J. A. and Terry, J. L. and Wolfe, S. M. and Wukitch, Dr. Steve and Alcator C-Mod Group,},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • This paper reports on studies of the edge transport barrier and transition threshold of the high confinement (H) mode of operation on the Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)], over a wide range of toroidal field (2.6-7.86 T) and plasma current (0.4-1.7 MA). The H-mode power threshold and edge temperature at the transition increase with field. Barrier widths, pressure limits, and confinement are nearly independent of field at constant current, but the operational space at high B shifts toward higher temperature and lower density and collisionality. Experiments with reversed field and current showmore » that scrape-off-layer flows in the high-field side depend primarily on configuration. In configurations with the Bx{nabla}B drift away from the active X-point, these flows lead to more countercurrent core rotation, which apparently contributes to higher H-mode thresholds. In the unfavorable case, edge temperature thresholds are higher, and slow evolution of profiles indicates a reduction in thermal transport prior to the transition in particle confinement. Pedestal temperatures in this case are also higher than in the favorable configuration. Both high-field and reversed-field results suggest that parameters at the L-H transition are influencing the evolution and parameters of the H-mode pedestal.« less
  • Recent advances in gyrokinetic simulation of core turbulence and associated transport requires an intensified experimental effort to validate these codes using state of the art synthetic diagnostics to compare simulations with experimental data. A phase contrast imaging (PCI) diagnostic [M. Porkolab, J. C. Rost, N. Basse et al., IEEE Trans. Plasma Sci. 34, 229 (2006)] is used to study H-mode plasmas in Alcator C-Mod [M. Greenwald, D. Andelin, N. Basse et al., Nucl. Fusion 45, S109 (2005)]. The PCI system is capable of measuring density fluctuations with high temporal (2 kHz-5 MHz) and wavenumber (0.5-55 cm{sup -1}) resolution. Recent upgradesmore » have enabled PCI to localize the short wavelength turbulence in the electron temperature gradient range and resolve the direction of propagation (i.e., electron versus ion diamagnetic direction) of the longer wavelength turbulence in the ion temperature gradient (ITG) and trapped electron mode range. The studies focus on plasmas before and during internal transport barrier formation in an enhanced D{sub {alpha}} H-mode plasma assisted with ion cyclotron resonance frequency heating. Nonlinear GYRO simulations have also been performed [J. Candy and R. E. Waltz, Phys. Rev. Lett. 91, 045001 (2003)] and the predicted fluctuation is compared against experimental measurements through a synthetic PCI diagnostic method. The simulated fluctuations from GYRO agree with experimental measurements in the ITG regime. GYRO also shows good agreement in transport predictions with experimental measurements after reducing the ion temperature gradient ({approx}15%) and adding ExB shear suppression, all within the experimental uncertainty.« less
  • Measurements of the steep transport barrier at the edge of the Alcator C-Mod tokamak [I. H. Hutchinson {ital et al.}, Phys. Plasmas {bold 1}, 1511 (1994)] are presented. The parameters at the top of this barrier are in the range T{sub e}=150{endash}750 eV and n{sub e}=0.5{minus}3.3{times}10{sup 20} m{sup {minus}3}, depending on the confinement regime. Type III edge localized modes (ELMs) have an upper temperature limit. T{sub e} pedestal profiles show a barrier width {Delta}{sub T}{approx_equal}8 mm. Soft x-ray emissivity profiles are narrower, with {Delta}=2{endash}4 mm. Edge currents are calculated to alter the ideal stability boundary favorably, leading to ideally stablemore » pedestal profiles. High frequency, broadband, edge density fluctuations are sometimes observed in H-mode (high-confinement mode) and are associated with enhanced particle transport. Coherent magnetic fluctuations localized near the pedestal are also seen. {copyright} {ital 1998 American Institute of Physics.}« less