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Progress in understanding the enhanced pedestal H-mode in NSTX

Publication ,  Journal Article
Gerhardt, SP; Canik, JM; Maingi, R; Battaglia, D; Bell, RE; Guttenfelder, W; Leblanc, BP; Smith, DR; Yuh, H; Sabbagh, S
Published in: Nuclear Fusion
August 1, 2014

This paper describes the enhanced pedestal (EP) H-mode observed in the National Spherical Torus Experiment (NSTX). The defining characteristics of EP H-mode are given, namely (i) transition after the L- to H-mode transition, (ii) region of very steep ion temperature gradient, and (iii) associated region of strong rotational shear. A newly observed long-pulse EP H-mode example shows quiescent behaviour for as long as the heating and current drive sources are maintained. Cases are shown where the region of steep ion temperature gradient is located at the very edge, and cases where it is shifted up to 10cm inward from the plasma edge; these cases are united by a common dependence of the ion temperature gradient on the toroidal rotation frequency shear. EP H-mode examples have been observed across a wide range of q95 and pedestal collisionality. No strong changes in the fluctuation amplitudes have been observed following the EP H-mode transition, and transport analysis indicates that the ion thermal transport is comparable to or less than anticipated from a simple neoclassical transport model. Cases are shown where EP H-modes were reliably generated, though these low-q95 examples were difficult to sustain. A case where an externally triggered edge localized mode (ELM) precipitates the transition to EP H-mode is also shown, though an initial experiment designed to trigger EP H-modes in this fashion was unsuccessful. © 2014 IAEA, Vienna.

Duke Scholars

Published In

Nuclear Fusion

DOI

EISSN

1741-4326

ISSN

0029-5515

Publication Date

August 1, 2014

Volume

54

Issue

8

Related Subject Headings

  • Fluids & Plasmas
  • 5106 Nuclear and plasma physics
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics
 

Citation

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Gerhardt, S. P., Canik, J. M., Maingi, R., Battaglia, D., Bell, R. E., Guttenfelder, W., … Sabbagh, S. (2014). Progress in understanding the enhanced pedestal H-mode in NSTX. Nuclear Fusion, 54(8). https://doi.org/10.1088/0029-5515/54/8/083021
Gerhardt, S. P., J. M. Canik, R. Maingi, D. Battaglia, R. E. Bell, W. Guttenfelder, B. P. Leblanc, D. R. Smith, H. Yuh, and S. Sabbagh. “Progress in understanding the enhanced pedestal H-mode in NSTX.” Nuclear Fusion 54, no. 8 (August 1, 2014). https://doi.org/10.1088/0029-5515/54/8/083021.
Gerhardt SP, Canik JM, Maingi R, Battaglia D, Bell RE, Guttenfelder W, et al. Progress in understanding the enhanced pedestal H-mode in NSTX. Nuclear Fusion. 2014 Aug 1;54(8).
Gerhardt, S. P., et al. “Progress in understanding the enhanced pedestal H-mode in NSTX.” Nuclear Fusion, vol. 54, no. 8, Aug. 2014. Scopus, doi:10.1088/0029-5515/54/8/083021.
Gerhardt SP, Canik JM, Maingi R, Battaglia D, Bell RE, Guttenfelder W, Leblanc BP, Smith DR, Yuh H, Sabbagh S. Progress in understanding the enhanced pedestal H-mode in NSTX. Nuclear Fusion. 2014 Aug 1;54(8).
Journal cover image

Published In

Nuclear Fusion

DOI

EISSN

1741-4326

ISSN

0029-5515

Publication Date

August 1, 2014

Volume

54

Issue

8

Related Subject Headings

  • Fluids & Plasmas
  • 5106 Nuclear and plasma physics
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics