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Title: Progress in understanding the enhanced pedestal H-mode in NSTX

The 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 behavior 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 10 cm 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 t hermal transport is comparable to or less than anticipated from a simple neoclassical transport model. Cases are shown where EP H-modes were reliably generated, through these low-q95 examples were difficult to sustain. A case where an externally triggered ELM precipitates themore » transition to EP H-mode is also shown, though an initial experiment designed to trigger EP-H-modes in this fashion was successful.« less
Authors:
 [1] ;  [2] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [3] ;  [4] ;  [5]
  1. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Univ. of Wisconsin, Madison, WI (United States) Dept. of Engineering Physics
  4. Nova Phontonics, Princeton, NJ (Unitied States)
  5. Columbia Univ., New York, NY (United States) Dept. of Applied Physics
Publication Date:
OSTI Identifier:
1164217
Report Number(s):
PPPL-5031
Journal ID: ISSN 0029-5515; PPPL-5031
Grant/Contract Number:
AC02-09CH11466
Type:
Accepted Manuscript
Journal Name:
Nuclear Fusion
Additional Journal Information:
Journal Volume: 54; Journal Issue: 8; Journal ID: ISSN 0029-5515
Publisher:
IOP Science
Research Org:
Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY EP H--MODE; H--MODE; NSTX; SPHERICAL TORUS