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Role of edge-localized neoclassical tearing modes in quiescent H-mode plasmas in the DIII-D tokamak

Journal Article · · Physics of Plasmas
DOI:https://doi.org/10.1063/5.0137123· OSTI ID:1963014
 [1];  [2];  [2];  [3];  [4];  [1];  [5];  [1];  [1];  [6];  [7]
  1. Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
  2. General Atomics, San Diego, CA (United States)
  3. Max-Plank-Institut fur Plasmaphysik, Garching (Germany)
  4. University of Texas, Austin, TX (United States)
  5. Massachusetts Institute of Technology (MIT), Cambridge, MA (United States)
  6. University of Wisconsin, Madison, WI (United States)
  7. University of California, Davis, CA (United States)
+ Show Author Affiliations
The edge-harmonic oscillations (EHOs) in standard quiescent H-mode (QH-mode) plasmas in DIII-D are consistent with edge-localized neoclassical tearing modes (NTMs) based on nonlinear two-fluid MHD simulations. Using kinetic equilibria constrained by edge profile measurements, the MHD simulations show that the n = 1 NTM and its harmonics can be destabilized at the pedestal top of QH-mode plasma by the edge bootstrap current. The simulations further show that the unstable NTMs can saturate either at small (<2% ψN) or large (>4% ψN) island width depending on the magnitude of the edge bootstrap current, where ψN is the normalized radius in poloidal flux. The onset of the EHO also results in a prompt decrease in the pedestal width and height, consistent with simulation results for the onset of the NTM at the top of the QH-mode pedestal. This suggests that the avoidance of edge-localized modes (ELMs) in QH-mode can be attributed to the enhanced local transport induced by the NTM that is sufficient to prevent the expansion of the pedestal to an unstable width, analogous to the mechanism explored for ELM suppression by resonant magnetic perturbations. Nonlinear MHD simulations scanning the E × B frequency and the ratio of parallel and perpendicular thermal diffusivity (χ|/χ⊥) at the pedestal top show that edge-localized NTMs are destabilized for conditions of high E × B frequency, high pedestal temperature, and low pedestal density, qualitatively consistent with experimental conditions required for observing the EHO.
Research Organization:
General Atomics, San Diego, CA (United States); Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Fusion Energy Sciences (FES)
Grant/Contract Number:
AC02-09CH11466; FC02-04ER54698; FG02-08ER54999; FG02-97ER54415; FG02-99ER54531; SC0014264
OSTI ID:
1963014
Alternate ID(s):
OSTI ID: 1958081
Journal Information:
Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 2 Vol. 30; ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English

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