Reduction of core turbulence in I-mode plasmas in Alcator C-Mod

A. E. White, M. Barnes, A. Dominguez, M. Greenwald, N. T. Howard, A. E. Hubbard, J. W. Hughes, D. R. Mikkelsen, F. I. Parra, M. L. Reinke, C. Sung, J. Walk, D. G. Whyte

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12 Scopus citations

Abstract

In this paper, we report observations of reduced core (0.40<ρ<0. 95) fluctuations in the edge localized mode (ELM)-free high-confinement regime, I-mode, at Alcator C-Mod (Marmar et al2009 Nucl. Fusion 49 104014). Long wavelength (kθρs<0.5) density fluctuation levels are observed to decrease from L-mode levels by up to 30% in I-mode, while long wavelength (kθρs<0.3) electron temperature fluctuation levels are observed to decrease by up to 70% in I-mode. This reduction in core turbulence is correlated with the increases in confinement in I-mode compared to L-mode. As the pedestal temperature increases across the L-I transition, core density fluctuations (0.40<ρ<0.95) are reduced prior to the onset of the edge-localized (ρ∼0.99-1.0) weakly coherent mode (WCM) and prior to the reduction of low-frequency (ρ∼0.99-1.0) turbulence in the edge/pedestal region. This result helps add to our understanding of the dynamics of confinement transitions such as I-mode and H-mode, where changes in edge turbulence are more typically observed to occur prior to changes in core turbulence.

Original languageEnglish (US)
Article number083019
JournalNuclear Fusion
Volume54
Issue number8
DOIs
StatePublished - Aug 1 2014
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Nuclear and High Energy Physics
  • Condensed Matter Physics

Keywords

  • H-mode
  • I-mode
  • confinement transition
  • core transport
  • core turbulence
  • edge turbulence

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