Experimental characterization of the quasi-coherent mode in EDA H-Mode and QCE scenarios at ASDEX Upgrade

the EUROfusion MST1 Team, the ASDEX Upgrade Team

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The quasi-coherent mode (QCM), appearing in enhanced D α high confinement mode (EDA H-mode) and quasi-continuous exhaust (QCE) plasmas has been analysed in detail at ASDEX Upgrade via thermal helium beam spectroscopy under various discharge parameters. In both scenarios the QCM appears to be localized close to the separatrix and to propagate in ion diamagnetic direction in the plasma frame. The poloidal wavenumber of the QCM is about 0.025 < k θ ρ s < 0.075 and the radial wavenumber is k r ≈ 0 cm − 1 . It was found that the plasmas are generally below the ideal MHD limit at the separatrix. All the properties are consistent with ideal, resistive or kinetic ballooning modes. Simultaneous to the appearance of the QCM, higher harmonic modes can be observed in EDA H-modes, which are exclusively visible in magnetic pick-up coils and have toroidal mode numbers of up to n = 10. By performing a bicoherence analysis it was found that the higher harmonic modes and the QCM are coupling, but are disjoint phenomena. Qualitatively, the bandwidth of the QCM serves as a promising distinctive feature between QCE plasmas and EDA H-modes.

Original languageEnglish
Article number016038
JournalNuclear Fusion
Issue number1
StatePublished - Jan 2024


  • EDA H-mode
  • fusion
  • helium beam diagnostic
  • plasma edge
  • plasma modes
  • quasi-coherent mode
  • quasi-continuous exhaust


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