The multi-faced nature of the quasicoherent mode in EDA H-mode

Abstract

In order to extend the enhanced D-Alpha H-mode to future devices, it is crucial to understand the properties of the main signature of this regime, the quasicoherent mode (QCM), that likely clamps the pressure gradient below the ideal magnetohydrodynamic limit. The turbulent character of the QCM is investigated with scanning probes in ASDEX Upgrade. Analysis reveals the multi-faced character of the mode that spans both the confined region (where the radial electric field is negative) and the near scrape-off layer (SOL) (where it is positive). Fluctuations of density and potential at the QCM frequency are more anti-correlated towards the confined region, which is a fingerprint of electromagnetic instabilities, while they become more correlated in the SOL, as expected for a drift-wave, inducing cross-field transport across the separatrix.

Keywords

• ELM-free
• quasi-coherent mode
• EDA H-mode
• ASDEX upgrade
• plasma turbulence