Characterization of coherent magnetic fluctuations in JFT-2M high recycling steady high-confinement mode plasmas

The most important feature of the "high recycling steady" (HRS) high-confinement mode (H-mode) regime in the JFT-2M tokamak [H. Ninomiya, Fusion Science and Technology (2002), Vol. 42, p. 7] is the stationary pedestal condition in the absence of the large edge localized modes (ELMs). Accompanying the HRS H-mode transition, the coherent magnetic fluctuations in the frequency range of the order of 10-100 kHz with significant variation are seen on the magnetic probes at the vessel wall. Above all, two types of edge magnetohydrodynamics (MHD) activities, which have associated toroidal mode number of n=1 and n∼7, respectively, seem to be more important for the HRS H-mode plasmas. To investigate their interaction, bispectral analysis is applied for the magnetic probe data, exhibiting the phase-coupled oscillations between two types of edge MHD activities. Parameter similarities and differences with small ELMs and stationary ELM-free H-mode regimes in other devices are also discussed.