The filamentary nature and dynamics of edge-localized modes (ELMs) in the KSTAR high-confinement mode plasmas have been visualized in 2D via electron cyclotron emission imaging. The ELM filaments rotating with a net poloidal velocity are observed to evolve in three distinctive stages: initial linear growth, interim quasisteady state, and final crash. The crash is initiated by a narrow fingerlike perturbation growing radially from a poloidally elongated filament. The filament bursts through this finger, leading to fast and collective heat convection from the edge region into the scrape-off layer, i.e., ELM crash.

In the quiescent H-mode (QH-mode) regime, edge harmonic oscillations (EHO) play an important role in avoiding transient edge localized mode (ELM) power fluxes by providing benign and continuous edge particle transport. A detailed theoretical, experimental and modeling comparison has been made of low-n (n≤5) EHO in DIII-D QH-mode plasmas. The calculated linear eigenmode structure from the extended MHD code M3D-C1 matches closely the coherent EHO properties from external magnetics data and internal measurements using the ECE, BES, ECE-Imaging and microwave imaging reflectometer (MIR) diagnostics, as well as the kink/peeling mode properties found by the ideal MHD code ELITE. Numerical investigations indicate that the low-n EHO-like solutions from M3D-C1 are destabilized by the rotation and/or rotational shear while high-n modes are stabilized. This effect is independent of the rotation direction, suggesting that EHO can be destabilized in principle with rotation in either direction. The modeling results are consistent with observations of the EHO, support the proposed theory of the EHO as a low-n kink/peeling mode destabilized by edge ExB rotational shear, and improve our understanding and confidence in creating and sustaining QHmode in present and future devices.

The ECE imaging ͑ECEI͒ diagnostic tested on the TEXTOR tokamak revealed the sawtooth reconnection physics in unprecedented detail, including the first observation of high-field-side crash and collective heat transport ͓H. K. Park, N. C. Luhmann, Jr., A. J. H. Donné et al., Phys. Rev. Lett. 96, 195003 ͑2006͔͒. An improved ECEI system capable of visualizing both high-and low-field sides simultaneously with considerably better spatial coverage has been developed for the KSTAR tokamak in order to capture the full picture of core MHD dynamics. Direct 2D imaging of other MHD phenomena such as tearing modes, edge localized modes, and even Alfvén eigenmodes is expected to be feasible. Use of ECE images of the optically thin edge region to recover 2D electron density changes during L/H mode transitions is also envisioned, providing powerful information about the underlying physics. The influence of density fluctuations on optically thin ECE is discussed.

Different combinations of on-axis and off-axis neutral beams are injected into DIII-D plasmas that are unstable to reversed shear Alfvén eigenmodes (RSAE) and toroidal Alfvén eigenmodes (TAE). The variations alter the classically expected fast-ion gradient ∇β f in the plasma interior. Off-axis injection reduces the amplitude of RSAE activity an order of magnitude. Core TAEs are also strongly stabilized. In contrast, at larger minor radius, the fast-ion gradient is similar for on-and off-axis injection and switching the angle of injection has a weaker effect on the stability of TAEs. The average mode amplitude correlates strongly with the classically expected profile but the measured profile relaxes to similar values independent of the fraction of off-axis beams. The observations agree qualitatively with a 'critical-gradient' model of fast-ion transport.

The installation of a 2D electron cyclotron emission imaging (ECEI) diagnostic on ASDEX Upgrade has provided a new means to observe the nature of Edge Localized Modes (ELMs). For a series of ELMs in a typical type-I ELMy H-mode (with q 95 = 4.7), the 2D dynamics have been characterized. Firstly, a clear distinction between so-called 'fast' and 'slow' ELMs was found to be the occurrence of an off-mid-plane fluctuation in case of the latter. This mode has its amplitude strongest off-midplane and its poloidal and toroidal mode numbers are m ~ 110 and n ~ 30. Secondly, prior to the onset of the ELM's temperature collapse, a mode is observed that covers the whole ECEI observation window. Here, the estimated poloidal and toroidal mode numbers are m ~ 75 and n ~ 20. These have been seen to increase towards the ELM crash, simultaneously with a velocity increase of the mode (in poloidal direction). Finally, filaments have been identified during the temperature collapse phase and their motion could be followed in the vertical direction. Contrary to both the off-mid-plane fluctuation and the ELM onset mode, which only have been seen rotating in the electron diamagnetic drift direction, the first few filaments have sometimes been observed to move in the opposite direction as well.