Edge localized modes (ELMs) in high-confinement mode plasmas were completely suppressed in KSTAR by applying n=1 nonaxisymmetric magnetic perturbations. Initially, the ELMs were intensified with a reduction of frequency, but completely suppressed later. The electron density had an initial 10% decrease followed by a gradual increase as ELMs were suppressed. Interesting phenomena such as a saturated evolution of edge T(e) and broadband changes of magnetic fluctuations were observed, suggesting the change of edge transport by the applied magnetic perturbations.

Density pumpout and edge-localized mode (ELM) suppression by applied n=2 magnetic fields in low collisionality DIII-D plasmas are shown to be correlated with the magnitude of the plasma response driven on the high field side (HFS) of the magnetic axis, but not the low-field side (LFS) midplane. These distinct responses are a direct measurement of a multi-modal magnetic plasma response, with each structure preferentially excited by a different n=2 applied spectrum and preferentially detected on the LFS or HFS. Ideal and resistive MHD calculations find that the LFS measurement is primarily sensitive to excitation of stable kink modes, while the HFS measurement is primarily sensitive to resonant currents (whether fully shielding or partially penetrated). The resonant currents are themselves strongly modified by kink excitation, with the optimal applied field pitch for pumpout and ELM suppression significantly differing from equilibrium field-alignment.

It is demonstrated that the pitch angle integrals in the transport fluxes in the ν regime calculated in K. C. Shang [Phys. Plasmas 10, 1443 (2003)] are divergent as the trapped-circulating boundary is approached. Here, ν is the collision frequency. The origin of this divergence results from the logarithmic dependence in the bounce averaged radial drift velocity. A collisional boundary layer analysis is developed to remove the singularity. The resultant pitch angle integrals now include not only the original physics of the ν regime but also the boundary layer physics. The transport fluxes, caused by the particles inside the boundary layer, scale as ν.

Abstract. Non-linear reduced MHD modelling of the response of a toroidally rotating plasma on Resonant Magnetic Perturbations (RMPs) is presented for DIII-D and ITER typical parameter. The non-linear cylindrical reduced MHD (RMHD) code was adapted to take into account toroidal rotation and plasma braking mechanisms such as resonant braking (~jxB) and the Neoclassical Toroidal Viscosity (NTV) calculated for low collisionality regimes ("1/ν" and "ν"). It was demonstrated that magnetic flux perturbation can be effectively screened by toroidal plasma rotation. This screening is larger for stronger rotation (V tor ) and lower resistivity In present modelling the central islands are screened by rotation. The pedestal region (r>0.9) is expected to be ergodic both for DIII-D and ITER parameters. Characteristic time for island formation at zero rotation increases for lower resistivity and for the pedestal top (r~0.9) is roughly estimated ~50ms for DIII-D and ~1500ms for ITER The non-resonant helical harmonics ( / q m n ≠ ) do not produce magnetic islands, penetrate on Alfven-like time, are not screened by plasma rotation, but produce NTV. If the "1/ν" low collisionality NTV regime is dominant in ITER, as it is suggested by dedicated DIII-D experiments and modelling, a counter (with respect to the plasma current direction ) rotation is predicted for ITER.

An extensive study of intrinsic and controlled non-axisymmetric field (δB) impacts in KSTAR has enhanced the understanding about non-axisymmetric field physics and its implications, in particular, on resonant magnetic perturbation (RMP) physics and power threshold (Pth) for L–H transition. The n  =  1 intrinsic non-axisymmetric field in KSTAR was measured to remain as low as δB/B0 ~ 4  ×  10−5 even at high-beta plasmas (βN ~ 2), which corresponds to approximately 20% below the targeted ITER tolerance level. As for the RMP edge-localized-modes (ELM) control, robust n  =  1 RMP ELM-crash-suppression has been not only sustained for more than ~90 τE, but also confirmed to be compatible with rotating RMP. An optimal window of radial position of lower X-point (i.e. Rx  =   m) proved to be quite critical to reach full n  =  1 RMP-driven ELM-crash-suppression, while a constraint of the safety factor could be relaxed (q95  =  5 0.25). A more encouraging finding was that even when Rx cannot be positioned in the optimal window, another systematic scan in the vicinity of the previously optimal Rx allows for a new optimal window with relatively small variations of plasma parameters. Also, we have addressed the importance of optimal phasing (i.e. toroidal phase difference between adjacent rows) for n  =  1 RMP-driven ELM control, consistent with an ideal plasma response modeling which could predict phasing-dependent ELM suppression windows. In support of ITER RMP study, intentionally misaligned RMPs have been found to be quite effective during ELM-mitigation stage in lowering the peaks of divertor heat flux, as well as in broadening the ‘wet’ areas. Besides, a systematic survey of Pth dependence on non-axisymmetric field has revealed the potential limit of the merit of low intrinsic non-axisymmetry. Considering that the ITER RMP coils are composed of 3-rows, just like in KSTAR, further 3D physics study in KSTAR is expected to help us minimize the uncertainties of the ITER RMP coils, as well as establish an optimal 3D configuration for ITER and future reactors.