The pressure at the top of the edge transport barrier (or "pedestal height") strongly impacts fusion performance, while large Edge Localized Modes (ELMs), driven by the free energy in the pedestal region, can constrain material lifetimes. Accurately predicting the pedestal height and ELM behavior in ITER is an essential element of prediction and optimization of fusion performance. Investigation of intermediate wavelength MHD modes (or "peeling-ballooning" modes) has led to improved understanding of important constraints on the pedestal height and the mechanism for ELMs. The combination of high resolution pedestal diagnostics, including substantial recent improvements, and a suite of highly efficient stability codes, has made edge stability analysis routine on several major tokamaks, contributing both to understanding, and to experimental planning and performance optimization. Here we present extensive comparisons of observations to predicted edge stability boundaries on several tokamaks, both for the standard (Type I) ELM regime, and for small ELM and ELM-free regimes. We further use the stability constraint on pedestal height to test models of the pedestal width, and self-consistently combine a simple width model with peeling-ballooning stability calculations to develop a new predictive model (EPED1) for the pedestal height and width. This model is tested against experimental measurements, and used in initial predictions of the pedestal height for ITER.

A global gyrokinetic toroidal full-f five-dimensional Vlasov simulation GT5D (Idomura et al 2008 Comput. Phys. Commun. 179 391)is extended including sources and collisions. Long time tokamak micro-turbulence simulations in open system tokamak plasmas are enabled for the first time based on a full-f gyrokinetic approach with self-consistent evolutions of turbulent transport and equilibrium profiles. The neoclassical physics is implemented using the linear Fokker-Planck collision operator, and the equilibrium radial electric field E r is determined self-consistently by evolving equilibrium profiles. In ion temperature gradient driven turbulence simulations in a normal shear tokamak with on-axis heating, key features of ion turbulent transport are clarified. It is found that stiff ion temperature T i profiles are sustained with globally constant L ti ≡ |T i /T i | near a critical value, and a significant part of the heat flux is carried by avalanches with 1/f type spectra, which suggest a self-organized criticality. The E r shear strongly affects the directions of avalanche propagation and the momentum flux. Non-diffusive momentum transport due to the E r shear stress is observed and a non-zero (intrinsic) toroidal rotation is formed without momentum input near the axis.

The plasma rotation necessary for stabilization of resistive-wall modes (RWMs) is investigated by controlling the toroidal plasma rotation with external momentum input by injection of tangential neutral beams. The observed threshold is 0.3% of the Alfvén velocity and much smaller than the previous experimental results obtained with magnetic braking. This low critical rotation has a very weak beta dependence as the ideal wall limit is approached. These results indicate that for large plasmas such as in future fusion reactors with low rotation, the requirement of the additional feedback control system for stabilizing RWM is much reduced.

This paper reports the progress made at JET-ILW on integrating the requirements of the reference ITER baseline scenario with normalised confinement factor of 1, at a normalised pressure of 1.8 together with partially detached divertor whilst maintaining these conditions over many energy confinement time. The 2.5MA high triangularity ELMy H-modes are studied with two different divertor configurations. The power load reduction with N seeding is reported. The relationship between an increase in energy confinement and pedestal pressure with triangularity is investigated. The operational space of both plasma configurations is studied together the ELM energy losses and stability of the pedestal of unseeded and seeded plasmas.

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