Thermal energy confinement properties of ELMy H mode plasmas in JT-60U

The dominant causes of the reduction in the enhancement factor of thermal energy confinement with increasing plasma density in ELMy H mode plasmas in JT-60U were analysed by separating the thermal stored energy into core and pedestal components. The enhancement factor of the core confinement evaluated by the offset non-linear scaling which was developed in the ITER H mode confinement database decreased significantly with increasing density, while the pedestal component remained almost constant over a wide range of density. The influence of the edge pedestal structure imposed by the destabilization of type I ELMS on thermal energy confinement of the core plasma was also quantitatively clarified. As the density increased, the saturation of the pressure at the pedestal shoulder, p(ped), caused by the type I ELM activities forced a reduction in the pedestal temperature. The core temperature for each species, in turn, decreased only by an approximately constant factor with a reduction in the pedestal temperature, resulting in the saturation of the thermal stored energy in the high density regime.