Particle confinement and transport in JT-60U

Abstract

Particle confinement and transport have been systematically analysed for improved confinement modes in JT-60U. A scaling law for the total number of ions in the main plasma of ELMy H mode plasmas was proposed for the first time, with confinement times of the particles fuelled by NBI (centre fuelling) and by recycling and gas puffing (edge fuelling) separately defined. The confinement time increases and decreases with density for centre and edge fuelling, respectively. A comparison between the experimental data and the scaling was made for high βp ELMy H mode and reversed shear plasmas. In the reversed shear plasma, particle confinement was enhanced by a factor of about 2 compared with the scaling, when the enhancement factor of the energy confinement time over the ELMy H mode scaling was larger than 1.2. Density controllability is discussed on the basis of the scaling in ELMy H mode, and it was found that additional fuelling with a confinement time of 0.1-0.4 s is necessary for density control in JT-60U. The particle diffusivity and convection velocity were evaluated by means of a perturbation technique using modulated helium gas puffing in ELMy H mode and reversed shear plasmas. The particle diffusivity and convection velocity were estimated to be 0.2-2 m2/s and from -4 (inward) to 0 m/s for the reversed shear plasma, and 0.4-2 m2/s and from -5.5 (inward) to +2.5 (outward) m/s for the ELMy H mode plasma, respectively. The particle diffusivity around the internal transport barrier was reduced by a factor of 5-6 compared with that in the inside and outside regions in the reversed shear plasma.