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

Abstract

High-triangularity ELMy H-mode experiments (δx~0.45) have been carried out in JT-60U. In the low-density regime (n̄e/nGW<0.5), the discharges are characterized by type-I ELMs and high-triangularity plasmas produced higher H-mode pedestal pressure than low-triangularity plasmas (δx~0.20). In the high-density regime (n̄e/nGW>0.5), at fixed neutral beam heating power type-III ELMs are generated and the pedestal pressure reduces gradually with density whereas the ELM frequency at low triangularity is much lower at a given density. Compared to low-triangularity plasmas at low densities, higher pedestal temperature was obtained at high triangularity and the core temperature was also improved by almost the same factor. The profiles of temperature are stiff in the sense that there seems to exist a minimum scale length of temperature gradient. Since plasma shaping affects strongly the peripheral region of toroidal magnetic flux surfaces, the improvement of the edge stability by triangularity leads to higher pedestal temperature, which in turn raises the core temperature.