Pedestal Structure and Thermal Energy Confinement of ELMy H-mode in JT-60U
Hajime Uranoa, Yutaka Kamadab, Hiroshi Shiraib, Tomonori Takizukab, Takeshi Fukudab, Takaki Hataeb, Shunsuke Ideb and Takaaki Fujitab
a) Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan
b) Naka Fusion Research Establishment, Japan Atomic Energy Research Institute, Naka-gun, Ibaraki 311-0193, Japan
Abstract.
Degradation of the thermal energy confinement with an increase in plasma density is a serious problem in ITER with a high density operation. In this study, the thermal energy confinement properties are analyzed by separating the core and pedestal components and the role of the edge pedestal structure imposed by the destabilization of ELMs on the thermal energy confinement of the core plasma is discussed in JT-60U ELMy H-mode plasmas.
As the density is raised in type-I ELM regime, the temperature at the shoulder of the H-mode pedestal is reduced so that the pedestal pressure remains almost constant for fixed Ip, Bt, and plasma shape. The core component also tends to remain almost constant over wide range of density. The enhancement factor of the core confinement based on the offset non-linear scaling [1], which is determined by the gyro-Bohm-like transport, remarkably decreases with density. Basiders, at a high density, the effective thermal conductivity of the core component tends to increase as the pedestal temperature decreases [2]. Thus, in a high density regime, an increase in plasma density due to strong gas puffing reduces the pedestal temperature due to the action of type-I ELMs and brings about the deterioration of the core energy confinement. One observes an increase in the density where confinement degradation sets in with increasing triangularity because the pedestal pressure is increased with triangularity. In high triangularity discharges, the pedestal temperature becomes higher and the higher energy confinement of the core plasma can be obtained at a given pedestal density.
References
[1] T. Takizuka: Plasma Phys. Control. Fusion 40 (1998) 851.
[2] H. Urano et al.: submitted to Plasma Phys. Control. Fusion