JET radiative mantle experiments in ELMy H-Mode

Abstract

Radiative mantle experiments were performed on JET ELMy H-mode plasmas. The septum configuration was used where the X-point is embedded into the top of the septum. Argon radiated 50% of the input power from the bulk plasma while Z_eff rose from an intrinsic level of 1.5 to about 1.7 due to the injected argon. The total energy content and global energy confinement time decreased 15% when the impurities were introduced. In contrast, the effective thermal diffusivity in the core confinement region (r/a = 0.4-0.8) decreased by 30%. Usually, JET ELMy H-mode plasmas have confinement that is correlated to the edge pedestal pressure. The radiation lowered the edge pedestal and consequently lowered the global confinement. Thus the global confinement was changed by a competition between the edge pedestal reduction lowering the confinement and the weaker RI effect reducing the core transport coefficients. The ELM frequency increased from 10 Hz type-I ELMs, to 200 Hz type-III ELMs. The energy lost by each ELM reduced to 0.5% of the plasma energy content.