Observation of high recycling steady H-mode edge and compatibility with improved core confinement mode on JFT-2M

A new operational regime has been discovered on JFT-2M under the boronized first wall condition to produce High Recycling Steady (HRS) H-mode, which is characterized by good energy confinement (H89p∼1.6) at high density around 70% of the Greenwald density ne/nGW), low radiated power fraction, and the complete disappearance of large (Giant) ELMs. Accompanying the HRS H-mode, a coherent magnetic fluctuation is observed at around 50-150kHz, whose characteristics are similar to the Enhanced Dα (EDA) H-mode reported from Alcator C-Mod. The H'-mode, previously observed on JFT-2M, had common features with EDA-mode in terms of the coherent density fluctuation, but it appeared transiently. The HRS operating regime is also similar to EDA-mode, except that HRS is seen even at low q95 (2<q95≤3). The most important feature of HRS H-mode edge condition is the compatibility with an improved core confinement mode at high density without large ELMs. We have demonstrated that an internal transport barrier (ITB) can be produced with the HRS H-mode edge condition, achieving βNH89p∼6.2 at the ne/nGW ∼70%, transiently. (author)