K. Toi, F. Watanabe, K. Tanaka, T. Tokuzawa, K. Ogawa, M. Isobe, M. Osakabe, Y. Suzuki, T. Akiyama, K. Ida, M. Goto, K. Kawahata, T. Morisaki, S. Morita, K. Narihara, S. Ohdachi, S. Sakakibara, H. Urano, I. Yamada, M. Yoshinuma and LHD Experiment Group
Role of Low-Order Rational Surfaces in Transport Barrier
Date of publication:
22 IAEA Fusion Energy Conference, PD/P-01
In the Large Helical Device, edge transport barrier (ETB) was formed by H-mode transition near the low-order rational surfaces, that is, at the iota/2pi=1 resonant layer (iota/2pi: the rotational transform) in outward-shifted plasmas of R_ax=3.9m (R_ax: the magnetic axis position in the vacuum field), and the iota/2pi=2 resonant layer in inward-shifted plasmas of R_ax=3.6m. The iota/2pi=1 and 2 resonant layers reside in the stochastic field region existing just outside the last closed magnetic surface (LCFS). In the outward-shifted plasmas, H-modes without edge localized modes (ELM-free H-modes) followed by giant ELMs were obtained, while H-modes with high frequency and low amplitude ELMs were obtained in the inward-shifted plasmas. A new type of barrier formation induced by TAE bursts was observed in the plasmas of R_ax=3.6m, where the transport barrier is formed near the iota/2pi=1 surface locates inside LCFS.