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High Power Heating and Steady State Operation in the Large Helical Device

T. Mutoh, K. Nagaoka, H. Takahashi, H. Kasahara, M. Osakabe, S. Kubo, T. Shimozuma, Y. Yoshimura, K. Tsumori, T. Seki, K. Saito, H. Igami, H. Nakano, K. Ikeda, M. Kisaki, R. Seki, S. Kamio, T. Ii, Y. Nakamura, Y. Takeiri, O. Kaneko, LHD Experiment Group

Fusion Science and Technology / Volume 68 / Number 2 / September 2015 / Pages 216-224

Technical Paper / Proceedings of TOFE-2014 / dx.doi.org/10.13182/FST15-120

First Online Publication:June 26, 2015
Updated:August 31, 2015

Recent advances in the high power and steady state heating system and experiment results of the Large Helical Device (LHD) are reviewed in this paper. Plasma performance is extended largely through high power NBI, ECH and steady state ICRF heating devices, and improved operation techniques. The NBI of a 28 MW has extended the plasma parameter regime such as ion ITB plasmas, has a central ion temperature of more than 8 keV, and the extremely high-density plasmas ten times higher than the tokamak limit. An ECH system with seven gyrotrons (total power of 4.6MW) has been operated for pre-ionization and plasma heating. The high electron temperature regime was extended toward a higher density regime and a central electron temperature of 13.5 keV was achieved with a line-averaged electron density of ne = 1 x 1019 m-3. Steady state operation plasma with ne =  1.2 x 1019 m-3, ion and electron temperature of 2 keV, and plasma sustainment time of 48 min was achieved with ICH and ECH heating power of 1.2 MW for majority helium with minority hydrogen.