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Author(s):
K. Toi, S. Morita, K. Kawahata, K. Ida, T. Watari, R. Kumazawa, A. Ando, Y. Oka, K. Ohkubo, Y. Hamada, K. Adati, R. Akiyama, S. Hidekuma, S. Hirokura, O. Kaneko, T. Kawamoto, Y. Kawasumi, M. Kojima, T. Kuroda, K. Masai, K. Narihara, Y. Ogawa, S. Okajima, M. Sakamoto, M. Sasao, K. Sato, K. N. Sato, T. Seki, F. Shimpo, S. Tanahashi, Y. Taniguchi, T. Tsuzuki
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Title:
New Features of L-H Transition in Limiter H-Modes of JIPP T-IIU
Date of publication:
Sep. 1992
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Key words:
L-H Transition, Edge Localized Modes, Preceding ELM, m=3/n=1 Magnetic Fluctuations, Edge Radial Electric Field, Poloidal Rotation, Resistive Tearing Mode, Detached Toroidal Current Density Profile
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Abstract:
In limiter H-modes of JIPP T-IIU, a new type of L-H transition preceded by an ELM is observed. The preceding ELM ( pre-ELM ) appears just prior to the L-H transition. This type of transition is usually observed in H-modes of JIPP T-IIU. The L-H transition without the pre-ELM is triggered only in the case when a sufficiently large rapid current ramp down is emploied. In H-modes with constant q(a)~3.5-4.5, coherent magnetic oscillations with m=3 /n=1 destabilized during L-phase are further enhanced at the pre-ELM, and suppressed suddenly at the transition. This mode is situated in the region of the transport barrier. Propagation frequency of the m=3/n=1 mode, which may be affected by plasma mass rotation, rises appreciably ( by ~ 10 % ) during H-phase with frequent ELMs, but remains unchanged for at least 200 mu s after the transition. Behaviours of the m=3/n=1 and m=2/n=1 modes are well explained by quasi-linear resistive tearing mode analysis for modelled toroidal current density profiles slightly detached from the limiter. These experimental results suggest that the transition is controlled by the change of a magnetic field structure relating to the modification of a toroidal current density profile near the edge. The possibility for the development of edge radial electric field as a consequence of the transition is discussed.
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