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Author(s):
K. Toi, K.N. Sato, Y. Hamada, S. Ohdachi, H. Sakakita, A. Nishizawa, A. Ejiri, K. Narihara, H. Kuramoto, Y. Kawasumi, S. Kubo, T. Seki, K. Kitachi, J. Xu, K. Ida, K. Kawahata, I. Nomura, K. Adachi, R. Akiyama, A. Fujisawa, J. Fujita, N. Hiraki, S. Hidekuma, S. Hirokura, H. Idei, T. Ido, H. Iguchi, K. Iwasaki, M. Isobe, O. Kaneko, Y. Kano, M. Kojima, J. Koog, R. Kumazawa, T. Kuroda, J. Li, R. Liang, T. Minami, S. Morita, K. Ohkubo, Y. Oka, S. Okajima, M. Osakabe, Y. Sakawa, M. Sasao, K. Sato, T. Shimpo, T. Shoji, H. Sugai, T. Watari, I. Yamada and K. Yamauti
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Title:
Studies of Perturbative Plasma Transport, Ice Pellet Ablation and Sawtooth Phenomena in the JIPP T-IIU Tokamak
Date of publication:
Sep. 1996
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Key words:
Tokamak, Perturbative Plasma Transport, Nonlocal Electron Heat Transport, Pettet Ablation, Sawtooth Crash, Heavy Ion Beam Probe
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Abstract:
ln the JIPP T-IIU tokamak edge cooling imposed by positive biasing of an inserted electrode and injection of a small ice pellet induces an alrnost instantaneous increase in the electron temperature near the center. Rapid current ramp-up increases electron temperature at the edge. Thus produced hot front quickly propagates toward the center, although the toroidal current density increased by the ramp-up is still confined in the edge region of r/a geq 0.7. Rapid current ramp-up also induces a small but sudden drop of the central electron temperature which takes place at much earlier time than the current penetration. The results from cold pulse and current ramp-up experiments suggest nonlocal electron heat transport. A long helical shape ("tail") of ablation light is observed when an ice pellet is injected on-axis(horizontal) and slightly upward or downward off-axis. The direction of the tail is found to be closely related to plasma rotation. Plasma potential and density profile are widely controlled by changing the injection angle of a pellet and pellet size. Radial profiles of particle diffusion coefficient and inward convection velocity are derived from time evolution of density profiles realized by the pellet injection. Rapid potential change is observed during sawtooth crash by a heavy ion beam probe (HIBP). This potential change is caused by combination between arnbipolar electric field and rapid MHD motion across the magnetic field. However, poloidal magnetic flux near the sawtooth inversion radius measured by HIBP hardly changes at the crash. A multichannel motional stark effect polarimeter has revealed that the safety factor at the plasma center becomes well below unity, i.e., 0.7-0.8 during sawtoothing phase. These results suggest a partial reconnection takes place at the sawtooth crash.
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