NIFS-572

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Author(s):

M. Fujiwara, H. Yamada, A. Ejiri, M. Emoto, H. Funaba, M. Goto, K. Ida, H. Idei, S. Inagaki, S. Kado, O. Kaneko, K. Kawahata, A. Komori, S. Kubo, R. Kumazawa, S. Masuzaki, T. Minami, J. Miyazawa, T. Morisaki, S. Morita, S. Murakami, S. Muto, T. Muto, Y. Nagayama, Y. Nakamura, H. Nakanishi, K. Narihara, K. Nishimura, N. Noda, T. Kobuchi, S. Ohdachi, N. Ohyabu, Y. Oka, M. Osakabe, T. Ozaki, B. J. Peterson, A. Sagara, S. Sakakibara, R. Sakamoto, H. Sasao, M. Sasao, K. Sato, M. Sato, T. Seki, T. Shimozuma, M. Shoji, H. Sazuki, Y. Takeiri, K. Tanaka, K. Toi, T. Tokuzawa, K. Tsumori, I. Yamada, S. Yamaguchi, M. Yokoyama, K.Y. Watanabe, T. Watari, R. Akiyama, H. Chikaraishi, K. Haba, S. Hamaguchi, M. Iima, S. Imagawa, N. Inoue, K. Iwamoto, S. Kitagawa, Y. Kubota, J. Kodaira, R. Maekawa, T. Mito, T. Nagasaka, A. Nishimura, Y. Takita, C. Takahashi, K. Takahata, K. Yamauchi, H. Tamura, T. Tsuzuki, S. Yamada, N. Yanagi, H. Yonezu, Y. Hamada, K. Matsuoka, K. Murai, K. Ohkubo, I. Ohtake, M. Okamoto, S. Sato, T. Satow, S. Sudo, S. Tanahashi, K. Yamazaki, O. Motojima and A. Iiyoshi

Title:

Plasma Confinement Studies in LHD

Date of publication:

Oct. 1998

Key words:

IAEA, fusion energy conference, Yokohama

Abstract:

The initial experiments of the Large Helical Device (LHD) have extended confinement studies on currentless plasmas to a large scale (R=3.9 m, a = 0.6 m). Heating by NBI of 3 MW has produced plasmas with a fusion triple product of 8 x 10^18 keVm^-3s at a magnetic field of 1.5T. An electron temperature of 1.5 keV and an ion temperature of l.1 keV have been achieved simultaneously at the line-averaged electron density of 1.5 x 10^19 m^-3. The maximum stored energy has reached 0.22 MJ with neither unexpected confinement deterioration nor visible MHD instabilities, which corresponds to <beta> =0.7%. Energy confinement times, reaching 0.17 s at the maximum, have shown a manner similar to the present scaling law derived from the existing medium sized helical devices, but improve on it by 50%. A distinguishing feature of a favorable dependence of energy confinement time on density remains in the present power density (~40kW/m^3) and the electron density (3x 10^19m^-3) regimes unlike L-mode in tokamaks. Temperatures of both electrons and ions as high as 200 eV have been observed at the outermost flux surface, which indicates a qualitative jump in performance from the helical devices to date. Spontaneously generated toroidal currents agree with the physical picture of neoclassical bootstrap currents. Change of magnetic configuration due to finite-beta eff'ect has been well described by the 3-D MHD equilibrium analysis. An escape of particles from the core region leading to a hollow density profile has been observed in hydrogen plasmas, which is mitigated through core fueling with a pellet injection or in helium discharges.

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