[Table of Contents]

Plasma and Fusion Research

Volume 1, 045 (2006)

Regular Articles

Characteristics of Radiating Collapse at the Density Limit in the Large Helical Device
Byron J. PETERSON , Junichi MIYAZAWA, Kiyohiko NISHIMURA, Suguru MASUZAKI, Yoshio NAGAYAMA, Nobuyoshi OHYABU, Hiroshi YAMADA, Kozo YAMAZAKI, Takako KATO, Izumi MURAKAMI, Naoko ASHIKAWA, Yuhong XU1), Artem Y. KOSTRIOUKOV2), Yi LIU3), Ryuichi SAKAMOTO, Motoshi GOTO, Kazumichi NARIHARA, Masaki OSAKABE, Kenji TANAKA, Tokihiko TOKUZAWA, Mamoru SHOJI, Hisamichi FUNABA, Shigeru MORITA, Tomohiro MORISAKI, Osamu KANEKO, Kazuo KAWAHATA, Akio KOMORI, Shigeru SUDO, Osamu MOTOJIMA and the LHD Experiment Group
National Institute for Fusion Science
1)
Forschungszentrum Jülich
2)
St. Petersburg Technical University
3)
Southwest Institute of Physics
(Received 24 January 2006 / Accepted 19 June 2006 / Published 29 September 2006)

Abstract

Steady state densities of up to 1.6 × 1020 m-3 have been sustained using gas puff fuelling and NBI heating up to 11 MW in the Large Helical Device (LHD). The density limit in LHD is observed to be greater than 1.6 times the Sudo limit. The density is ultimately limited by a radiating collapse which is attributed to the onset of a radiative thermal instability of the light impurities in the edge region of the plasma based on several recent observations in LHD. First of all the onset of the radiative thermal instability is tied to a certain edge temperature threshold. Secondly, the onset of the thermal instability occurs first in oxygen and then carbon as expected from their cooling rate temperature dependencies. Finally, radiation profiles show that as the temperature drops and the plasma collapses the radiating zone broadens and moves inward. In addition, comparison of impurity lines with the total radiated power behaviour suggests that carbon is the dominant radiator. Two dimensional tomographic inversions of Absolute eXtreme UltraViolet Diode (AXUVD) array data and comparison of modelling with images of radiation brightness from imaging bolometers indicate that the poloidal asymmetry which accompanies the radiating collapse is roughly toroidally symmetric.

Keywords

Large Helical Device, density limit, radiating collapse, carbon impurity, edge electron temperature, imaging bolometer, poloidal asymmetry

DOI: 10.1585/pfr.1.045

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This paper may be cited as follows:

Byron J. PETERSON , Junichi MIYAZAWA, Kiyohiko NISHIMURA, Suguru MASUZAKI, Yoshio NAGAYAMA, Nobuyoshi OHYABU, Hiroshi YAMADA, Kozo YAMAZAKI, Takako KATO, Izumi MURAKAMI, Naoko ASHIKAWA, Yuhong XU, Artem Y. KOSTRIOUKOV, Yi LIU, Ryuichi SAKAMOTO, Motoshi GOTO, Kazumichi NARIHARA, Masaki OSAKABE, Kenji TANAKA, Tokihiko TOKUZAWA, Mamoru SHOJI, Hisamichi FUNABA, Shigeru MORITA, Tomohiro MORISAKI, Osamu KANEKO, Kazuo KAWAHATA, Akio KOMORI, Shigeru SUDO, Osamu MOTOJIMA and the LHD Experiment Group, Plasma Fusion Res. 1, 045 (2006).