Improvement of Plasma Performance Using Carbon Pellet Injection in Large Helical Device

Shigeru MORITA; Motoshi GOTO; Kenichi NAGAOKA; Chunfeng DONG; Hangyu ZHOU; Zhengying CUI; Yunbo DONG; Xiang GAO; Katsumi IDA; Katsunori IKEDA; Osamu KANEKO; Shiyao LIN; Haruhisa NAKANO; Masaki OSAKABE

Plasma Science and Technology > 2011 > 13(3): 290-296.

Shigeru MORITA, Motoshi GOTO, Kenichi NAGAOKA, Chunfeng DONG, Hangyu ZHOU, Zhengying CUI, Yunbo DONG, Xiang GAO, Katsumi IDA, Katsunori IKEDA, Osamu KANEKO, Shiyao LIN, Haruhisa NAKANO, Masaki OSAKABE. Improvement of Plasma Performance Using Carbon Pellet Injection in Large Helical Device[J]. Plasma Science and Technology, 2011, 13(3): 290-296.

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Improvement of Plasma Performance Using Carbon Pellet Injection in Large Helical Device

1) National Institute for Fusion Science, Toki 509-5292, Gifu, Japan 2) Graduate University for Advanced Studies, Toki 509-5292, Gifu, Japan 3) Southwestern Institute of Physics, Chengdu 610041, China 4) Institute of Plasma Physics Chinese Academy of Sciences, Hefei 230031, China

Funds: This work was partially carried out under the LHD project financial support (NIFS09ULPP527). This work was also partially supported by the JSPS-CAS Core-University program in the field of ‘Plasma and Nuclear Fusion’.

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Abstract

A cylindrical carbon pellet with a size of 1.2L?1.2? to 1.8L?1.8?mm and a velocity of 100 to 300 m/s was injected into Large Helical Device (LHD) for an efficient fueling based on its deeper deposition instead of hydrogen gas puffing and ice pellet injection. Electron density increment of ?ne=1014cm-3 is successfully obtained by single carbon pellet injection without plasma collapse. Typical density and temperature of the ablation plasma of the carbon pellet, e.g., 6.5x1016cm-3 and 2.5eV for CII, are examined respectively by spectroscopic method. A confinement improvement up to 50% compared to ISS-95 stellarator scaling is clearly observed in a relatively low-density regime of ne=2 to 4?1013cm-3, and high ion temperature Ti(0) of about 6keV is also observed with an internal transport barrier at ne=1.2?1013cm-3. In particular, the improvement in the ion temperature largely exceeds that observed in hydrogen gas- puffed discharges, which typically ranges below 3 keV.
- carbon pellet injection,
- confinement improvement,
- high ion temperature

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