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(EXP4/18) Impact of Pellet Injection on Extension of Operational Region in LHD

R. Sakamoto¹⁾, H. Yamada¹⁾, K. Tanaka¹⁾, K. Narihara¹⁾, S. Morita¹⁾, S. Sakakibara¹⁾, S. Masuzaki¹⁾, L. R. Baylor²⁾, P. W. Fisher²⁾, S. K. Combs²⁾, M. J. Gouge²⁾, S. Kato¹⁾, A. Komori¹⁾, O. Kaneko¹⁾, N. Ashikawa³⁾, P. de Vries¹⁾, M. Emoto¹⁾, H. Funaba¹⁾, M. Goto¹⁾, K. Ida¹⁾, H. Idei¹⁾, K. Ikeda¹⁾, S. Inagaki¹⁾, M. Isobe¹⁾, S. Kado¹⁾, K. Kawahata¹⁾, K. Khlopenkov¹⁾, S. Kubo¹⁾, R. Kumazawa¹⁾, T. Minami¹⁾, J. Miyazawa¹⁾, T. Morisaki¹⁾, S. Murakami¹⁾, S. Muto¹⁾, T. Mutoh¹⁾, Y. Nagayama¹⁾, Y. Nakamura¹⁾, H. Nakanishi¹⁾, K. Nishimura¹⁾, N. Noda¹⁾, T. Notake⁴⁾, T. Kobuchi³⁾, Y. Liang³⁾, S. Ohdachi¹⁾, N. Ohyabu¹⁾, Y. Oka¹⁾, M. Osakabe¹⁾, T. Ozaki¹⁾, R. O. Pavlichenko¹⁾, B. J. Peterson¹⁾, A. Sagara¹⁾, K. Saito⁴⁾, H. Sasao³⁾, M. Sasao¹⁾, K. Sato¹⁾, M. Sato¹⁾, T. Seki¹⁾, T. Shimozuma¹⁾, M. Shoji¹⁾, S. Sudo¹⁾, H. Suzuki¹⁾, M. Takechi¹⁾, Y. Takeiri¹⁾, N. Tamura³⁾, K. Toi¹⁾, T. Tokuzawa¹⁾, Y. Torii⁴⁾, K. Tsumori¹⁾, I. Yamada¹⁾, S. Yamaguchi¹⁾, S. Yamamoto⁴⁾, Y. Yoshimura¹⁾, K. Y. Watanabe¹⁾, T. Watari¹⁾, K. Yamazaki¹⁾, Y. Hamada¹⁾, O. Motojima¹⁾, M. Fujiwara^1)
 
1) National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
²⁾ Oak Ridge National Laboratory, PO Box 2009, Oak Ridge, TN 37831-8071, USA
³⁾ Department of Fusion Science, School of Mathematical and Physical Science, Graduate University for Advanced Studies, Hayama, 240-0193, Japan
⁴⁾ Department of Energy Engineering and Science, Nagoya University, 464-8603, Japan

Abstract.  Pellet injection has been used as a primary fueling scheme in Large Helical Device (LHD). Pellet injection has extended an operational region of NBI plasmas to higher densities with maintaining preferable dependence of energy confinement on density, and achieved several important data, such as plasma stored energy (0.88 MJ), energy confinement time (0.3 s), $\beta$ (2.4 % at 1.3 T) and density ( 1.1×10²⁰m^{- 3}). These parameters cannot be attained by gas puffing. Ablation and subsequent behavior of plasma has been investigated. Measured pellet penetration depth that is estimated by duration of the H$\alpha$ emission is shallower than predicted penetration depth from the simple neutral gas shielding (NGS) model. The penetration depth can be explained by NGS model with fast ion effect on the ablation. Just after ablation, redistribution of ablated pellet mass was observed in short time ( $\sim$ 400ms). The redistribution causes shallow deposition and low fueling efficiency.

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