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Edge Transport Control with the Local Island Divertor and Recent Progress in LHD

M. Kobayashi, N. Ohyabu, T. Mutoh, R. Kumazawa, Y. Feng, M. Shoji, T. Morisaki, S. Masuzaki, A. Sagara, R. Sakamoto, T. Seki, J. Miyazawa, T. Watanabe, M. Goto, K. Ideda, H. Kasahara, S. Morita, B. J. Peterson, N. Ashikawa, K. Saito, S. Sakakibara, T. Tokuzawa, Y. Nakamura, K. Narihara, I. Yamada, H. Yamada, A. Komori, O. Motojima, LHD Experimental Group

Fusion Science and Technology / Volume 52 / Number 3 / October 2007 / Pages 566-573

Technical Paper / The Technology of Fusion Energy - High Heat Flux Components /

The divertor performance of LHD is studied for the two configurations, LID and HD. It is shown that the both divertor configurations play important roles for obtaining high performance plasmas in LHD: the large pumping capability of the LID to keep the low edge density in the IDB-SDC plasma, the large wetted area and the flexibility of strike point sweep of HD to reduce the power load on the divertor plates in long pulse operations. The possible effect of the ergodic layer on impurity retention in divertor is discussed by using the 3D edge transport modelling. It is found that the drag force exerted by the plasma flow can dominate over the thermal force, providing the impurity retention effect. The further changes needed to improve the current divertor configurations are discussed. New divertor designs for the future upgrade of LHD and for a LHD-type reactor are presented.

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