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Author(s):
S. Masuzaki et al.
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Title:
Particle Balance Study in the Large Helical Device
Date of publication:
Oct. 2006
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Key words:
21 IAEA Fusion Energy Conference , EX/P4-15
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Abstract:
In the Large Helical Device (LHD), plasma experiments with an intrinsic helical divertor (HD) and a local island divertor (LID) have been performed, respectively. The HD is an open divertor at this stage, and the LID is a closed divertor equipping a baffle structure and a pump-system. Particle balance study has been conducted in these two divertor configurations. In the LID configuration, the substantial part of fuelled particles is evacuated during discharge. On the other hand, in the HD configuration, the most part of fuelled particles are retained in the vacuum vessel. Therefore the discharge history strongly affects the density control in the HD configuration. The difference in the neutral particle behavior between the HD and the LID configurations is considered to be explained by following conditions in the LID configuration: (1) The low charge exchange particle flux to the first wall due to the relatively low edge neutral density reduces the amount of implantation of the neutral particles in the first wall. (2) The small carbon amount released by physical and chemical sputtering from the helical divertor plates due to the small ion flux to the plates in the LID configuration leads the co-deposited particles to be small. (3) For the high operational temperature (over 1000 K) of the LID divertor plates in the LID configuration, the amount of retained particle in the plates is small. On the contrary, in the HD configuration, the operational temperature of the helical divertor plates is typically less than 600K, and it is too low for the particle desorption from the carbon divertor plates.
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