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Edge transport study of LID configuration in LHD with 3D Monte Carlo codes of plasma & neutral transport
M. Kobayashi1), Y. Feng2), D. Reiter3), T. Morisaki1), S. Masuzaki1), F. Sardei2), T. Hayashi1)
1)National Institute for Fusion Science, Toki, Gifu 509-5292, Japan
Edge transport physics of the Local Island Divertor (LID) configuration in LHD is studied with the 3D transport code package, EMC3-EIRENE. EMC3 [1] solves plasma fluid equations of mass, momentum and energy with a Monte Carlo scheme, while EIRENE [2] solves a kinetic neutral transport equation also with a Monte Carlo scheme. The two codes are iteratively coupled, and are capable to deal with an almost arbitrarily complex 3D geometry of magnetic field and plasma facing components. This is a big advantage of studying an interaction between plasma and neutrals in self-consistent manner especially because flight trajectories of neutrals strongly depend on the 3D shape of the divertor and baffle (pump duct). In the present computation, the following atomic/molecular processes are taken into account: Ionization (2.1.5) [3] and relevant excitation & radiative decay. Resonant charge exchange (CX) (3.1.8) [3] (implicitly accounting for the elastic component). For molecules, the six default processes of EIRENE (2.2.5, 2.2.9, 2.2.10, 2.2.11, 2.2.12, 2.2.14) [3] are treated. The initial sources of the neutrals are distributed on the divertor surface, and are chosen proportional to the plasma particle deposition pattern. With a corresponding input power of 1.4 MW and an up-stream density of 1.2x1019 m-3, we found a rather high density (up to ~ 1020 m-3) and low temperature (~ a few eV) plasma in the divertor. This is attributed to the closed structure of the divertor and pump duct, which leads to a strong interaction between the plasma and the neutrals. It was found that the energy loss via neutrals becomes several tens percent of the total input power, and that depending on the shape of the LID head, the results indicate a transition to plasma detachment. The computational studies are still ongoing, and a few additional collisional processes, which are expected to become significant in such dense and cold plasma, are presently being activated in the runs. At the conference, these latest results on their relevance will be also reported.
References
[1] Y. Feng et al., Contrib. Plasma Phys. 44 (2004) pp. 57-69.
[2] D. Reiter, Technical Report Jul-1947, KFA Juelich, Germany (1984), and www.eirene.de (2004). [3] R.K. Janev, et al., Elementary Processes in Hydrogen-Helium Plasmas, Springer-Verlag, Berlin (1987).
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