Speaker
Vladislav Kotov
(Institut für Energie- und Klimaforschung – Plasmaphysik)
Description
First mirrors are plasma facing components which redirect light to the protected optical diagnostics. Initial investigations [A. Litnovsky et al. Nuclear Fusion 49 (2009) 075015, V. Kotov et al. Fusion Eng. Des. 89 (2011) 1583] showed that deposition of impurities (Be, Fe etc.) may cause drastic degradation of the mirror reflectivity and thus severely restrict the diagnostic performance. Very moderate loss of reflectivity was found experimentally under net erosion conditions on the mirror [A. Litnovsky, Fusion Eng. Des. 82 (2007) 123], which would be therefore preferable from the point of view of the diagnostic performance.
It is planned that the diagnostic ducts in the ITER main chamber will be housed in the recessed port plugs which have no direct contact with plasma. Erosion in those areas is expected mainly due to high energetic (charge-exchange) atoms. Local gas puff of deuterium (D2) in front of the port plug can create large fluxes of such atoms and thus enhance re-erosion of deposits. At the same time, erosion from the surfaces in the vicinity of the diagnostic entrance aperture can lead to increased incident fluxes of impurities and increased deposition rate. Hence, accurate numerical calculations are required to estimate the net effect (erosion minus deposition).
In the present paper the transport of neutral particles is modeled with the kinetic Monte-Carlo code EIRENE taking into account 3D geometry of the first wall and ports. The plasma parameters are prescribed based on available experimental data and B2-EIRENE (SOLPS) simulations of the ITER edge plasma. Preliminary studies show that in the vicinity of gas inlet on the port-plug surface the calculated erosion rate of Be is at least a factor of ten larger than its deposition rate. That is, it is highly probable that the gas puff can shift the balance towards net erosion.
Co-author
Vladislav Kotov
(Institut für Energie- und Klimaforschung – Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), Forschungszentrum Jülich GmbH, 52425, Jülich, Germany)
