Local effects of upstream divertor components on divertor plasma parameters and impurity retention forces

Abstract

The toroidally-viewing spectroscopic imaging system on Tokamak de Varennes (TdeV) [F. Meo et al., Rev. Sci. Instrum. 68, (1997)] has given new insight into the physics of a closed divertor, where the particles interact with a vertically oriented inclined plate situated upstream from the target plate. The system has enabled two-dimensional (2D) measurements of the absolute emissivities of Hydrogen Balmer lines, as well as Carbon lines. Using the Balmer ratios, the poloidal profile of the electron density has been calculated using a Collisional-Radiative model [K. Sawada and T. Fujimoto, J. Appl. Phys. 78, 2913 (1994)]. Results show that the plasma parameters are locally affected by the divertor components particularly the inclined plate. This inclined plate constitutes an extra recycling surface which causes an increase in the atomic density and a decrease in the electron density in this region and affecting the plasma parameters at the target plate. Finally, the calculated poloidal plasma parameters are projected onto the field lines and are used in one-dimensional simplified (1D) particle and momentum balance equations. The simplified particle balance equation has shown that the extra neutrals from the inclined plate increase the parallel velocity locally. According to the simplified 1D fluid model, the analysis of the momentum balance equation has allowed the calculation of the poloidal profile of the ion temperature and hence the ion thermal force. The ∇Ti force on the impurity ions increases in the region of the inclined plate, which may seriously affect the impurity retention in the divertor.