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

The toroidally-viewing spectroscopic imaging system on Tokamak de Varennes (TdeV) [F. Meo , Rev. Sci. Instrum. 68, (1997)] has given new insight into the physics of a closed divertor, where the particles interact with a verti cally oriented inclined plate situated upstream from the target plate. The system has enabled two-dimensional (2D) measurements of the absolute emissi vities of Hydrogen Balmer lines, as well as Carbon lines. Using the Balmer ratios, the poloidal profile of the electron density has been calculated us ing a Collisional-Radiative model [K. Sawada and T. Fujimoto, J. Appl. Phys . 78, 2913 (1994)]. Results show that the plasma parameters are locally aff ected by the divertor components particularly the inclined plate. This incl ined 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 calc ulated poloidal plasma parameters are projected onto the field lines and ar e used in one-dimensional simplified (1D) particle and momentum balance equ ations. The simplified particle balance equation has shown that the extra n eutrals from the inclined plate increase the parallel velocity locally. Acc ording to the simplified 1D fluid model, the analysis of the momentum balan ce equation has allowed the calculation of the poloidal profile of the ion temperature and hence the ion thermal force. The del T-i force on the impur ity ions increases in the region of the inclined plate, which may seriously affect the impurity retention in the divertor. (C) 2000 American Institute of Physics. [S1070-664X(00)02805-6].