The Effect of Lithium Wall Conditioning in TFTR on Plasma-Surface Interaction

J. Nucl. Mater., 266-269, 1303-1308 (1999).

Ruzic, D. N., Allain, M. C., Budny, R. V.

Five TFTR deuterium supershots with increasing Li pellet injection are analyzed in detail. Five chords of experimental H-α measurements are compared to predictions from a series of computational models. First, experimental data from the discharge is used in the TRANSP plasma transport code to predict the ion flux to the wall. Then a modified version of the DEGAS neutral transport code which includes both reflection, desorption and sputtering of hydrogenic species from the wall is used to determine the neutral density profile across the machine. This data combined with the known density and temperature contours predicts values for the magnitude of H-α light observed for 16 viewing angles of the diagnostic. To match the experimental data, the wall reflection, desorption and sputtering coefficients were altered using data from VFTRIM-3D to include the effect of the added Li. In addition, the first 10 cm of the stainless steel wall adjoining the C inner bumper limiter was treated as C-covered; the highest flux area of the inner wall was treated as a sink; and the lower reflection coefficients for a Li-wall rather than a C-wall were used over an increasingly larger area of the inner wall as the Li concentration in the discharges increased.