Visible light spectroscopy of TRIAM-1M plasma

Numerical simulation of impurities transport and visible light spectroscopy are carried out to investigate the behaviors of impurities in TRIAM-1M superconducting tokamak plasma. Major impurities are low-Z substances, including carbon and oxygen. The density of carbon and oxygen impurities at an early stage of discharge (0.5 ms) is about 1.06 x 1011 cm-3 and 2.00 x 1011 cm-3, respectively. After a mid stage (50 ms), the time dependence of radiation intensity, especially that of OII (4419.9 A), on carbon and oxygen impurities is largely affected by the displacement of plasma. Simulation of the wave profiles of OII and OIV (3071.7 A) shows that observed wave profiles can be interpreted qualitatively by models that takes into account the steady inflow of impurities, the unusual transport toward the center of the plasma due to unusual diffusion or convection, etc. These models serve to determine the density distribution of impurity ions at 50 ms. The damping radiation loss at 50 ms is about 0.01 ∼ 0.02 % of the linear radiation loss. The total radiation loss is rather low, 16.5 % of the ohmic input. The effective charge at this stage is also low; maximum 1.4 and average 1.15. A change in OII radiation intensity seen at a mid stage of plasma discharge can be attributed to an increase in the inflow of oxygen impurity due to a displacement of the plasma. These phenomena are accompanied by an increase in radiation loss in the periphery of the plasma. The phenomena may be prevented by minimizing the displacement of the plasma. (Nogami, K.)