CARBON AND OXYGEN BEHAVIOR IN THE REVERSED-FIELD PINCH RFX

The emission spectrum measured on the reversed field pinch RFX is domi nated by carbon and oxygen lines. Nickel lines are seldom observed eve n though a large magnetic field perturbation causes intense plasma-wal l interaction. The line emissions from hydrogen-like and helium-like i ons observed in RFX are simulated by a collisional-radiative impurity diffusion model. An impurity diffusion coefficient of the order of 10 m(2)/s and an inward convective velocity of 90 m/s have been used for an adequate simulation of the hydrogen-like to helium-like resonant li ne ratios. The model can be used to estimate the effective charge of t he plasma; the on-axis values in 800 kA discharges are found to range between 1.5 and 2.2, with peaks higher than 3 in the presence of carbo n blooms. It is found that charge exchange processes with thermal hydr ogen neutral atoms must be considered to account for the high G ratio values measured for carbon (0.6 to 0.7).