EXPERIMENTAL MEASUREMENTS OF THE FUELING EFFICIENCY OF IMPURITIES INJECTED INTO TEXTOR

Impurity fuelling has been studied in TEXTOR by gas puffing under a wi de range of experimental conditions. First, neon has been injected int o discharges with a range of densities during both Ohmic and neutral i njection heating. Then, helium, neon and argon have been injected into similar discharges and the increase in radiated power and Z(eff) stud ied as a function of the number of impurity atoms injected. Similar ex periments using carbon monoxide and methane yielded markedly different results from those of the rare gases. The fraction of injected atoms entering the confined plasma has been estimated and found to vary wide ly, from less than 1 % for carbon to about 100 % for helium. Detailed Monte Carlo calculations performed using the LIM code to simulate the impurity behaviour have shown that good agreement with experiment can be obtained for all species except oxygen, where charge exchange proce sses are thought to be important.