Studies of fuelling rates of CO, CH4 and oxygen in the TEXTOR tokamak

Impurity gases have been introduced into TEXTOR at well defined rates to study the fuelling process and the effect they have on the overall energy balance. It is found that carbon and oxygen, introduced as CO and CH 4 gases have radically different behaviour. Oxygen has a high recycling coefficient ∼-0.99 whereas carbon has a low recycling coefficient ∼-0.3. The radial position of the gas source was varied from the wall to the limiter radius but this made little difference to the effect on the global plasma parameters. For very high impurity influxes of both impurities drastic changes in the edge plasma were observed and disruptions could be induced.