Spectroscopic study of sources and control of impurities in TMX-U

An absolutely calibrated spectrograph has been used to study the impurity characteristics in the Tandem Mirror Experiment-Upgrade (TMX-U). The spectrograph measures the time histories of several impurity emission lines in a single plasma shot. The common intrinsic impurities found in TMX-U are C, N, O, and Ti. It has been shown that a large fraction of oxygen and nitrogen in the plasma is associated with the neutral beams. The plasma wall is the main source of carbon. In general, the concentration of each of the impurities is low (<1%), and the power radiated by them is less than 10 kW, which is a small portion of the total input power to the plasma. The concentrations of the impurities can be reduced substantially by glow discharge cleaning and titanium gettering