Impurity characteristics of TMX-U

A study of the concentrations, radiated power, and sources of impurities in the TMX-U plasma is presented. Three extreme ultraviolet (EUV) instruments were used: one monochromator that measures time-resolved radial profiles of a particular impurity line, and two time-resolving spectrographs that measure the time histories of several impurity lines in a single shot. The major impurities found in the TMX-U plasma are carbon, nitrogen, and oxygen. Titanium and silicon are also observed. The impurity concentrations are low, less than 1% and the radiated power is a small fraction of the input power. The major source of oxygen and nitrogen is the neutral beam injector. Wall conditioning, such as glow discharge cleaning and titanium gettering, decreases the impurity concentrations, particularly carbon. There does not seem to be an accumulation of impurities in the thermal barrier region under the present plasma conditions. Future experiments are discussed.