Plasma processes primary limitations

At present, reproducibility and control are the primary limitations to the implementation of plasma processes clearly, the large number of interacting parameters accounts for such problems. In addition, deposition and etching processes are inordinately sensitive to small (part-per-billion) concentrations of impurities. These difficulties can be overcome only by careful investigation of the complex chemistry and physics of glow discharges. 

The initial contamination of a Tokamak plasma used to be dominated by oxygen and carbon which are released from the wall and from the limiter due to desorption (see Sect. 5.5.). These impurities were of primary concern in most machines until the discharge cleaning technique came to be routinely used54). In addition to the various desorption processes, a number of other impurity release mechanisms need to be considered. Among these are ... 

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