Review of the Wall Problem and Conditioning Techniques for Tokamaks

摘要

A variety of conditioning techniques have been applied to tokamaks to control low Z impurities originating from vacuum vessel surface contaminants and to modify the working gas recycling properties. After chemical or physical treatment of the vacuum vessel hardware, in-situ vacuum vessel treatments are usually applied, including: (1) vacuum baking; (2) discharge cleaning; and (3) gettering. As the magnetic fusion program moves to the next generation of large test reactors, the implementation of any of the above techniques becomes a costly procedure. It is therefore prudent to understand the mechanisms and physical-chemical effects of a particular conditioning procedure and maximize the efficiency. A review is given of the present understanding of the physical mechanisms, the resulting surface effects, and benefits to plasma performance of the various conditioning procedures. Particular attention is given to the application of hydrogen glow discharge cleaning and the use of titanium gettering as conditioning procedures. (ERA citation 05:025091)