Initial wall conditioning for the TMX‐U fusion experiment

The introduction of impurities and hydrogen from the walls and liners of the TMX‐U device can have a deleterious effect on the plasma. The area of these surfaces is large (∼107 cm2) and has a complicated shape, so cleaning is difficult. Techniques that have been used to condition these walls include (1) initial solvent cleaning; (2) baking; (3) glow discharge cleaning; (4) gettering; and (5) plasma clean up. Several diagnostic techniques, including UV and visible spectroscopy and residual gas analysis, have been used to evaluate the effectiveness of the conditioning procedures. A series of experiments was performed to optimize the glow discharge in the TMX‐U geometry; during approximately 80 h of glow discharge cleaning, low‐Z impurities were removed. Gettering along with pumping with liquid‐nitrogen‐cooled liners and cryopumps resulted in base pressures ∼10−8 Torr. This paper describes these procedures and their importance in the formation of initial plasmas in TMX‐U.