Erosion and outgassing behavior of TiN-coated plasma facing components of the Uragan-3M torsatron

Abstract

An erosion behavior of TiN-coated stainless steel (SS) surfaces was investigated during biased-limiter experiments within the Uragan-3M torsatron and during simulation experiments, which were performed with plasma-accelerator and glow-discharge (GD) plasmas. For a TiN-coated SS head-plate of a limiter, the arc ignition probability was found to be lower than 10 −4 per plasma pulse. Possible physical mechanisms of this effect had been discussed. Within special vacuum stands, using thermal-desorption and mass-spectrometry methods, there were performed measurements of an outgassing rate and hydrogen permeability of TiN-coatings. The specific outgassing-rate ( q) of the TiN-coated SS samples, investigated after 3 h baking at 373 K, increased from 5×10 −8 to 5×10 −6 Torr l / s cm 2 when the temperature was increased from 323 to 523 K. The negligible outgassing from TiN-coated SS samples, during their heating up to 473 K, was observed after a cleaning procedure with a molecular hydrogen inflow under a pressure of about 10 −4 Torr, contrary to the considerable increase of ( q) rate for the irradiated samples. Measured values of the TiN-film hydrogen permeability were several times lower, and activation energy of the hydrogen permeation was considerably lower than that for the SS films (15 kJ/mole instead of 19.9 kJ/mole). The use of TiN-coated SS and diffusion membranes for the reduction of erosion, recycling, and hydrogen isotope inventory control, as well as for improvement of vacuum conditions, has been considered.