Characterization of minority species in reactive plasmas by cryotrap-assisted mass spectrometry

Abstract

In this work, the characterization of minority species produced in reactive plasmas by the cryotrap-assisted mass spectrometry technique (CTAMS) is addressed. A H2/CH4/N2 mixture (90 : 5 : 5) was fed into a dc glow discharge and analysed by conventional and CTAMS. The gaseous mixture was chosen because of its particular relevance in the inhibition of tritium-rich carbon film deposition in fusion plasmas (scavenger technique). Condensation of some reactive intermediates in the liquid nitrogen trap was achieved. Strong changes in the composition of such species upon changes in the reactor walls or in the way they are sampled (length of the metallic duct) were detected. They are analysed in terms of radical formation and recombination in the reactor system, thus providing some insight into the underlying mechanism responsible for the film inhibition in nitrogen/carbon containing plasmas, a well-known effect in the plasma deposition of a-C : N (H) films.