Detection of water molecules in inert gas based plasma by the ratios of atomic spectral lines

Abstract

A new approach is considered to detect the water leaks in inert plasma-forming gas present in the reactor chamber. It is made up of the intensity ratio of Dα and Hα spectral lines in combination with O, Ar and Xe lines intensity. The concentrations of H2O, O, H and D particles have been measured with high sensitivity. At the D2 admixture pressure = 0.025 mbar, we used the acquisition time of 10 s to measure the rate of water molecules injected from the outside, Γ0 = 1.4 · 10−9 mbar · m3 · s−1, and the incoming water molecules to plasma, Γ = 5 ·10−11 mbar · m3 · s−1. The scaling proves that at small D2 admixtures (10−4 mbar), the leaks with the rates Γ0 ≈ 6 · 10−12 mbar · m3 · s−1 and Γ ≈ 2 · 10−13 mbar · m3 · s−1 can be detected and measured. The difference between Γ0 and Γ values is due to the high degree of H2O dissociation, which can be up to 97–98%.