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The chemical composition of the discharge plasma in inert gases with H2O and D2 additives is investigated experimentally and theoretically for the first time. A new approach is applied to the measurement of the concentrations of plasma-produced particles. It includes the combination of the optical multispectral actinometry technique and the concept of intermediate chemically active actinometers. The scheme of the chemical processes in the plasma is elaborated. The dynamics and steady state concentrations of near 20 atomic and molecular particles are described. The experimental data on particle densities are in good agreement with the calculated values. The data on stationary particle concentrations with a variation of H2O (106–1016) cm−3 and D2 (1012–1016) cm−3 are presented. Within these limits, the concentrations of chemically active atoms as well as 2-, 3-, and 4-atomic molecules are in the (103–9.6 × 1015) cm−3 interval. The use of the new improved technique of actinometry combined with the modeling code significantly extends the capabilities of the highly sensitive spectral emission technique for the analysis of the chemical composition of the multi-component plasma.

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 D α and H α spectral lines in combination with O, Ar and Xe lines intensity. The concentrations of H 2 O, O, H and D particles have been measured with high sensitivity. At the D 2 admixture pressure p D2 = 0.025 mbar, we used the acquisition time of 10 s to measure the rate of water molecules injected from the outside, Γ 0 = 1.4 • 10 −9 mbar • m 3 • s −1 , and the incoming water molecules to plasma, Γ = 5 •10 −11 mbar • m 3 • s −1 . The scaling proves that at small D 2 admixtures (10 −4 mbar), the leaks with the rates Γ 0 ≈ 6 • 10 −12 mbar • m 3 • s −1 and Γ ≈ 2 • 10 −13 mbar • m 3 • s −1 can be detected and measured. The difference between Γ 0 and Γ values is due to the high degree of H 2 O dissociation, which can be up to 97-98%.

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