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A novel method for measuring the number density of water molecules in low-temperature plasma is developed. The absolute intensities of rotational lines of the (0,0) band of the OH(A 2Σ–X 2П) transition are used. Lines with sufficiently large rotational quantum numbers referring to the so-called “hot” group of molecules produced by electron-impact dissociative excitation of water molecules are chosen for measurements. The excitation rate of a process with a known cross section is determined by measuring the parameters of plasma electrons by means of the probe method. The measured number densities of molecules are compared with those in the initial plasma-forming mixture. The time evolution of the particle densities in plasma is investigated. The problems of the sensitivity and applicability of the absolute spectral method are considered.

The validation of spectroscopic method for localization of the water plume around a coolant leak in ITER plasma chamber based on the excitation of coolant particles in plasma near wall is presented. The sensitivity of OH hydroxyl and Xe as minor admixtures to cooling water detection in different types of plasma discharges relevant to ITER tested in stellarator L-2M and hollow cathode glow discharge. The limit of sensitivity of water detection in hot plasma using OH* hydroxyl band is estimated as 3 × 10 −5 Pa m 3 s −1 and ∼1 × 10 −6 Pa m 3 s −1 for Xe. For glow discharge conditions measured sensitivity of OH* detection is equal to 3 × 10 −5 Pa m 3 s −1 .

Experimental determination of the sensitivity of the method for detection of water microleakages in the cooling systems of the plasma vacuum chambers of complex electrophysical devices (such as tokamaks, fuel elements of nuclear reactors, and plasmachemical reactors) is considered. It was shown that the spectroscopic method for detection of water microleakages by using the hydroxyl radiation spectrum makes it possible to detect leakages at a level of 10−5 Pa m3 s−1. The spatial resolution of the method allows one to localize defects with an accuracy of several centimeters.

Existing methods of leak detection in vacuum chambers were analyzed from the viewpoint of their application to detect microleaks in the tokamak chamber. Microcrack sizes and leak rates most commonly observed during leak testing of fuel elements are presented. A technique for monitoring microcracking in the tokamak chamber was proposed based on laboratory studies. A series of experiments was performed, which confirmed high sensitivity of the proposed method.

The rectangular hollow cathode discharge is studied with respect to the applicability of similarity mechanisms analogously to other gas discharge types. Probe characteristics of the discharge are measured, the conditions of steady and continuous discharge glow in the cathode cavity are determined.