Laser spectroscopy for measuring the parameters of a plasma containing helium and argon

Laser spectroscopy diagnostics used in experiments on the PNX-U facility are described. The working gas was argon with an additive of helium. The 2³ P → 3³ D transition was excited by means of optical pumping, and helium fluorescence at wavelengths of 388 and 706.5 nm was observed. The Doppler temperature of helium atoms was determined by scanning the profile of the absorption line with the help of a tunable laser. The sum of the signals so obtained provides information on the local density of helium atoms. It was proposed to determine the local value of the electron density N _e (R) from the ratio between the fluorescence intensities at wavelengths of 388 and 706.5 nm. The ratio of these intensities as a function of N _e for He I was calculated in the collisional-radiative model, and relevant measurements of N _e in the PNX-U facility were performed. When diagnosing the argon component, the main attention was paid to measurements of the ion temperature T _i (R, t). In the course these measurements, anomalous heating of Ar II ions was revealed. The concentration of singly charged argon ions was estimated.