Experimental and theoretical study of the radial distribution of Ar(3P0) metastable atoms in a dc glow discharge in argon

Abstract

Radial distributions of the number density of metastable Ar(3P0) atoms in the positive column of a dc glow discharge in argon were studied both experimentally and theoretically in a wide range of gas pressures (0.1–7 Torr) and discharge currents (10–50 mA). In experiments, glass discharge tubes 4 cm in diameter with clean inner surfaces and surfaces covered with a carbonitride or carbon film were utilized. Measurements were performed using an optical absorption technique known as the method of two identical tubes. Theoretical studies of the discharge plasma parameters under experimental conditions were carried out in the framework of a 1D (along the tube radius) discharge model. By a comparison of radial profiles measured and calculated at a gas pressure of 0.1 Torr the probability of elastic (without quenching) reflection of Ar(3P0) atoms from the tube wall was estimated. For a clean tube wall, this probability is about 0.5 ± 0.3, whereas for a wall covered with a carbonitride or carbon film, it is about zero.