SPECTROSCOPIC INVESTIGATION OF THE EQUILIBRIUM STATE IN THE ELECTRIC-ARC CATHODE REGION

Several thin layers of an are plasma column were observed side-on at d ifferent distances from the cathode. The are was operated in argon at atmospheric pressure with the are current equal to 200 A. As the basic diagnostic method we used the Olsen-Richter diagrams. For determinati on of temperature the Larenz-Fowler-Milne and Boltzmann plot methods w ere applied. Electron density was measured from the Stark width of the ArII line and continuum intensity. The plasma near the cathode tip sh ows axial and radial dependence of its physical equilibrium state. In the hot core, the plasma is in LTE. Toward outer zones, the plasma sta te deviates from LIE. For plasma layers closer to the cathode, this de viation begins at smaller distances from the axis and for higher tempe ratures it vanishes for h > 3 mm. It is caused after all by the Arl gr ound state overpopulation. Theoretical estimations of the Arl ground s tate overpopulation give results consistent with experiment. Calculati ons show that this overpopulation is caused by inward transport of gro und state atoms into the plasma column.