Characterization of low-pressure high-current cascaded arc plasma in large volumes

Abstract

A comprehensive study of behavior and parameters of the low-pressure (1–20 mTorr) large-area plane–symmetric direct current arc discharge plasma in pure Ar and Ar-N2 mixtures was carried out. A low-pressure arc discharge was ignited in a large chamber between a planar vacuum arc cathode with magnetic steering of arc spots and a surrounding grounded primary anode while a long-length remote arc discharge was extended toward a remote linear anode parallel to the cathode plate. The arc column moved up and down along the cylindrical cathode target positioned perpendicular to the cathode-to-remote anode direction, following the motion of the cathodic arc spots. Current-voltage characteristics of the low-pressure direct current arc discharge, electron density, electron temperature, electron energy distribution function (EEDF), ion energy distribution function (IEDF) and dissociation of nitrogen molecules in the discharge were studied using electro-technical methods, electrostatic probes, a microwave resonant probe, an ion energy analyzer and optical emission spectroscopy (OES) methods. A number of OES methods were used to determine temperature and density of electrons in the discharge: the Te was measured using 1) the IArI,415/IArI,306 intensity ratio, 2) an intensity ratio of the (0–0) vibrational bands of 1st negative and 2nd positive systems of N2; the ne was obtained by 1) the IArII,487/IArI,451 intensity ratio and 2) ratio of N2(C3Πu,v = 1) and N2(C3Πu,v = 0) populations. In addition, the nitrogen dissociation degree was monitored using INI,868.03/IArI,852.14 and INI,862.92/IArI,852.14 intensity ratios. Spectral and probe measurements of Te and ne in the large-area arc discharge show reasonable agreement. The electron population analysis based on the second derivative of the Langmuir probe current-voltage characteristics allowed accurate measurements of electron population parameters in the discharge including EEDF, electron drift velocity along with plasma potential, electron density and energy. Modeling of the low-pressure large-volume arc discharge using the axially symmetric drift-diffusion approximation exhibited good qualitative and acceptable quantitative agreement between calculated plasma parameters and experimental data.