Plasma parameters of an argon DC arc with graphite electrodes

Plasma temperature and electron density have been measured by optical emission spectroscopy in a transferred direct current arc with graphite electrodes. The measurements were realized for the arc running in a 1.7 cm³ s^-1 argon flow at atmospheric pressure, a current of 200 A, a voltage of 48±2 V and with a distance of 85 mm between the electrodes. Specially designed electrodes were developed to minimize displacements of the arc because of movements of the electrode spots. In this way, the measurement errors have been greatly diminished. The measurements were made supposing an optically thin collisionally dominated plasma of axial symmetry. Density distributions of excited argon atoms and ions on their energy levels were determined to evaluate plasma temperature. The half-widths of spectral lines were used to reach the electron density in the plasma. Spatial distributions of the measured parameters are presented for the arc positive column and near the electrodes. Maximum values of 1.5 × 10¹⁷ cm^-3 and 13 500 K were found close to the cathode for the electron density and temperature, respectively. The data and possible reasons for some of the variation found in the observed results are discussed.