Determining the charged particle concentration in a dc arc from the emission spectrum of sodium

Several methods of measuring charged particle concentrations from the emission spectrum of sodium are discussed. The limits of applicability of each method are specified. Discrepancies in charged particle concentrations measured on the basis of the broadening of spectral lines with different Stark constants in an arc discharge are due to the fact that the peak intensities of these lines are determined in various narrow discharge zones. A method for determining the charged particle concentration over the radius of an inhomogeneous axisymmetrical source (arc discharge) from the broadening of several emission lines of sodium with different Stark constants is proposed. It is shown that in the case of strongly inhomogeneous sources the vanishing of spectral lines from the series cannot be used to determine the charged particle concentration in the plasma.In conclusion, the authors wish to thank M. A. El'yashevich for discussing the present paper.