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Density Measurements from the Asymmetry of the Lyman ζ Line in a Vacuum Spark Lithium Discharge

A lithium spectrum is obtained form vacuum spark discharges using a grazing‐incidence flat‐field spectrometer. Hydrogen‐like lines up to Lyman η are identified in the spectrum. The spectrum is analyzed, and it is found that the experimental line widths increase along the Lyman series. An asymmetry between the blue and red wings appears in the profile of the Lyman ζ line, and becomes significant in the profile of the Lyman ϵ line. A relatively new method is used to estimate an electron density of 1 ± 0.4 × 1018cm−3 from the experimental degree of asymmetry between the blue and the red wings of the Lyman ζ line. This result is compared with an analysis of the experimental widths of two optically thin lines, namely, Lyman δ and Lyman ζ. In this analysis an electron density of 1.2±0.5 × 1018cm−3 is deduced. The principal quantum number of Lyman η (n=8) is used in the Inglis‐Teller formula for the last line seen before the merging of the lines with the continuum, and the estimated electron density is found to be 2.0 × 1018cm−3 for the lithium plasma. Thus, it is demonstrated that the new method employing the asymmetry of the lineshapes in dense plasmas yields results consistent with the analysis of the widths of the lines. However, it requires obtaining the profile of just one spectral line, which is a great advantage. The reference data on the Stark broadening of the Lyman ζ line is also tabulated, which was previously unavailable in the literature.