Spectroscopic measurements of electron density of capillary plasma based on Stark broadening of hydrogen lines

A set of measurements of the electron density of plasma jets, generated by a high-pressure discharge capillary operating at quasi-steady-state, is described. The method of measurement is based on the dependence of Stark broadening of the hydrogen ${\mathrm{H}}_{\mathrm{\alpha }}$ and ${\mathrm{H}}_{\mathrm{\beta }}$ spectral lines on the electron density. Spectra were sampled electronically, time integrated over the electrical pulse duration, for various capillary currents and at different axial locations along the emerging plasma jet. The comparison of model predictions [Loeb and Kaplan, IEEE Trans. Magn. 25, 342 (1989)] with electron densities deduced from these spectra, by applying the theory of Stark broadening [Griem, Spectral Line Broadening by Plasma (Academic, New York, 1974)], indicates a good agreement over the tested current (1–8 kA) and density (${10}^{17}$–${10}^{19}$ ${\mathrm{cm}}^{\mathrm{-}3}$) ranges. At larger densities, self-absorption might be a problem.