Stark broadening of the hydrogen Hγ spectral line at moderately low plasma electron densities

The usage of the hydrogen Hγ spectral line for plasma diagnostics, based on Stark broadening at moderately low electron densities (of the order of 1015 cm-3), is experimentally tested and analyzed. As a plasma source, a low-pressure pulsed arc operating in a He-H gas mixture was used. In this electron density range, the Stark broadening of low-order Balmer lines is small, but the broadening of the higher-order members is considerable. Plasma electron densities were deduced from the halfwidth (FWHM) of the measured Hγ profiles in conjunction with the available theoretical results. Further comparison among the electron density values obtained independently using a laser interferometry method and the shape of the He I 4471 A spectral line was also performed. Upon authors knowledge this is the first study of Hγ spectral line undertaken in this way.