Stark broadening of visible neutral helium lines in a plasma

Physics

Scientific paper

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Helium Plasma, Plasma Jets, Plasma Spectra, Spectral Line Width, Stark Effect, Visible Spectrum, Atomic Energy Levels, Electron Density (Concentration), Electron Energy, Fine Structure, Gas Temperature, Ion Motion, Line Spectra, Monochromators, Optical Thickness, Plasma Diagnostics

Scientific paper

Side-on observations of the visible spectrum emitted by a helium plasma generated in a wall-stabilized arc are reported. Electron densities range from 0.2 to 1.3 x 10 to the 22nd/cu cm and electron temperatures vary from 10,000 to 20,000 K. Most of the 17 measured lines are isolated at the conditions of the experiment. Electron densities derived from the Stark-widths of the isolated lines agree to within 15% of the values determined from H beta and from the quasi-degenerate HeI lines at 4471 and 4921 A. Similar agreement is observed for the static-ion Stark broadening parameters. However, at the conditions of this experiment, the static-ion approximation is not valid near the center of some of the isolated lines. The observation of ion-dynamic effects in neutral isolated lines is reported here for the first time. In the isolated lines, the measured ion-dynamic effects are reasonably consistent with calculations based on an adiabatic unified theory for the ion perturbers. A simple parametric expression closely approximates the ion-dynamic contribution to the half-width of isolated lines. Hydrogenic (nonisolated) neutral helium lines exhibit a large discrepancy with theoretical profiles near the line center, where ion-dynamic effects are important.

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