Influence of ion dynamics on the width and shift of isolated He i lines in plasmas

Abstract

We report measured Stark widths and shifts of the neutral helium lines 3889 and 5876 A\r{} in hydrogen-helium, pure helium, and argon-helium plasmas. A pulsed low-pressure arc is used as a plasma source. Electron densities of (2--10)\ifmmode\times\else\texttimes\fi{}${10}^{16}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ are measured by laser interferometry, electron temperatures in the range from 31 000 to 42 000 K are determined from the intensity ratio of O ii impurity lines, and the gas temperature is determined from the Doppler component of the O ii line profile. Experimental Stark widths and shifts are compared with theoretical results obtained from three sets of semiclassical calculations of Stark-broadening parameters using quasistatic and ion-dynamic treatment of the ions. Inclusion of ion dynamics in the calculation of widths and shifts considerably improves the agreement between theory and experiments. The results of the comparison show a constant systematic discrepancy between three semiclassical calculations and the experiment. These results suggest the possibility of plasma-electron-density diagnostics with a precision in the range 3--5 %.