Shift and width measurements of the Stark-broadened ionized helium line at 1215 Å

Abstract

Time-resolved measurements were made of the shifts of the ionized helium lines at 1640 Å ($n=3\mathrm{}\to 2$) and 1215 Å ($n=4\mathrm{}\to 2$), and of the Stark profile of the $\lambda 1215$-Å line. An electromagnetic shock tube was used as a light source. The plasma conditions corresponded to electron temperatures of ∼3 eV and electron densities of ∼2× ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$. No significant shifts were found for the $\lambda 1640$-Å line. The $\lambda 1215$-Å line underwent a red shift of ≲ 0.5 Å, consistent with semiclassical estimates of plasma polarization shifts. The measured Stark width of the $\lambda 1215$-Å line was 10-45% greater than the calculated width based on the measured width of the $\lambda 4686$-Å line.