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

Time-resolved measurements were made of the shifts of the ionized helium lines at 1640 A (n = 3 → 2) and 1215 A (n = 4 → 2), and of the Stark profile of the lambda1215-A line. An electromagnetic shock tube was used as a light source. The plasma conditions corresponded to electron temperatures of approx. 3 eV and electron densities of approx. 2 x 1017 cm-3. No significant shifts were found for the lambda1640-A line. The lambda1215-A line underwent a red shift of approximately-less-than 0.5 A, consistent with semiclassical estimates of plasma polarization shifts. The measured Stark width of the lambda1215-A line was 10--45% greater than the calculated width based on the measured width of the lambda4686-A line