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

Time-resolved measurements were made of the shifts of the ionized helium lines at 1640 {} (n=3→2) and 1215 {} (n=4→2), and of the Stark profile of the λ1215-{} 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×{} 10¹⁷ cm^-3. No significant shifts were found for the λ1640-{} line. The λ1215-{} line underwent a red shift of {} 0.5 {}, consistent with semiclassical estimates of plasma polarization shifts. The measured Stark width of the λ1215-{} line was 10-45% greater than the calculated width based on the measured width of the λ4686-{} line.