High-density Stark profiles of two neutral helium lines and their forbidden components

Measured and calculated profiles are compared for the two neutral helium lines, He I (λ=4471 and λ=6678 {}) and their forbidden components at electron densities between 1.6 ×{} 10¹⁷ and 4.4 ×{} 10¹⁷ cm^-3. The partially ionized helium plasma was created in the reflected shock of an electromagnetically driven T tube. The electron temperature was measured as {~} 25 000 ^∘{}K. The calculated profiles include a random-phase approximation for the electrons to second-order in the frequency-dependent shift and width operators, and the quasistatic approximation for the ions. Calculations were done at the measured plasma conditions and are compared directly with the experimental profiles. Agreement between theory and experiment is good even though in this density range the line He I (λ=6678 {}) passes from the "isolated-line" to the "overlapping-line" regime, while the line He I (λ=4471 {}) passes from the "overlapping-line" to the "degenerate-hydrogenic" regime.