Measurement and interpretation of plasma polarization shift for members of the resonance series of ionized helium

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Abstract
Using an improved T-tube to produce high density helium plasmas, a high density effect connected with the presence of perturbers in the vicinity of a radiating ion has been studied. This effect, the plasma polarization shift, involves the shift of a line under the influence of a perturbing electron. When this electron is considered as bound and forms with the radiating electron a doubly excited state of the ion, the effect corresponds to the emission of dielectronic satellites and is shown to be negligible. When the additional electron is treated as a free perturber the approach of Greig et al. predicts a blue shift as observed here. The red shifts measured for the optically thick lower series members are shown to originate in far wing asymmetries due to higher order effects usually neglected in hydrogenic Stark profiles.