Observation of Stark Broadening of Helium in a Turbulent Plasma

Measurements of the $2{}_{}{}^3{}_{}{}^{}P-4\mathrm{}{}_{}{}^3{}_{}{}^{}D$, $4{}_{}{}^3{}_{}{}^{}F$ transitions of neutral helium are carried out in a turbulent linear discharge plasma. The profiles indicate the existence of high-frequency fields generated by plasma instabilities that interact with atoms immersed in the plasma and give rise to quadratic Stark shifts of the allowed line and to second- and fourth-order plasma satellite transitions. A quantitative evaluation of these features indicates the existence of severe inconsistencies in present theoretical calculations.