Experimental investigation of Stark broadening and plasma polarization shift of ionized helium resonance lines

Abstract

Stark broadening and shift measurements of ionized helium resonance lines from a fully ionized helium plasma are reported. Electron densities in the range from 2 \ifmmode\times\else\texttimes\fi{} ${10}^{17}$ to 6 \ifmmode\times\else\texttimes\fi{} ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and temperatures between 40 000 and 45 000 K are achieved in the reflected shock of an electromagnetically driven $\ensuremath{\intercal}$ tube. All observed Hell resonance lines are emitted optically thick by a nearly homogeneous plasma slab and self-reversed by a very thin, cooler boundary layer. Profiles of the first resonance line, Hell $\ensuremath{\lambda}304$ \AA{}A, are measured photoelectrically, yielding asymptotic Stark wings (20 \ifmmode\pm\else\textpm\fi{} 20)% below those predicted by Kepple's calculations and showing marked blue shifts of 0.07 \ifmmode\pm\else\textpm\fi{} 0.05 \AA{}A which may be due to plasma polarization. Photographic wavelength measurements of the first three series members $\ensuremath{\lambda}304$, $\ensuremath{\lambda}256$, and $\ensuremath{\lambda}243$ \AA{}A are performed relative to the same lines from a Tanaka discharge. Despite some irreproducibilities in the resulting shifts, blue shifts of about 0.04 \AA{}A at densities near or slightly below 4 \ifmmode\times\else\texttimes\fi{} ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ can be deduced.