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 × ${10}^{17}$ to 6 × ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$ and temperatures between 40 000 and 45 000 K are achieved in the reflected shock of an electromagnetically driven $⊺$ 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 $\lambda 304$ ÅA, are measured photoelectrically, yielding asymptotic Stark wings (20 ± 20)% below those predicted by Kepple's calculations and showing marked blue shifts of 0.07 ± 0.05 ÅA which may be due to plasma polarization. Photographic wavelength measurements of the first three series members $\lambda 304$, $\lambda 256$, and $\lambda 243$ ÅA are performed relative to the same lines from a Tanaka discharge. Despite some irreproducibilities in the resulting shifts, blue shifts of about 0.04 ÅA at densities near or slightly below 4 × ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$ can be deduced.