Measurement of Stark Profiles of the Lyman-αand Lyman-βLines of Hydrogen in an Electromagnetic Shock Tube

Abstract

Measurements in the vacuum ultraviolet spectral region of optically thin (except in narrow wavelength bands in the line cores) profiles of the Stark-broadened Lyman-$\ensuremath{\alpha}$ and Lyman-$\ensuremath{\beta}$ lines of hydrogen (0.03% admixture in 40 mm Hg helium) agreed to within 10% with Stark-broadening theory over three and two decades of intensity, respectively. A shot-to-shot scan technique was employed, using a highly reproducible T-type electromagnetic shock tube. The present theoretical line-broadening calculations include both the effects of quastistatic ion microfields and those of electron impacts, whereas the Holtsmark theory neglects the electrons and differs by a factor of 2-3 on the far wings (depending upon the normalization). A peak temperature of 20 500\ifmmode^\circ\else\textdegree\fi{}K (\ifmmode\pm\else\textpm\fi{}8%) was determined spectroscopically from the helium line-to-continuum intensity ratio and was consistent with the hydrodynamic temperature obtained from shock-velocity measurements. A charged-particle density of a few times ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$, used in comparing the measured profiles with theory, was obtained from the visible continuum intensity and agreed with hydrodynamic predictions, as well as with half-width measurements of neutral helium lines in the visible region.