Stark broadening of the hydrogen resonance lineLβin a dense equilibrium plasma

Profiles of $L_{\beta }$ emitted from small hydrogen additions in a dense argon plasma ($n_e=1, 2, \mathrm{and} 3\times {10}^{23}$ ${\mathrm{m}}^{-3\mathrm{}}$, $T\approx {10}^4$ K) were measured under controlled optical depth over wavelength separation $\Delta \lambda$ from ${\lambda }_{L\beta }$ of about eight times the half-halfwidth $\Delta {\lambda }_{\frac{1}{2}}$. Reabsorption in the boundary layers of the plasma, usually caused by hydrogen as well as argon atoms, was avoided. The Stark profiles $P\left(\Delta \lambda \right)$ obtained (uncertainty ±4% for $\frac{\left|\Delta \lambda \right|}{\Delta {\lambda }_{\frac{1}{2}}}\le 4$) were found to be for $\frac{\left|\Delta \lambda \right|}{\Delta {\lambda }_{\frac{1}{2}}}>0.6\mathrm{}$ in good agreement with calculations according to the "unified" theories (Vidal et al. and Seidel) and to the modified impact theories (Griem and Bacon). For $\frac{\left|\Delta \lambda \right|}{\Delta {\lambda }_{\frac{1}{2}}}<0.6\mathrm{}$ deviations remain, particularly in the line center, even when time ordering and ion dynamics (Seidel) are taken into account. These residual discrepancies indicate, in accordance with deviations recently found for $L_{\alpha }$, that broadening mechanisms which are not finally identified are efficacious. The experimental $L_{\beta }$ profiles exhibit an asymmetry behavior similar to that calculated by Bacon, yielding that the asymmetry is mainly caused by ion-field inhomogeneities. Using the scale of angular frequencies the change of sign of the asymmetry is found to be at $\frac{\Delta \omega }{\Delta {\omega }_{\frac{1}{2}}}=0.5\mathrm{}$, whereas it is predicted by Bacon at $\frac{\Delta \omega }{\Delta {\omega }_{\frac{1}{2}}}=1.2\mathrm{}$. The measurements indicate red shifts of the centers of the profiles of about ${10}^{-2\mathrm{}}\Delta {\omega }_{\frac{1}{2}}$ (≃ ${10}^{-3\mathrm{}}$ nm for $n_e=2\mathrm{}\times {10}^{23}$ ${\mathrm{m}}^{-3\mathrm{}}$).