Precision measurement of the 1<i>s</i>Lamb shift in hydrogenlike argon

Precision measurements of the absolute wavelengths of the Lyman-\ensuremath{\alpha} doublet (2p ${\mathrm{}}^{2}$${P}_{3/2}$,1/2 \ensuremath{\rightarrow}1s ${\mathrm{}}^{2}$${S}_{1/2}$) in hydrogenlike argon (${\mathrm{Ar}}^{17+}$), as well as those of some strong dielectronic satellites, are reported. The Alcator C tokamak plasma was seeded with trace amounts of argon and the emission spectra were taken with a high-resolution, crystal x-ray spectrometer. In situ wavelength calibration was achieved by utilizing the potassium K\ensuremath{\alpha} lines from a KCl fluorescence source. For the Ly${\ensuremath{\alpha}}_{2}$ line, a precision of 11 ppm was achieved. Comparisons of these data with QED predicted wavelengths show good agreement, yielding a test of the 1s Lamb shift at the 3% level. The precision of these measurements was limited by uncertainties in the wavelength calibration, with the uncertainties due to the influence of unresolved satellites being of secondary importance.