  Accurate spectroscopy of highly charged high-Z ions in a storage ring is
demonstrated to be feasible by the use of specially adapted crystal optics. The
method has been applied for the measurement of the 1s Lamb shift in
hydrogen-like gold (Au 78+) in a storage ring through spectroscopy of the Lyman
x rays. This measurement represents the first result obtained for a high-Z
element using high-resolution wavelength-dispersive spectroscopy in the hard
x-ray regime, paving the way for sensitivity to higher-order QED effects.
