  We propose a novel type of precision laser spectrometer for trapped, highly
charged ions nearly at rest. It consists of a cylindrical open-endcap Penning
trap in which an externally produced bunch of highly charged ions can be
confined and investigated by means of laser spectroscopy. The combination of
confinement, cooling and compression of a dense ion cloud will allow the ground
state hyperfine splitting in highly charged ions to be measured with an
accuracy three orders of magnitude better than in any previous experiment. A
systematic study of different charge states and different isotopes of the same
element allows for highly sensitive tests of bound-state QED and for a
precision determination of nuclear properties. Apart from stable isotopes, also
radioactive species with half-lives longer than about one hour can be
investigated.
