Proposed precision laser spectrometer for trapped, highly charged ions
  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. 
M. Vogel, D.F.A. Winters, D.M. Segal and R.C. Thompson