Experiment at NIST to produce one-electron ions in circular Rydberg states

Highly charged ions, including bare nuclei, produced in the NIST EBIT (electron beam ion trap) are extracted and captured in the simplest Penning trap that can be configured with a single neodymium (NdFeB) magnet.\footnote{N. Guise, S.M. Brewer and J.N. Tan, oral presentation at this meeting} Slowing and capture of bare nuclei is a step towards formation and study of one-electron ions within the well-controlled environment of a Penning or Paul trap. Detailed laser spectroscopy of hydrogen- like ions in circular Rydberg states would potentially provide a test of theory in a regime with completely negligible nuclear- size corrections.\footnote{U.D. Jentschura, \textit{et al.}, Phys. Rev. Lett. \textbf{100}, 160404 (2008).} Such a test is of particular interest in the wake of the large discrepancy in proton radius determinations that resulted from the muonic hydrogen Lamb-shift measurements.\footnote{R. Pohl, \textit{et al.}, Nature \textbf{466}, 213-218 (2010).} We discuss some experiments with captured ions planned in a more elaborate apparatus configured with a two-neomagnet (NdFeB) Penning trap for better magnetic field homogeneity, an electron gun for in- trap loading of low-$Z$ ions, and optical access for spectroscopy experiments with low-energy, highly-charged ions.