High-precision mass spectrometer for light ions

The precise knowledge of the atomic masses of light atomic nuclei, e.g., the proton, deuteron, triton, and helion, is of great importance for several fundamental tests in physics. However, the latest high-precision measurements of these masses carried out at different mass spectrometers indicate an inconsistency of five standard deviations. To determine the masses of the lightest ions with a relative precision of a few parts per trillion and investigate this mass problem, a cryogenic multi-Penning-trap setup, LIONTRAP (Light-Ion Trap), was constructed. This allows an independent and more precise determination of the relevant atomic masses by measuring the cyclotron frequency of single trapped ions in comparison to that of a single carbon ion. In this paper the measurement concept and a doubly compensated cylindrical electrode Penning trap are presented. Moreover, the analysis of the first measurement campaigns of the proton's and oxygen's atomic mass is described in detail, resulting in m(p) = 1.007 276 466 598 (33) u and m(O-16) = 15.994 914 619 37 (87) u. The results on these data sets have already been presented by F. Heisse et al. [Phys. Rev. Lett. 119, 033001 (2017)]. For the proton's atomic mass, the uncertainty was improved by a factor of three compared to the 2014 CODATA value.