Highly Charged Ion Sources for Precision Measurements

Several species of highly charged ions (HCIs) with ionization energies below 1 keV have been proposed for use in the development of next-generation optical clocks, searches for possible time-variation of the fine structure constant (dα/dt * 1/α), and in spectroscopic tests of quantum electrodynamics (QED). For example, Pr¹⁰⁺ and Ba⁴⁺ have been identified as promising candidates for the development of high-accuracy optical clocks with a high sensitivity to (dα/dt * 1/α) and favorable systematics, compared to current neutral atom and singly charged ion-based optical clocks^1,2. Traditionally, HCIs have been produced and studied in large-scale facilities equipped with electron beam ion sources/traps (EBIS/T) that rely on superconducting Helmholtz magnet coils. However, the advent of high-field permanent magnets, like those based on neodymium iron boron (NdFeB) and samarium cobalt (SmCo), has enabled the development of smaller HCI sources for tabletop experiments. A major benefit of permanent-magnet HCI sources is their ability to easily integrate ablation targets for metal HCI production. Here, we present recent work on the development of a compact electron beam ion trap with a 0.25 T trapping magnetic field to support this entire range of proposed HCIs. Additionally, a smaller ion source, optimized for the production of Ba⁴⁺ is currently being developed. We present the relevant physics of electron beam ion sources and traps, along with the processes of extracting, identifying, selecting, pre-cooling, and loading ions into a radiofrequency (rf) Paul trap for laser spectroscopy and clock operation applications.

[1] S. G. Porsev, et al., Phys. Rev. A 110, 042823 (2024).

[2] S. O. Allehabi, et al., Phys. Rev. A 106, 043101 (2022).