An ion-based atomic clock includes an ion trap, a cooling laser, a re-pumping source and a frequency comb source. The ion trap can trap a plurality of Ra+ ions generated by an ion generator. The cooling laser can facilitate trapping of the plurality of Ra+ ions within the ion trap and populate excited state levels in the trapped Ra+ ions. The re-pumping source can trigger decaying of the excited state levels to a first metastable level. The frequency comb source can directly drive a multi-terahertz (multi-THz) clock transition between the first metastable level and a second metastable level in the trapped Ra+ ions. A signal derived from the population remaining in the first metastable level following the driving of the clock transition can be used to guide the repetition rate of the frequency comb source to an accurate frequency related to the clock transition frequency.