Buffer gas consumption in rubidium discharge lamps

We present a physics-based empirical model of a newly discovered potential failure mode of rubidium atomic clocks: exhaustion of the noble gas buffer in the rubidium discharge lamp. We attribute the buffer gas loss to noble gas ion capture (NIC) by the glass walls of the lamp. The noble gas ions are produced by multistep ionization in collisions with discharge electrons. The model explains the observed pressure dependence of the buffer gas loss rate, and predicts an extremely high sensitivity of the loss rate to discharge electron temperature. That prediction is confirmed by comparison with experimental data. The model needs further work to be fully validated. We propose that longest lamp life can be achieved by minimizing noble gas light emission while keeping Rb light emission at the level required to achieve the desired atomic clock performance.