NPL Cs fountain frequency standards and the quest for the ultimate accuracy

K. Szymaniec, S. N. Lea, K. Gibble, S. E. Park, K. Liu, P. Głowacki

Research output: Contribution to journalConference articlepeer-review

23 Scopus citations


NPL operates a system of two primary caesium fountain clocks consisting of a fully characterised standard NPL-CsF2 together with a new standard NPL-CsF3, which has recently become operational. Both fountains feature a single-stage vapour-loaded magneto-optical trap as the source of cold atoms and an approximate cancellation of the potentially large cold collision frequency shift. As a result, the collision-shift type-B uncertainty is less than 10-16. Subsequently, more subtle systematic effects, including the frequency shifts from distributed cavity phase, microwave lensing and collisions with background gas have also been evaluated at the level of 10-16 or below. Now, as several systematic effects contribute to the fountains' uncertainty budgets similarly, further significant improvement of their accuracies is expected to be even more difficult. The short-term stability of these standards is also a significant factor limiting the overall precision as many days or even weeks of averaging is required for the type-A statistical uncertainty to approach the declared type-B systematic uncertainty. Going forward, further improvements in the reliability and robustness of operation of fountain standards is one of our priorities.

Original languageEnglish (US)
Article number012003
JournalJournal of Physics: Conference Series
Issue number1
StatePublished - Jul 4 2016
Event8th Symposium on Frequency Standards and Metrology 2015 - Potsdam, Germany
Duration: Oct 12 2015Oct 16 2015

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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