Abstract
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 language | English (US) |
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Article number | 012003 |
Journal | Journal of Physics: Conference Series |
Volume | 723 |
Issue number | 1 |
DOIs | |
State | Published - Jul 4 2016 |
Event | 8th Symposium on Frequency Standards and Metrology 2015 - Potsdam, Germany Duration: Oct 12 2015 → Oct 16 2015 |
All Science Journal Classification (ASJC) codes
- General Physics and Astronomy