TY - JOUR
T1 - NPL Cs fountain frequency standards and the quest for the ultimate accuracy
AU - Szymaniec, K.
AU - Lea, S. N.
AU - Gibble, K.
AU - Park, S. E.
AU - Liu, K.
AU - Głowacki, P.
PY - 2016/7/4
Y1 - 2016/7/4
N2 - 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.
AB - 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.
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U2 - 10.1088/1742-6596/723/1/012003
DO - 10.1088/1742-6596/723/1/012003
M3 - Conference article
AN - SCOPUS:84979256978
SN - 1742-6588
VL - 723
JO - Journal of Physics: Conference Series
JF - Journal of Physics: Conference Series
IS - 1
M1 - 012003
T2 - 8th Symposium on Frequency Standards and Metrology 2015
Y2 - 12 October 2015 through 16 October 2015
ER -