Improved accuracy of the NPLCsF2 primary frequency standard: evaluation of distributed cavity phase and microwave lensing frequency shifts
Abstract
We evaluate the distributed cavity phase (DCP) and microwave lensing frequency shifts, which were the two largest sources of uncertainty for the NPLCsF2 caesium fountain clock. We report measurements that confirm a detailed theoretical model of the microwave cavity fields and the frequency shifts of the clock that they produce. The model and measurements significantly reduce the DCP uncertainty to 1.1 × 10^{16}. We derive the microwave lensing frequency shift for a cylindrical cavity with circular apertures. An analytic result with reasonable approximations is given, in addition to a full calculation that indicates a shift of 6.2 × 10^{17}. The measurements and theoretical models we report, along with improved evaluations of collisional and microwave leakage induced frequency shifts, reduce the frequency uncertainty of the NPLCsF2 standard to 2.3 × 10^{16}, nearly a factor of two lower than its most recent complete evaluation.
 Publication:

Metrologia
 Pub Date:
 October 2011
 DOI:
 10.1088/00261394/48/5/007
 arXiv:
 arXiv:1107.2412
 Bibcode:
 2011Metro..48..283L
 Keywords:

 Quantum Physics;
 Physics  Atomic Physics
 EPrint:
 Metrologia 48, 283289 (2011)