Evaluation of NRC-FCs1: Mapping the C-field using the Larmor frequency

An uncertainty evaluation of NRC's cesium fountain clock FCs1 is currently being performed. One task of this evaluation consists in quantifying the contribution to the frequency uncertainty, the second-order Zeeman shift. We report the results obtained from measurements of the C-field above the Ramsey cavity using the Larmor frequency as a probe. This technique is possible because a transverse C-field is used in NRC-FCs1 and alignment electrodes are available to produce an orthogonal excitation field. The non-uniformity of the C-field near the Ramsey cavity and the uncertainties in the measurements produce the largest contribution to the type-B uncertainty.