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.