Initial Study of the Distributed Cavity Phase Shift for the New Microwave Cavities of Cs Fountains at NIST

The microwave cavities of NIST-F1, the cesium fountain primary frequency standard at the National Institute of Standards and Technology (NIST), have been replaced with a new design. The distributed cavity phase (DCP) bias of the new cavity must be investigated. Here, we describe an initial study of the DCP bias using the techniques developed by Li and Gibble [Li and Gibble, Metrologia 41 (2004); Li and Gibble, Metrologia 47 (2010)]. We solve for the field distribution in the Ramsey cavity using a relatively simple 3D finite element model. Density matrix simulations using this field model suggest that the DCP errors of the new cavity design are manageably small.