Spurious microwave fields in caesium atomic beam frequency standards: symmetry considerations and model calculations

Spurious microwave fields can be a cause of systematic frequency offsets and excessive frequency instability in caesium atomic beam frequency standards. In this contribution, we present helpful results to distinguish this type of disturbance in frequency standards from others. We have treated the interaction in the Ramsey cavity and an additional interaction with a spurious microwave field inside the beam tube as weak interactions and also with realistic parameters using full quantum mechanical calculations. We obtain the clock frequency shifts in dependence on amplitude and phase of the spurious field, and on the modulation parameters