PARCS magnetic field measurement: low frequency Majorana transitions and magnetic field inhomogeneity

Knowledge of the magnetic field is required to determine the quadratic Zeeman bias of a cesium frequency standard. The small magnetic fields (C-field) used in PARCS (PARCS is the primary atomic reference clock in space project), may have sufficient inhomogeneity that it is not practical to measure the field by observing Ramsey fringes on a field-sensitive hyperfine line at low launch velocities. An alternative method is to observe low-frequency (Majorana) transitions among the Zeeman sublevels. However, this method does not average the C-field in the same way as Ramsey excitation. We have computed the error incurred in using this method for some simple models of inhomogeneity. We have then estimated the field homogeneity requirements needed for this method to produce adequate results. Experiments with the NIST cesium fountain are in qualitative agreement.