Towards a solution to the field uniformity problem in the high field cesium beam frequency standard

The most severe requirement, with respect to accuracy, for a Cesium beam primary frequency standard operating in the high C-field configuration, is the uniformity of the C-field along the atomic trajectory. In fact, the latter determines the size of the average quadratic Zeeman shift, which is the biggest cause of uncertainty in such a standard: a uniformity of the order of 10^-6 is required to guarantee an accuracy in the low 10^-14. Such a high level of uniformity is very difficult to reach, and even more difficult to guarantee during operation by measurements taken during assembly, which is the usual procedure for primary standards operated at low field. An avenue towards the solution of this problem is offered, in the high C-field configuration, by the use of a multilambda Rabi cavity. In fact, because of the high operating field, even at relatively high uniformity levels the absolute spatial field variations may be big enough to totally separate in frequency the atomic signals of the same field dependent transition excited in different locations along the beam within the Rabi cavity. Corrections of the field uniformity can then be made during tube operation, and monitored by looking in real time on a scope at the shape of the field dependent transition