Primary Frequency Standard NPL-CsF2: Optimized Operation Near the Collisional Shift Cancellation Point

We report important modifications introduced to the fountain frequency standard NPL-CsF2, both to its hardware and operation protocol. First, an additional optical pumping stage has been implemented, which has enabled the clock state populations to be efficiently accumulated and has increased the number of detected atoms by a factor of four without affecting the loading and cooling stages. Second, the operation of the fountain near the collisional shift cancellation point has been optimized which, together with the increased atom number, has led to a fourfold reduction in averaging time required to achieve a given statistical resolution, e.g., that matches the type-B uncertainty of NPL-CsF2.