Measurements of the distributed cavity phase shift in the LNE-SYRTE FO2 fountain

We report measurements and calculations of distributed cavity phase errors in an atomic fountain clock. We isolate even and odd symmetry contributions to the distributed cavity phase shift and measure their characteristic power dependences. The measurements and model largely agree with no free parameters. Verification of the model will enable a reduction of the distributed cavity phase uncertainty for current clocks and validates new cavity designs that have minimal phase variations.