PHARAO Microwave Source: A short term frequency stability of 7.10−14 at 1 second

The PHARAO microwave source development is close to be completed. The tests performed on both the EQM and the FM demonstrated high performances, in terms of phase noise, spectral purity and electromagnetic leakage, compatible with the cold atoms clock accuracy objectives, within the constrains of the space mission. A short term stability of 7.10^-14τ^-1/2 has been obtained when operating the SH EQM with an atomic fountain. Extensive tests showed that the delivered interrogation signal is free of phase transient during nominal cycling operation, except because of the preparation pulse command. This defect is 10 times smaller on the FM. Furthermore, any effect of the command will cancel out, thanks to a blanking procedure applied in the ACES FCDP phase lock loop. The next step is the tests of the ACES loop at CNES Toulouse using SH EQM, FCDP EM and a CSO. Later, the SH will be integrated in PHARAO, and new measurements of its performances will be performed to validate the autocompatibility with the other subsystems, and after, at ACES level. Presently, the SH FM is upgraded with a USO having a lower acceleration sensitivity, to reduce the effect of the microvibrations onboard the ISS.