Dick effect and cavity pulling on HORACE compact cold atom clock

HORACE is a compact cold caesium (Cs) atom clock using isotropic light cooling technique directly inside the spherical microwave cavity. It has been designed for onboard and space applications. Ultimate stability as low as 2.2 10^-13 τ^-1/2 had been demonstrated, limited by atomic shot noise and quantum projection noise. Influence of Dick effect has been studied and a compact and simple frequency synthesizer using off the shelf quartz has been realized and characterized. As atoms remain in the cavity during Ramsey sequence, long term stability evaluation focused on cavity pulling effect. This proceeding presents both the microwave synthesizer development and cavity pulling study using a tricky technique to tune the microwave cavity.