Atomic fountain frequency standard have the potential to reach a frequency stability of about 10−14τ−1/2, if the interrogation oscillator frequency noise which degrades the stability via the “Dick effect” ([2, 7]) is made negligible. In this aim a Sapphire Cryogenic Oscillator (SCO) is used as very low noise frequency source σy(τ) ≤ 1 – 2 × 10−15 1 s ≪ τ ≪ 1000 s. In this paper, we describe a low phase/frequency noise flywheel sourcea for atomic fountains and other demanding metrological applications (cold atom inertial sensors, optical frequency standards, optical synthesizer based on femto-second laser).