Uncertainty evaluation of the atomic caesium fountain CSF1 of the PTB

A new primary frequency standard, the atomic caesium fountain CSF1, has been put into operation at the Physikalisch-Technische Bundesanstalt (PTB). Cs-133 atoms are cooled in a magneto-optical trap and in optical molasses. They are launched to a height of 39 cm above the microwave cavity centre. The resulting Ramsey resonance signal has a full-width half-maximum linewidth (FWHM) of 0.88 Hz. The first uncertainty evaluation yields a relative 1 sigma frequency uncertainty of 1.4 x 10(-15). The short-term relative frequency instability of the CSF1 for averaging time tau is typically 3.5 x 10(-13) (tau/s)(-1/2), dictated by the available quartz oscillator as the local frequency source.