OPERATIONAL USE OF PTB'S ATOMIC CAESIUM FOUNTAIN CSF1

摘要

The atomic fountain frequency standard CSF1 of the Physikalisch-Technische Bundesanstalt (PTB) has matured to a regularly operated primary frequency standard. During 2001, CSF1 was used to measure the TAI scale unit during five intervals of 15 or 20 days duration, showing a departure of the TAI scale unit from the SI second of a few parts in 10~(15). During three periods of simultaneous operation, CSF1 was compared to NIST-F1 of the US National Institute of Standards and Technology using GPS carrier phase technique and TWSTFT. In one case, the difference between the standards slightly exceeded the combined 1σ -measurement uncertainty, in two cases the disagreement was less significant. A free atomic time scale, TAF(PTB), has been realised since summer 2000. Its physical realisation is based on a hydrogen maser and a subsequent microphase stepper (MPS). The MPS steers the frequency of TAF(PTB) to that of CSF1. With reference to the hydrogen maser based time scale AT1E of NIST, a relative frequency instability of 1.5·10~(-15) at τ = 30 days was verified. Real time prediction of the difference TAI-TAF(PTB) has been shown to be possible with a 1σ -standard deviation of 12 ns.