Discussion of the uncertainty budget and of long term comparison of PTB's primary frequency standards CS1, CS2 and CSF1

PTB continuously operates two primary clocks, the more than 30 year old CS1 and the CS2. The clocks' standard uncertainties (1/spl sigma/) to realize the SI second were estimated as u/sub B/(CS1)=7/spl middot/10/sup -15/ and u/sub B/(CS2)=12/spl middot/10/sup -15/. Since 2000, the caesium atomic fountain CSF1 has been operated quasi continuously during 14 intervals, each of at least 15 days duration, in the so-called routine operation mode for which an uncertainty u/sub B/(CSF1) of typically 1/spl middot/10/sup -15/ was specified. During these intervals the CS2 and the CSF1 agreed well within the uncertainty u/sub B/(CS2). On the contrary, the CS1 frequency deviates slightly more from CSF1 than u/sub B/(CS1). The /spl sigma//sub E/ of the CS2 comparison data can be explained as white frequency noise of the CS2 (calculated from the CS2 signal parameters) combined with an extra contribution of less than 1/spl middot/10/sup -15/, whereas an extra noise contribution of 3.7/spl middot/10/sup -15/ is needed to explain the /spl sigma//sub E/ of the CS1 comparison data. In view of this, the individual contributions to the clocks' uncertainty budget are analyzed.

[1]  Michel Abgrall,et al.  Evaluation des performances de la fontaine atomique PHARAO, Participation à l'étude de l'horloge spatiale PHARAO , 2003 .

[2]  Andreas Bauch,et al.  Measurement of the Frequency-Shift Due to Distributed Cavity Phase Difference in an Atomic Clock , 1985, IEEE Transactions on Instrumentation and Measurement.

[3]  A. Bauch,et al.  Long-term time comparison between frequency standards at NIST and PTB for a test of the validity of local position invariance , 2003, IEEE International Frequency Control Symposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003.

[4]  Andreas Bauch,et al.  Comparisons of the PTB primary clocks with TAI in 1999 , 2000 .

[5]  A. Makdissi,et al.  Evaluation of the accuracy of the optically pumped caesium beam primary frequency standard of BNM-LPTF , 2001 .

[6]  Andreas Bauch,et al.  Performance of the PTB reconstructed primary clock CS1 and an estimate of its current uncertainty , 1998 .

[7]  U. Hubner,et al.  Design and realization of the microwave cavity in the PTB caesium atomic fountain clock CSF1 , 2002, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[8]  A. Bauch,et al.  New experimental limit on the validity of local position invariance , 2002 .

[9]  Ph Laurent,et al.  Search for variations of fundamental constants using atomic fountain clocks. , 2003, Physical review letters.

[10]  Andreas Bauch,et al.  The Atomic Caesium Fountain CSF1 of Ptb , 2002 .

[11]  Jon H. Shirley,et al.  A new cavity configuration for cesium beam primary frequency standards , 1988 .

[12]  Andreas Bauch,et al.  Uncertainty evaluation of the atomic caesium fountain CSF1 of the PTB , 2001 .

[13]  Gerard Petit,et al.  PTB primary clocks: performance and comparison with TAI in 2000 , 2001 .

[14]  C. Thomas,et al.  Impact of new clock technologies on the stability and accuracy of the International Atomic Time TAI , 1997, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[15]  Jon H. Shirley,et al.  Accuracy evaluation of NIST-F1 , 2002 .