NIST physicists Steve Jefferts (foreground) and Tom Heavner with the NIST-F2 cesium fountain atomic clock, a civilian time standard for the United States.

NIST-F2 is a caesium fountain atomic clock that, along with NIST-F1, serves as the United States' primary time and frequency standard.[1] NIST-F2 was brought online on 3 April 2014.[1][2]

Accuracy

NIST-F1, a cesium fountain atomic clock used since 1999, has a fractional inaccuracy (δf / f) of less than 5×10−16.

The planned performance of NIST-F2 is δf / f < 1×10−16.[3] At this planned performance level the NIST-F2 clock will not lose a second in at least 300 million years.[4]

Evaluated accuracy

The evaluated accuracy (uB) reports of various primary frequency and time standards are published online by the International Bureau of Weights and Measures (BIPM). The first in-house accuracy evaluation of NIST-F2 reported a uB of 1.1 × 10−16.[5] In March 2014 and March 2015 the NIST-F2 cesium fountain clock reported a uB of 1.5 × 10−16 in the BIPM reports of evaluation of primary frequency standards.

The last submission of NIST-F1 to BIPM TAI was February 2016.[6]

At the request of the Italian standards organization, NIST manufactured many duplicate components for a second version of NIST-F2, known as IT-CsF2 to be operated by the Istituto Nazionale di Ricerca Metrologica (INRiM), NIST's counterpart in Turin, Italy.[1] As of February 2016 the IT-CsF2 cesium fountain clock started reporting a uB of 1.7 × 10−16 in the BIPM reports of evaluation of primary frequency standards.[7][8]

References

  1. 1 2 3 NIST Launches a New U.S. Time Standard: NIST-F2 Atomic Clock
  2. ↑ First Accuracy Evaluation of NIST-F2, T. P. Heavner, S. R. Jefferts, J. H. Shirley, T. E. Parker, E. A. Donley, N. Ashby, S. Barlow, F. Levi, and G. Costanzo, May 2014
  3. ↑ Jefferts, Steven R.; Heavner, Thomas P.; Parker, Thomas E.; Shirley, Jon H. (September 2007). NIST Cesium Fountains — Current Status and Future Prospects (PDF). International School and Conference on Optics and Optical Materials, ISCOM07. Acta Physica Polonica A. Vol. 112, no. 5. Belgrade, Serbia. pp. 759–767. doi:10.1117/12.734965. Also available from NIST directly.
  4. ↑ "Time gets an upgrade". New Scientist. 12 April 2014. p. 7.
  5. ↑ Heavner T P, Donley E A , Levi F, Costanzo G, Parker TE, Shirley J H, Ashby N, Barlow S and Jefferts SR, “First accuracy evaluation of NIST-F2,” 2014 Metrologia 51, 174–182, May 2014
  6. ↑ "BIPM - Time Department FTP server". www.bipm.org. Retrieved 2019-03-22.
  7. ↑ February 2016 IT-CsF2 TAI evaluation
  8. ↑ June 2018 IT-CsF2 TAI evaluation
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