NIST F1 and F2

T. P. Heavner, T. E. Parker, J. H. Shirley, P. Kunz, and S. R. Jefferts

Abstract:	The National Institute of Standards and Technology operates a cesium fountain primary frequency standard, NIST-F1, which has been contributing to International Atomic Time (TAI) since 1999. During the intervening 11 years, we have improved NIST-F1 so that the uncertainty is currently [see paper] dominated by uncertainty in the blackbody-radiation-induced frequency shift. In order to circumvent the uncertainty associated with the blackbody shift, we have built a new fountain, NIST-F2, in which the microwave interrogation region is cryogenic (80 K), reducing the blackbody shift to negligible levels. We briefly describe here the series of improvements to NIST-F1 that have allowed its uncertainty to reach the low 10^-16 level and present early results from NIST-F2.
Published in:	Proceedings of the 42nd Annual Precise Time and Time Interval Systems and Applications Meeting November 15 - 18, 2010 Hyatt Regency Reston Town Center Reston, Virginia
Pages:	457 - 464
Cite this article:	Heavner, T. P., Parker, T. E., Shirley, J. H., Kunz, P., Jefferts, S. R., "NIST F1 and F2," Proceedings of the 42nd Annual Precise Time and Time Interval Systems and Applications Meeting, Reston, Virginia, November 2010, pp. 457-464.
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