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Title: Buffer gas experiments in mercury (Hg+) ion clock
Authors: Chung, Sang K.
Prestage, John D.
Tjoelker, Robert L.
Maleki, Lute
Keywords: buffer gas
mercury ion clock
Issue Date: 23-Aug-2004
Publisher: Pasadena, CA : Jet Propulsion Laboratory, National Aeronautics and Space Administration, 2004.
Citation: IEEE Ultrasonics, Ferroelectrics, and Frequency Control Society, Montreal, Canada, August 23, 2004.
Abstract: We describe the results of the frequency shifts measured from various buffer gases that might be used as a buffer gas to increase the loading efficiency and cooling of ions trapped in a small mercury ion clock. The small mass, volume and power requirement of space clock precludes the use of turbo pumps. Hence, a hermetically sealed vacuum system, incorporating a suitable getter material with a fixed amount of inert buffer gas may be a practical alternative to the groundbased system. The collision shifts of 40,507,347.996xx Hz clock transition for helium, neon and argon buffer gases were measured in the ambient earth magnetic field. In addition to the above non-getterable inert gases we also measured the frequency shifts due to getterable, molecular hydrogen and nitrogen gases which may be used as buffer gases when incorporated with a miniature ion pump. We also examined the frequency shift due to the low methane gas partial pressure in a fixed higher pressure neon buffer gas environment. Methane gas interacted with mercury ions in a peculiar way as to preserve the ion number but to relax the population difference in the two hyperfine clock states and thereby reducing the clock resonance signal. The same population relaxation was also observed for other molecular buffer gases (N<base 2> H<base 2>,) but at much reduced rate.
Appears in Collections:JPL TRS 1992+

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