[time-nuts] vs Hg ion? Re: GPS clock stabilitiy, Rb vs Cs

[Tom Knox]

The idea of a Mercury Ion clocks started about 2000 and from about 2005 until recently has held the title of worlds most accurate clock.
Approx 1 sec per 1.6 billion years the last I heard. At the heart is a single trapped mercury atom. Jim Bergquist at NIST was one of those that lead the development.
This link has the basics: http://tf.nist.gov/general/pdf/1957.pdf.   I want two.

Thomas Knox


1-303-554-0307

> Date: Sun, 5 May 2013 06:59:12 -0700
> From: jimlux at earthlink.net
> To: time-nuts at febo.com
> Subject: [time-nuts] vs Hg ion? Re:  GPS clock stabilitiy, Rb vs Cs
> 
> On 5/5/13 1:48 AM, Magnus Danielson wrote:
> > On 05/05/2013 10:05 AM, Attila Kinali wrote:
> >> On Sat, 4 May 2013 12:36:20 -0700
> >> "Tom Van Baak (lab)"<tvb at leapsecond.com>  wrote:
> >>
> >>> Rule of thumb: quartz is best short term, Rb or H-maser mid-term,
> >>> and Cs by far the best long-term.
> >>
> >> Ah.. so it's a fundamental limitation. And i was looking for something
> >> GPS specific.
> >>
> >> Any references i could read on those limitations? A quick google
> >> did not produce any good results.
> >
> > There is a handful of references but picking up a book like "Quantum
> > Leap" is a good start.
> >
> > Quartz is a bit of (syntetic) rock, cut at some angle(s), cleaned,
> > mounted in some hermetic sealed chamber with residue dirt, and mounting
> 
> <snip>
> 
> >
> > For rubidium gas-cell, there is a bunch of systematics, including
> <snip>
> 
> > The caesium atomic beam does not have wall-shifts, but rather it has
> > much lower systematics. One of the major onces being magnetic field.
> <snip>
> 
> > The above is a summary of things collected from a variety of sources,
> > but I think this coarse walk-through of issues gives some insight as to
> > what issues pops up where and the milage vary a lot within each group.
> > Modern high-performance rubidium gas-cells outperform the early
> > caesiums, high-performance crystals outperform several rubidiums.
> > The HP5065A is an example of an old clock with really good performance,
> > so modern is not everything, and the modern compact telecom rubidiums
> > and for that mater CSAC is more space/power oriented than ultimate
> > performance of the technology as such.
> 
> 
> I wonder where mercury ion fits in the scheme of things, since that's 
> where we're spending some money for spacecraft applications right now. 
> It's supposed to be orders of magnitude better than Rb.
> 
> 
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