[time-nuts] Mercury Ion Clock

Magnus Danielson magnus at rubidium.dyndns.org
Sat Nov 1 14:05:20 EDT 2014


On 11/01/2014 05:49 PM, Jim Lux wrote:
> Having been to a few of the design reviews and such for the DSAC, and
> before, when it was called the 1 liter atomic clock, etc.
> I think one could build one *if* you have a fairly wide collection of
> skills, and you weren't hung up on it being tiny and low power, and zero
> maintenance.
> For instance, building a perfectly sealed physics package that is space
> flight compatible is non-trivial. Most of us don't have e-beam welding
> equipment sitting around (nor does JPL.. we contract that kind of stuff
> out).  As Prestage points out in the article below, they started looking
> at how they build long life Traveling Wave Tubes for space (another
> precision ion optics device), and having spent some time in various TWT
> factories over the past 15 years: there is a lot of art in the
> manufacturing process.

Ah, yes, *most* time-nuts is not aiming to shoot their clocks into deep 
space. We are satisfied to stay in geostationary orbit or lower ;-)

> http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41329/1/07-2003.pdf
> http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41395/1/08-0610.pdf
> However, if you were happy with "lab grade" construction, and you have
> the Kurt Lesker and Duniway catalogs as bedside reading, I think you'd
> have a chance.

Yes. I guess a bit of baking out the build is also to be recommended.
I guess most of us don't do vacuum in our labs, so there is a challenge 
in itself, as there is many beginners mistakes to be done there.

> The ion trap and such is a fairly straightforward thing, from what I
> understand: you need the usual vacuum pumps and such to build one.  If
> you don't want it to run for years without servicing, then issues of the
> mercury content are less important.
> (BTW, the space clock uses thermal dissociation of HgO to get the mercury)

Have tou cared to get the right isotope or do you use the natural 
abundance spreading? Hg-199 has an abundance of 16,87%.

> The PMT is an off the shelf thing. Check out the amateur built fusion
> reactor (fusor) websites on where to get PMTs and amplifiers (they're
> used behind a scintillator)

Ah yes. Got a NaI(Tl) scintilator with about 1 cm copper filter and a 
matching PMT. No amp thought, but then again, I do not know what I 
should measure with it. :)

> The 40 GHz stuff these days is not nearly as exotic as it used to be.
> The challenge might be test equipment when you're debugging your 40 GHz
> synthesis chain.

I was thinking the same, especially when consider optical clocks, then 
40 GHz isn't as esoteric. Traditional cesiums and rubidiums use a pair 
of synthesized frequencies being then sent into a step-recover diode 
inside a tuned cavity which then does the mixing and selects the right 

> I don't think it would be *easy*, but I think doable, and nothing in the
> system is particularly expensive or that exotic.  It's sort of like
> telescope building.. The raw materials to make a 18" reflector telescope
> aren't all that expensive, nor is there some secret sauce: it's just
> time to grind the mirror (and recover from mistakes) and build the system.

Would be a fun project to do, things to be learned.


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