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

Magnus Danielson magnus at rubidium.dyndns.org
Sun May 5 13:01:01 EDT 2013

Hi Jim,

On 05/05/2013 03:59 PM, Jim Lux wrote:
> On 5/5/13 1:48 AM, Magnus Danielson wrote:
>> 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.

Mercury standards is of the ion trap variety. It has about 40,5 GHz of 
frequency, very high Q due to long unperturbed observation-time and also 
cool due to ion locking which reduces doppler shifts as well as thermal 
shift. If you also cool the ion trap physics to low temperature, the 
black body radiation shift can be reduced significantly. Ion traps can 
also be combined with laser cooling.

Ion traps is the new and fancy stuff in a historical perspective. HP did 
an attempt to build a commercial device as I recall it. Would not mind 
having one.

I think it is an interesting addition to the traditional mix. It 
achieves very high stability for the size. The CSAC is really a gas cell 
like rubidium, with similar issues. The ion trap takes a different route 
to the size issue. It has it's own set of challenges, but toss in a bit 
of engineering and they can be mastered. It has the potential to replace 
caesium beams in many applications.

It would be interesting to see if your effort on space qualified ion 
traps spills over to the commercial market. If you get spare samples, I 
can give you an address to send them. ;-)


More information about the time-nuts mailing list