Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Magnus Danielson]

Hi,

On 04/12/2017 01:17 PM, Bob kb8tq wrote:

Hi

If you take a look at the standard weekly publications, the GPS system runs on 
Rb’s.
There is always one sat that has a Cs turned on. That’s been true as long as 
they
have been running the system. The simple answer for that choice is that the Rb’s
are easier to predict (better short term to medium term performance).

The Cs standards were originally on board to allow operation in the event that 
the ground control
system was unable to upload to the constellation. There also was concern in the 
80’s
about the reliability of the Rb’s. The configuration has stayed the same, 
despite the
Rb’s being the main standard used.

Number of standards on board in the block IIF sats was 2 Rb’s and 2 Cs’s. That 
is a
petty typical “redundant” approach.


For the block IIR they new cesium failed to get space-qualification, so 
those birds only fly rubidium.


Cheers,
Magnus
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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Magnus Danielson]

Hi,

On 04/12/2017 12:15 AM, Richard (Rick) Karlquist wrote:

The "magic" of Rb in a gas cell standard is that you
can make an optical filter cell out of radioactive
Rb87 isotope that allows you to selectively optically pump
to the quantum level you need.  It is just "luck"
that the absorption line falls where you need it.
And the RF pumping is at a doable 6.8 GHz.


Indeed. Rubidium was more suitable for optical pumping, so that is why 
it is suitable to build gas-cells, as it is relatively easy to do.


Rb-85 and Rb-87 has interesting properties in their D1 and D2 lines, so 
by matching temperature you can filter out one of the D-lines with the 
other isotope and that way get pumping action into one of two states. 
The better pumping, the better S/N.



I think the CSAC uses lasers so all of this doesn't
apply.


Correct.


Cesium of course is part of the definition of the second,
so it's good to use for that reason.

It is a different discussion as to why Cs was chosen
to define the second, but the line being at 9.2 GHz might have had
something to do with it.  That's a doable frequency in terms
of technology 60 years ago.


For a gas-cell the Cs being a reference is however moot, since the wall 
pull and gas pull makes such systematics effects that it is not 
suitable. For a small gas-cell the use of Cesium or Rubidium is more 
about practicality. Several other projects work with rubidiums.


Thallium was competing with cesium for some time, but the higher 
frequency made it impractical, and also considering that ionization was 
harder was an issue back then, giving lower signal to noise. The 
frequency of Thallium is not an issue today, and with modern laser 
technology ionization could be replaced by optical detection. I haven't 
checked the optical frequencies for Thallium and it's suitability with 
modern lasers, but the selection is much wider now.


Turns out that in the laser-cooled fountains, rubidium respond better 
than cesium due to the smaller cross-section, making likelihood for 
collisions and loss of state less, causing less frequency pull due to 
this effect.


Cheers,
Magnus
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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Ole Petter Rønningen]

A little of the thinking, and a bit of the history of the rb v cs is in "CESIUM 
AND RUBIDIUM FREQUENCY STANDARDS STATUS AND PERFORMANCE ON THE GPS PROGRAM"

http://www.stanson.ch/files/GPS/Vol%2027_14.pdf

Ole

> Den 12. apr. 2017 kl. 08.41 skrev Hal Murray :
> 
> 
> jim...@earthlink.net said:
>> If there's nothing folks are aware of, I'll probably see if I can find  some
>> nice schematic pictures of a Cs Beam, a gas cell, and an Hg ion  trap, and
>> then a AVAR plot or something. 
> 
> I think the GPS satellites have 3 Cs and 2 Rbs.  There might be an 
> interesting story about why they decided to split their eggs into two baskets.
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Bob kb8tq]

Hi

If you take a look at the standard weekly publications, the GPS system runs on 
Rb’s.
There is always one sat that has a Cs turned on. That’s been true as long as 
they
have been running the system. The simple answer for that choice is that the Rb’s
are easier to predict (better short term to medium term performance). 

The Cs standards were originally on board to allow operation in the event that 
the ground control
system was unable to upload to the constellation. There also was concern in the 
80’s 
about the reliability of the Rb’s. The configuration has stayed the same, 
despite the
Rb’s being the main standard used. 

Number of standards on board in the block IIF sats was 2 Rb’s and 2 Cs’s. That 
is a 
petty typical “redundant” approach. 

Bob





> On Apr 12, 2017, at 2:41 AM, Hal Murray  wrote:
> 
> 
> jim...@earthlink.net said:
>> If there's nothing folks are aware of, I'll probably see if I can find  some
>> nice schematic pictures of a Cs Beam, a gas cell, and an Hg ion  trap, and
>> then a AVAR plot or something. 
> 
> I think the GPS satellites have 3 Cs and 2 Rbs.  There might be an 
> interesting story about why they decided to split their eggs into two baskets.
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Hal Murray]

jim...@earthlink.net said:
> If there's nothing folks are aware of, I'll probably see if I can find  some
> nice schematic pictures of a Cs Beam, a gas cell, and an Hg ion  trap, and
> then a AVAR plot or something. 

I think the GPS satellites have 3 Cs and 2 Rbs.  There might be an 
interesting story about why they decided to split their eggs into two baskets.

-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Bob kb8tq]

HI

> On Apr 11, 2017, at 5:57 PM, jimlux  wrote:
> 
> On 4/11/17 12:59 PM, Bob kb8tq wrote:
>> Hi
>> 
>> Assuming you are doing a “conventional” Rb and Cs there are a number of 
>> differences. There is the sub set of doing a gas cell based on Cs which is
>> a lot more similar to Rb. With the Cs, you are building a very complicated 
>> vacuum tube that plays with a focused beam of ions traveling in space. With 
>> the
>> Rb you have essentially a couple of odd (Rb based) "neon bulbs" that do some 
>> cute interactions optically. Making light bulbs is easier than making
>> microwave vacuum tubes. Temperature and magnetic filed mess with both 
>> systems so they need to be controlled in both cases.
>> 
>> The more subtle issue is that we have an implicit expectation of performance 
>> when we talk about an Rb or a Cs. An ADEV of 1x10^-13 at 1,000 seconds is
>> interesting. An ADEV of 1x10^-9 at 1,000 seconds is not as interesting. 
>> Going from a level of “it works” to the point that it works reasonably well 
>> is a
>> long road with lots of zigs and zags. Teams of people do indeed spend a lot 
>> of time learning where those twists in the road are. In the case of an Rb, a 
>> half
>> dozen people working full time for a decade is probably in the range. For a 
>> Cs both the group size and time frame would be longer. In both cases there is
>> a “right” mix of skills for the team members, it’s not just a body count.
>> 
> 
> Not actually building it. I was looking for something I could point people to 
> that describes (at a high level) what the difference is between the kinds of 
> references.  Just because it says "atomic clock" on it doesn't mean that 
> they're all the same.
> (I can handle explaining why their "atomic" watch isn't really an atomic 
> standard, unless they're doing the tvb arm exercises approach)
> 
> If there's nothing folks are aware of, I'll probably see if I can find some 
> nice schematic pictures of a Cs Beam, a gas cell, and an Hg ion trap, and 
> then a AVAR plot or something.
> 

Unfortunately, a lot of this boils down to “that’s how it is”. This 
implementation of that technology works best. It has something to do with the 
underlying 
physics (trapped optical ions vs gas cells). The bigger par is what the best 
design can extract from the physics. It quickly gets messy once you look under
the hood ….

Bob

> 
> 
> 
>> Bob
>> 
>>> On Apr 11, 2017, at 10:30 AM, jimlux  wrote:
>>> 
>>> I'm looking for a link to point to an explanation (at a basic level) of the 
>>> difference between Rb and Cs references, and what the tradeoffs are.
>>> I googled a bit, but all I got were some explanations of the differences in 
>>> things like vapor pressure, etc.
>>> 
>>> Wikipedia  (Atomic_clock) has some nice words, but no block diagram of the 
>>> innards, which would be nice.
>>> 
>>> And there's plenty of charts showing the relative performance of Rb and Cs, 
>>> but not with any accompanying explanation of why.
>>> 
>>> I'm looking for something a bit more detailed, but not a 20 page tutorial 
>>> on atomic clocks.
>>> 
>>> Maybe someone has seen something on a manufacturer website or something?
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
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>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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>> 
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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Bob kb8tq]

HI

> On Apr 11, 2017, at 6:15 PM, Richard (Rick) Karlquist  
> wrote:
> 
> The "magic" of Rb in a gas cell standard is that you
> can make an optical filter cell out of radioactive
> Rb87 isotope that allows you to selectively optically pump
> to the quantum level you need.  It is just "luck"
> that the absorption line falls where you need it.
> And the RF pumping is at a doable 6.8 GHz.
> 
> I think the CSAC uses lasers

Indeed the CSAC (and the NAC) use lasers rather than a multi cell approach. 
They likely are not the first devices to
do so. The CSAC is certainly the first “production” device to run on lasers. 
The claim is made that the CSAC went 
ti a Cs based gas cell partly due to the availability of lasers at the “right” 
frequency (wavelength). 

Bob


> so all of this doesn't
> apply.
> 
> Cesium of course is part of the definition of the second,
> so it's good to use for that reason.
> 
> It is a different discussion as to why Cs was chosen
> to define the second, but the line being at 9.2 GHz might have had something 
> to do with it.  That's a doable frequency in terms
> of technology 60 years ago.
> 
> Rick N6RK
> 
> On 4/11/2017 1:54 PM, jimlux wrote:
>> On 4/11/17 12:34 PM, Attila Kinali wrote:
>>> Hoi Jim,
>>> 
>>> On Tue, 11 Apr 2017 07:30:38 -0700
>>> jimlux  wrote:
>>> 
 I'm looking for a link to point to an explanation (at a basic level) of
 the difference between Rb and Cs references, and what the tradeoffs are.
 I googled a bit, but all I got were some explanations of the differences
 in things like vapor pressure, etc.
>>> 
>>> What exactly are you looking for? A comparison of Rb vapor cell
>>> standards vs Cs vapor cell standards? Or a general comparison
>>> why different kind of standards are built with Rb and Cs?
>>> 
>>> For the former, there is a paper that has some of the details
>>> why Cs was choosen over Rb for the CSAC in one of the papers.
>>> (Which I currently cannot find...)
>>> 
>>> For the latter, there is no easy answer and a lot come from
>>> technicalities (difference in handling) and what people were
>>> able to build. There are some fundamental differences in which
>>> elements get you what kind of stability for different kinds of
>>> atomic clocks, but I have seen very little on that and it's quite
>>> spread over various papers and books.
>> 
>> precisely why I asked..
>> 
>> The wikipedia article isn't bad in terms of covering the gas cell vs
>> beam in words, but I was hoping for something with pictures..
>> 
>> Encyclopedia Brittanica, perhaps.. except that they only talk about
>> caesium beam
>> 
>> 
>> 
>> 
>>> 
>>>Attila Kinali
>>> 
>> 
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>> 
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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[jimlux]

On 4/11/17 12:59 PM, Bob kb8tq wrote:

Hi

Assuming you are doing a “conventional” Rb and Cs there are a number of 
differences. There is the sub set of doing a gas cell based on Cs which is
a lot more similar to Rb. With the Cs, you are building a very complicated 
vacuum tube that plays with a focused beam of ions traveling in space. With the
Rb you have essentially a couple of odd (Rb based) "neon bulbs" that do some 
cute interactions optically. Making light bulbs is easier than making
microwave vacuum tubes. Temperature and magnetic filed mess with both systems 
so they need to be controlled in both cases.

The more subtle issue is that we have an implicit expectation of performance 
when we talk about an Rb or a Cs. An ADEV of 1x10^-13 at 1,000 seconds is
interesting. An ADEV of 1x10^-9 at 1,000 seconds is not as interesting. Going 
from a level of “it works” to the point that it works reasonably well is a
long road with lots of zigs and zags. Teams of people do indeed spend a lot of 
time learning where those twists in the road are. In the case of an Rb, a half
dozen people working full time for a decade is probably in the range. For a Cs 
both the group size and time frame would be longer. In both cases there is
a “right” mix of skills for the team members, it’s not just a body count.



Not actually building it. I was looking for something I could point 
people to that describes (at a high level) what the difference is 
between the kinds of references.  Just because it says "atomic clock" on 
it doesn't mean that they're all the same.
(I can handle explaining why their "atomic" watch isn't really an atomic 
standard, unless they're doing the tvb arm exercises approach)


If there's nothing folks are aware of, I'll probably see if I can find 
some nice schematic pictures of a Cs Beam, a gas cell, and an Hg ion 
trap, and then a AVAR plot or something.






Bob


On Apr 11, 2017, at 10:30 AM, jimlux  wrote:

I'm looking for a link to point to an explanation (at a basic level) of the 
difference between Rb and Cs references, and what the tradeoffs are.
I googled a bit, but all I got were some explanations of the differences in 
things like vapor pressure, etc.

Wikipedia  (Atomic_clock) has some nice words, but no block diagram of the 
innards, which would be nice.

And there's plenty of charts showing the relative performance of Rb and Cs, but 
not with any accompanying explanation of why.

I'm looking for something a bit more detailed, but not a 20 page tutorial on 
atomic clocks.

Maybe someone has seen something on a manufacturer website or something?
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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Richard (Rick) Karlquist]

The "magic" of Rb in a gas cell standard is that you
can make an optical filter cell out of radioactive
Rb87 isotope that allows you to selectively optically pump
to the quantum level you need.  It is just "luck"
that the absorption line falls where you need it.
And the RF pumping is at a doable 6.8 GHz.

I think the CSAC uses lasers so all of this doesn't
apply.

Cesium of course is part of the definition of the second,
so it's good to use for that reason.

It is a different discussion as to why Cs was chosen
to define the second, but the line being at 9.2 GHz might have had 
something to do with it.  That's a doable frequency in terms

of technology 60 years ago.

Rick N6RK

On 4/11/2017 1:54 PM, jimlux wrote:

On 4/11/17 12:34 PM, Attila Kinali wrote:

Hoi Jim,

On Tue, 11 Apr 2017 07:30:38 -0700
jimlux  wrote:


I'm looking for a link to point to an explanation (at a basic level) of
the difference between Rb and Cs references, and what the tradeoffs are.
I googled a bit, but all I got were some explanations of the differences
in things like vapor pressure, etc.


What exactly are you looking for? A comparison of Rb vapor cell
standards vs Cs vapor cell standards? Or a general comparison
why different kind of standards are built with Rb and Cs?

For the former, there is a paper that has some of the details
why Cs was choosen over Rb for the CSAC in one of the papers.
(Which I currently cannot find...)

For the latter, there is no easy answer and a lot come from
technicalities (difference in handling) and what people were
able to build. There are some fundamental differences in which
elements get you what kind of stability for different kinds of
atomic clocks, but I have seen very little on that and it's quite
spread over various papers and books.


precisely why I asked..

The wikipedia article isn't bad in terms of covering the gas cell vs
beam in words, but I was hoping for something with pictures..

Encyclopedia Brittanica, perhaps.. except that they only talk about
caesium beam






Attila Kinali



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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[jimlux]

On 4/11/17 12:34 PM, Attila Kinali wrote:

Hoi Jim,

On Tue, 11 Apr 2017 07:30:38 -0700
jimlux  wrote:


I'm looking for a link to point to an explanation (at a basic level) of
the difference between Rb and Cs references, and what the tradeoffs are.
I googled a bit, but all I got were some explanations of the differences
in things like vapor pressure, etc.


What exactly are you looking for? A comparison of Rb vapor cell
standards vs Cs vapor cell standards? Or a general comparison
why different kind of standards are built with Rb and Cs?

For the former, there is a paper that has some of the details
why Cs was choosen over Rb for the CSAC in one of the papers.
(Which I currently cannot find...)

For the latter, there is no easy answer and a lot come from
technicalities (difference in handling) and what people were
able to build. There are some fundamental differences in which
elements get you what kind of stability for different kinds of
atomic clocks, but I have seen very little on that and it's quite
spread over various papers and books.


precisely why I asked..

The wikipedia article isn't bad in terms of covering the gas cell vs 
beam in words, but I was hoping for something with pictures..


Encyclopedia Brittanica, perhaps.. except that they only talk about 
caesium beam







Attila Kinali



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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Attila Kinali]

Hoi Jim,

On Tue, 11 Apr 2017 07:30:38 -0700
jimlux  wrote:

> I'm looking for a link to point to an explanation (at a basic level) of 
> the difference between Rb and Cs references, and what the tradeoffs are.
> I googled a bit, but all I got were some explanations of the differences 
> in things like vapor pressure, etc.

What exactly are you looking for? A comparison of Rb vapor cell
standards vs Cs vapor cell standards? Or a general comparison
why different kind of standards are built with Rb and Cs?

For the former, there is a paper that has some of the details
why Cs was choosen over Rb for the CSAC in one of the papers.
(Which I currently cannot find...)

For the latter, there is no easy answer and a lot come from
technicalities (difference in handling) and what people were
able to build. There are some fundamental differences in which
elements get you what kind of stability for different kinds of
atomic clocks, but I have seen very little on that and it's quite
spread over various papers and books.

Attila Kinali

-- 
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
 -- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] a link to a explanation of Rb vs Cs?

[Bob kb8tq]

Hi

Assuming you are doing a “conventional” Rb and Cs there are a number of 
differences. There is the sub set of doing a gas cell based on Cs which is 
a lot more similar to Rb. With the Cs, you are building a very complicated 
vacuum tube that plays with a focused beam of ions traveling in space. With the
Rb you have essentially a couple of odd (Rb based) "neon bulbs" that do some 
cute interactions optically. Making light bulbs is easier than making 
microwave vacuum tubes. Temperature and magnetic filed mess with both systems 
so they need to be controlled in both cases. 

The more subtle issue is that we have an implicit expectation of performance 
when we talk about an Rb or a Cs. An ADEV of 1x10^-13 at 1,000 seconds is 
interesting. An ADEV of 1x10^-9 at 1,000 seconds is not as interesting. Going 
from a level of “it works” to the point that it works reasonably well is a 
long road with lots of zigs and zags. Teams of people do indeed spend a lot of 
time learning where those twists in the road are. In the case of an Rb, a half 
dozen people working full time for a decade is probably in the range. For a Cs 
both the group size and time frame would be longer. In both cases there is 
a “right” mix of skills for the team members, it’s not just a body count. 

Bob

> On Apr 11, 2017, at 10:30 AM, jimlux  wrote:
> 
> I'm looking for a link to point to an explanation (at a basic level) of the 
> difference between Rb and Cs references, and what the tradeoffs are.
> I googled a bit, but all I got were some explanations of the differences in 
> things like vapor pressure, etc.
> 
> Wikipedia  (Atomic_clock) has some nice words, but no block diagram of the 
> innards, which would be nice.
> 
> And there's plenty of charts showing the relative performance of Rb and Cs, 
> but not with any accompanying explanation of why.
> 
> I'm looking for something a bit more detailed, but not a 20 page tutorial on 
> atomic clocks.
> 
> Maybe someone has seen something on a manufacturer website or something?
> ___
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[time-nuts] a link to a explanation of Rb vs Cs?

[jimlux]

I'm looking for a link to point to an explanation (at a basic level) of 
the difference between Rb and Cs references, and what the tradeoffs are.
I googled a bit, but all I got were some explanations of the differences 
in things like vapor pressure, etc.


Wikipedia  (Atomic_clock) has some nice words, but no block diagram of 
the innards, which would be nice.


And there's plenty of charts showing the relative performance of Rb and 
Cs, but not with any accompanying explanation of why.


I'm looking for something a bit more detailed, but not a 20 page 
tutorial on atomic clocks.


Maybe someone has seen something on a manufacturer website or something?
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