Hi,
There is an overemphasis on the atom being used, and especially on
cesium as that is what is used for SI definition. However, actual
implementation means actual physical devices, and the physical devices
have a physics package, for which details will be important to the
actual performance. Various atoms have been more or less well adapted to
different types of physical package types. The beam type of device can
be made to have very little perturbation, and cesium was well suited for
that, while rubidium ended up being very well suited for the gas cell
type. The CSAC is really a cesium based gas cell, but the original
benefit of rubidium filtered optical pumping has been replaced with
semiconductor lasers for pumping. Today both cesium and rubidium gas
cells with the same mechanism exists. With gas cell you get wall shift
from atoms banging around the wall, but also gas shift as buffer gas
makes the atoms hit the buffer gas most of the times. With a bit of
selection of gas mixture, these can be made to balance each other.
So, what is the claim to fame for CSAC? It's actually not being cesium,
but for the stability it provides for the small amount of power it
consumes. That's also where it finds actual applications. If you can
afford more power, there is cheaper alternatives available.
Cheers,
Magnus
Den 2021-11-27 kl. 23:28, skrev Bob kb8tq:
Hi
The CSAC is not a cesium in the conventional sense. It is much closer to
a telecom Rb than anything else. There likely are telecom Rb’s that would
do a better job. Would they do a good enough job? …. likely not ….
Bob
On Nov 27, 2021, at 5:11 PM, Lux, Jim <[email protected]> wrote:
On 11/27/21 12:37 PM, Thomas Valerio wrote:
I think that Tom's GREAT adventure is kind of what sealed the deal making
me a time-nut or at least a time-nuts lurker, a lot of this stuff is still
little over my head, but I keep reading.
If anyone is inclined and has the clocks and the kids ( I don't have
either ), there is always Mount Evans and Pikes Peak, although you may
have to leave the clocks behind overnight. Mount Evans is still on my
bucket list but without clocks and two or three days of time to monitor
them, I don't think I will be doing the Mount Evans edition of GREAT. For
anyone that is flush enough to afford or can beg, borrow or steal access
to a Microsemi chip scale atomic clock, I think a Mount Evans edition
would be an awesome addition to Tom's original work.
Thomas Valerio
I don't think a CSAC would be good enough.
Tom's experiment was 22 ns out of 42 hours or about 1.45E-13. That's quite a
bit smaller than a CSAC adev over that period.
There's a variety of roads that go to ~12,000 ft in Colorado, about ~10,000 in CA
(Tioga Pass isn't closed yet), so you can get about 3x change, but still you're
talking <1E-12.
Mammoth Mtn has a gondola to the top, but it's only 11,000. There may be a ski
resort in CO that's higher.
For newcomers to time-nuts, Andy is asking about my DIY gravitational
time dilation experiment(s).
> What am I missing?
It looks like you used the wrong value (or wrong units) for "h".
The summit of Mt Rainier is 14411 ft (4400 m), but the highest point on
Mt Rainier that is accessible by road is the Paradise visitors center at
5400 ft. Our house is at 1000 ft elevation so the net difference in
elevation of the clocks was 4400 ft (1340 m).
The clock(s) on the mountain ran fast by gh/c² = 9.8 × 1340 / (3e8)² =
1.5e-13. Fast clocks gain time. We stayed for about 42 hours so the net
time dilation was 42×3600 × gh/c² = 22 ns.
----
For more information see the Project G.R.E.A.T. 2005 page:
http://leapsecond.com/great2005/
Better yet, these two recent talks from 2018 and 2020 cover all 3 GREAT
experiments:
<http://web.stanford.edu/group/scpnt/pnt/PNT18/presentation_files/I08-VanBaak-GPS_Flying_Clocks_and_Relativity.pdf>
<http://leapsecond.com/ptti2020/2020-PTTI-tvb-Atomic-Timekeeping-Hobby.pdf>
Lots of time nutty photos in both of those!
/tvb
On 11/27/2021 7:33 AM, Andy Talbot wrote:
Just been reading your adventures with 3 Cs clocks, a mountain and 3
kids,
but I can't make the estimate of time dilation work out.
You measured ~ 23ns and say it agrees with calculation
The equation quoted in a related reference, for "low elevations" is
g.h/c²
which if you plug in g = 9.81 m/s² and h = 4300m for Mt Rainer gives
an
expected value of 4.7 * 10^-16.
Over 2 days, 2 * 86400s, that would be 81 ns in total, four times your
value
What am I missing?
Was just speculating what Ben Nevis at a mere 1340m height might offer
Andy
www.g4jnt.com
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