[time-nuts] Team of physicists repeats tvb Project GREAT

Bob kb8tq kb8tq at n1k.org
Thu Feb 15 09:05:36 EST 2018


> On Feb 15, 2018, at 9:03 AM, jimlux <jimlux at earthlink.net> wrote:
> On 2/14/18 6:51 PM, Tim Lister wrote:
>> On Feb 14, 2018 19:47, "Chris Caudle" <chris at chriscaudle.org> wrote:
>> On Wed, February 14, 2018 7:06 pm, jimlux wrote:
>>> At substantially more expense, and with an experimental lattice clock,
>> Does that schematic figure in the paper imply that the "transportable"
>> strontium and ytterbium clocks are built into trailers instead of the
>> traditional rack enclosure?
>> Actually now that I look more closely it looks like maybe two trailers.
>> Doesn't seem like something that Jim is going to be flying any time soon.
>> Yes. From the Nature article text:
>> "The transportable 87Sr lattice clock is (compared with laboratory clocks)
>> designed to be compact, with robust optical parts12
>> <https://www.nature.com/articles/s41567-017-0042-3#ref-CR12>. The physics
>> package is less than 0.6 m3 in size, and we use laser breadboards with
>> mechanical stress-resistant fibre couplers21
>> <https://www.nature.com/articles/s41567-017-0042-3#ref-CR21>. All
>> components except the reference cavity of the interrogation laser are
>> rigidly mounted in a car trailer (size 2.2 m × 3 m × 2.2 m), and vibration
>> isolation is provided by rubber dampers. The trailer interior is
>> temperature stabilized, while the small volume of the trailer hinders air
>> exchange and generates hot spots with more than 10 K temperature rise.
>> However, the optics and the physics package are placed apart and shielded
>> from these and are stable to within 0.4 K after an initial temperature rise
>> of about 1 K. The transportable ultrastable reference cavity for the clock
>> interrogation lasers is rigidly mounted to endure transport12
>> <https://www.nature.com/articles/s41567-017-0042-3#ref-CR12>. It was placed
>> next to the trailer to avoid its performance being degraded by vibrations
>> induced in the trailer’s air conditioning system. The vibration amplitudes
>> in the trailer are a factor of ten larger than under typical laboratory
>> conditions, leading to a corresponding increase in clock instability. A
>> reference resonator with lower acceleration sensitivity or an active
>> feed-forward system may in the future remedy this inconvenience22
>> <https://www.nature.com/articles/s41567-017-0042-3#ref-CR22>."
> We have discussed the desirability of suitable caves for operation of high quality clocks many times on this list.
> Clearly this is another instance.

Search the archives for “swimming pool full of mercury” for one go around on this.


> With respect to flying such things in space - this is the continual challenge - DSAC (the trapped mercury ion clock) was a couple of benches in a special time keeping lab when I first saw it, oh, a decade ago?. It will fly later this year and it's probably about the size of an airplane carry-on.
> https://www.jpl.nasa.gov/missions/deep-space-atomic-clock-dsac/
> Cold Atom Laboratory basically takes several optical benches operated by a team of post-docs that makes Bose Einstein Condensates (BEC) and turns it into a box the size of a dorm refrigerator that goes "ping" when you press a button and makes a BEC (in either Rb or K, as you choose).
> https://coldatomlab.jpl.nasa.gov/mission/
> Just as a rule of thumb, I've found that it takes about 10-20 times the cost to get from "benchtop prototype"(TRL 5) to "flyable unit" (TRL 6), as it cost to get from idea to benchtop prototype.
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