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

Tim Lister listertim at gmail.com
Wed Feb 14 21:51:10 EST 2018

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


Chris Caudle

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