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Reports until 11:38, Thursday 05 January 2023
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camilla.compton@LIGO.ORG - posted 11:38, Thursday 05 January 2023 - last comment - 13:48, Friday 06 January 2023(66617)
Long CO2 tests over the break

WP 10894. Over the break we had 24hour CO2 tests with both annular and central masks to understand time constants effecting our circulating power transient alog 66548.

Attaching plots. CO2X Annular 4.7W, Central 3.0W. CO2Y Annular 4.2W, Central 3.3W. 

Some interesting things:

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camilla.compton@LIGO.ORG - 13:09, Friday 06 January 2023 (66680)

Elenna was questioning how long cool down takes. When the annular CO2 is turned off it takes 1 hour for spherical power to stabilize (right plot). Central CO2 is much slower, it takes >4 hours for spherical power to stabilize but it keeps drifting after this time. Plot attached.

Images attached to this comment
aidan.brooks@LIGO.ORG - 13:31, Friday 06 January 2023 (66681)

There is a much longer time constant for the ITM surface curvature change. The CO2 laser heats the CP, th CP couples heat to the ITM and the HR surface becomes more curved. Modeling in COMSOL suggests that the 1/e time constant is about 2E4s. The attached images show (a) the configuration modeled in COMSOL - with 1W CO2 heat applied to the CP and (b) the change in the ITM ROC vs time after the CO2 laser is turned on at t=0s.

Configuration

 

Change in ROC vs time

 

Images attached to this comment
aidan.brooks@LIGO.ORG - 13:48, Friday 06 January 2023 (66683)

Due to the linearity of the system, the cooldown will be the reverse of the above scenario.

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