The reason of this shift is reported in #66243. The procedure followed during the shift is reported in this git issue.
At the beginning of the shift, after the unlock, Diego called Michal and Romain beacuse DET_MAIN node got stalled (66300).
At 16.05 UTC, the interferometer locked at LN2. At 17.35 UTC, the standard SSFS noise injection was performed.
After that, at 18.12 UTC, the DAS outer ring powers were adjusted differentially. In particular, the WI outer ring power was increased by 5%, while the NI outer ring power was decreased by 5%.
| Reference | CH [W] | INNER DAS [W] | OUTER DAS [W] |
| (West) on the ITF | 0.046 | 0.150 | 1.59 → 1.59*(1+5/100)= 1.68 |
| (West) on the pick-off | 0.284 | 0.025 | 0.26 → 0.27 |
| (North) on the ITF | 0.104 | 0.340 | 3.68 → 3.68*(1-5/100)=3.5 |
| (North) on the pick-off | 0.635 | 0.055 | 0.61 → 0.57 |
After one hour we started to see a growing oscillation at low frequency, in particular we checked that it was the usual interaction between PR and BS TX. SO we tried to move the crossing point of the two error signals. WE changed the weight from 0.67 to 0.82 and the oscillation got damped. After 2 hours we repeated the SSFS noise injections and Figure 1 shows the change on the coupling of the SSFS to DARM between before and after the DAS step.
Then we went to LN3 and we stayed there for 1 hour, and repeated the SSFS noise injection. After this injection Ilaria put back the initial DAS values (22.15 - 22.18 UTC).
