This morning, we first checked that the CO2 actuator powers were still consistent with the values set last week, based on the OSCAR simulations and summarized in the table below:
| OSCAR simulation Starting point | CH [W] | INNER DAS [W] | OUTER DAS [W] | |
| W | on the ITF | 0.022 | 0 | 0.4 |
| on the pickoff | 0.135 | 0 | 0.065 | |
| N | on the ITF | 0.022 | 0.15 | 0.6 |
| on the pickoff | 0.135 | 0.024 | 0.098 |
Only a small adjustment of the NI CH power was needed, probably due to the recent interventions on the cooling system. At the end of the check, all the CO2 flip mirrors were closed again.
A first attempt to reach CARM NULL was performed around 08:10 UTC, but it was not successful. No clear evidence of PA was observed on the ITM thermal cameras.
We therefore decided to return to CITF and proceed with the switching ON of the CO2 actuators. CITF 1F was reached at around 08:44 UTC, with the following initial sideband levels:
-
112 MHz: 0.027 mW
-
12 MHz: 0.051 mW
At 08:45 UTC, the DAS flip mirrors were opened, with the powers reported in the table above. The evolution of the sideband levels was then monitored for almost two hours. A general worsening was expected with the DAS actuators ON alone.
After about one hour, at 09:55 UTC, the 56 MHz and 6 MHz sideband levels had decreased by approximately 30% and 20%, respectively. We agreed to manually unlock the interferometer at 10:10 UTC.
The ITF returned to CITF 1F at 10:20 UTC, with the following sideband levels:
-
112 MHz: 0.0195 mW (-27%)
-
12 MHz: 0.0355 mW (-30%)
The levels were then quite stable. The trend during this first period is shown in Figure 1.
At 10:34 UTC, the CH flip mirrors were opened, again with the powers reported in the table above. The sideband levels increased almost immediately. Already after about 20 minutes, at 10:55 UTC, they had nearly recovered their initial values.
After the lunch break, some adjustment of the PR angular loop gain was needed to allow the ITF to lock again in CITF 1F, which was achieved at around 12:05 UTC. The sideband levels then reached:
-
112 MHz: 0.0305 mW (+12%)
-
12 MHz: 0.0544 mW (+7%)
The trend during this second period is shown in Figure 2.
Just before the Daily Meeting, the first attempts to reach CARM NULL started.
The activity continued with the afternoon shift.
