Today, we performed two DAS steps to induce differential RoC variations between the ITMs. Specifically, the DAS powers were adjusted to produce an estimated RoC change of +1.5 m on one ITM and -1.5 m on the other, and vice versa.

The initial configuration of the CO2 actuators remains identical to yesterday evening's and is detailed in the table below:

When we arrived in the Control Room, the ITF had been locked at CARM_NULL_1F since 06:50 UTC. Manuel adjusted the alignment around 07:15 UTC, after which we proceeded with the DAS steps as follows:

07:45 UTC STEP 5
NI DAS IN and OUT -4%
WI DAS OUT +4% (DAS IN OFF) 

Just after this step, Manuel adjusted the lines in 69835.

12:16 UTC STEP 6
NI DAS IN and OUT +8%
WI DAS OUT -8%

Before the Daily Meeting, as about an hour was still available, Paolo proposed re-exploring the effect of the beam position on the ITMs via PR alignment. Paolo, Manuel, and Piernicola used the remaining time for this test (a dedicated log entry will follow). We intentionally chose not to restore the TCS settings immediately, as the system was still reasonably close to optimal conditions and another TCS change would have triggered a long thermal transient. 

None of the RoC differential steps yielded significant positive effects (see Fig. 1), so we agreed to restore the initial configuration of the CO2 actuators, but we performed the step just after a test on the SHUTTER_OPEN had been performed (see ISC entry for details, 69839).

14:06 UTC STEP 7 (equivalent to the resulting configuration after the STEP 4).
NI DAS IN and OUT -4%
WI DAS OUT +4%

At 14.10 UTC, the ITF unlocked due to a glitch on one of the ETMs. The CARM_NULL_1F state was acquired again at 14:42 UTC.


Between 15:25 UTC and 15:40 UTC, we began increasing the injected power in the following steps: 11.2 W → 12.6 W → 16.05 W (a total variation of approximately 4.85 W).

Since the power variation was larger than intended, the stability of the lock rapidly degraded, requiring prompt adjustment of the CO2 compensation.

We roughly estimated the power variation in the arms to be approximately +37% and performed a common DAS step of the same magnitude; furthermore, we opened the WI DAS IN flip mirror (at the minimum power value).

15:55 UTC STEP 8
NI DAS IN and OUT +37%
WI DAS OUT +37%
WI DAS IN open at minimum power

The compensation was good enough in CITF, and the SB levels were high enough to attempt going further. We therefore proceeded with the lock acquisition as reported in the ISC entry (69839) and managed to recover CARM_NULL_1F at the higher injected power around 18:45 UTC.

The final TCS power configuration is reported in the following table: