Yesterday evening we raised the WI CH power (STEP 5, around +40%) in an attempt to set the SBs level in CITF back to their maximum values, i.e. around 0.054 mW for the 6 MHz and 0.032 mW for the 56MHz. So the starting point of this morning is summarised in the table below:
| Starting Point | CH [W] | INNER DAS [W] | OUTER DAS [W] |
|---|---|---|---|
| on the ITF | 0.044 | 0 | 1.08 |
| on the pickoff | 0.272 | 0 | 0.180 |
| on the ITF | 0.031 | 0.18 | 0.72 |
| on the pickoff | 0.192 | 0.029 | 0.118 |
Also this morning we made a further action, this time on the NI CH; we performed two steps:
-
STEP 6, NI CH power +18%, at 7.23 UTC
- STEP 7, NI CH power +18%, at 7.42 UTC
Since STEP 7 decreased the 12 MHz signal, we partially reverted the change by 9% with respect to STEP 7.
After these two steps, we resumed the lock acquisition attempts up to CARM NULL. After several attempts, which consistently unlocked at the same stage of the lock acquisition, the ISC team solved the issue by adjusting some lock acquisition parameters.
At 08:31 UTC, CARM_NULL_1F was reached and the lock lasted for about 30 minutes.
Figure 1 shows a comparison between this CARM_NULL_1F lock (08:31 UTC, lasting about 30 min, blue and orange lines) and the one obtained yesterday (17/09 at 14:14 UTC, lasting about 25 min, purple lines). The DAS STEP3 improved the sideband level, as can be seen from the comparison.
After the 08:31 UTC lock, we were not able to lock again due to a vertical oscillation of the PR mirror at around 11 Hz, similar to the one observed yesterday (69770). We therefore called Paolo for support.
At 10:38 UTC, following Paolo's indications, Diego managed to reach CARM_NULL_1F again.
From this point on, the CARM_NULL_1F lock became reasonably reproducible. Thanks to Diego, we also recovered the automation for the gentle unlock. After a few trials, we were able to perform the planned HWS-INJ measurements, manually unlocking the interferometer when needed.
A PA signature is visible in the HWS-INJ maps in two different measurements: during the lock acquisition (heating phase) and after the unlock from CARM NULL (cooling phase), as shown in Fig. 2. In the same figure, the CH measurement reported in entry 69694 is shown as a reference for the mirror center. From this preliminary comparison, the PA appears to be reasonably close to the center of the mirror. A more detailed analysis of the acquired data will follow.
We left the following TCS settings:
|
|
| CH [W] | INNER DAS [W] | OUTER DAS [W] |
|---|---|---|---|---|
| W | on the ITF | 0.044 | 0 | 1.08 |
| on the pickoff | 0.272 | 0 | 0.180 | |
| N | on the ITF | 0.040 | 0.18 | 0.72 |
| on the pickoff | 0.247 | 0.029 | 0.118 |
