As agreed, we started today’s DAS tuning in LN2 (8:17 UTC).
The actions performed on TCS DAS outer rings are summarised in the table below.
SUMMARY TABLE
| STEP # | Starting time (UTC) | DAS outer ring power variation | DAS outer ring values [W] | |
| W | N | |||
| 1 | 08:19 | WI DAS OUT +10% | 1.79 → 1.97 | 3.1 |
| 2 | 09:07 | NI DAS OUT +10% | 1.97 | 3.1 → 3.41 |
| 3 | 09:55 | WI DAS OUT -10% | 1.97 → 1.79 | 3.41 |
| 4 | 11:18 | NI DAS OUT -20% | 1.79 | 3.41 → 2.73 |
| 5 | 13:17 | NI DAS OUT +10% | 1.79 | 2.73 → 3.1 |
| 6 | 14:49 | WI DAS OUT -10% | 1.79 → 1.61 | 3.1 |
| 7 | 16:13 | NI DAS OUT -10% | 1.61 | 3.1 → 2.8 |
| 8 | 17.16 | NI DAS OUT +10% | 1.61 | 2.8 → 3.1 |
| 9 | 18.34 | NI DAS OUT +10% | 1.61 | 3.1 → 3.41 |
The STEP 1 (WI OUTer ring +10%) seemed to cause a slight increase of the SBs and a deterioration of B1p, B1s and CMRF.
Due to this, we decided to try to act on the other arm, but the STEP 2 (NI OUTer ring +10%) led to SBs getting lower, while B1p and B1s don’t seem to be changed. Furthermore, we noticed that BNS range worse starting from STEP 1.
We agreed to revert STEP 1, to see the effect of only STEP 2, doing STEP 3 (WI DAS OUTer ring -10%). As a result, SBs continued to go down, while other figures of merit (B1p, B1s, BNS range) came back to this morning's values.
Since the SBs decrease seemed to be correlated with STEP 2, we tried to revert the action on N arm with STEP 4 (NI Outer ring -20%). B1p and B1s remain untouched, while SBs and BNS range get better and then worse.
Before making any other change, we agreed to try an unlock and repeat lock acquisition.
12.03 UTC ITF unlocked.
12.42 UTC ITF locked in LN2.
Since we would like to understand if some other trend was going on in the meanwhile, we made STEP 5 (NI OUTer ring +10%) to restore the thermal actuation condition of this morning.
After around 1h and half we noticed that all the figures of merit almost reset the values to the one of this morning, except for SBs: after some investigations, Maddalena noticed that it could be related to Etalon loops (see Figure 1: behaviour of SBs level VS WI/NI temperatures from monday, as reference; the SBs level minima are reached, at different moments, between 10 and 14 UTC in the past days).
With STEP 6 (WI OUTer ring -10%) we start to explore the last direction left with the WI DAS. The effect was quite evident on SBs and also on B1p and B1s, all getting better.
Since B1p and B1s get slightly better but SBs lower dramatically, and the BNS range as well, we agreed to perform another step, the STEP 7 (NI OUTer ring -10%), to recover the SBs keeping the lower achieved values of B1p and B1s.
STEP 8 (NI DAS OUTer ring +10%) and STEP 9 (NI DAS OUTer ring +10%) were performed because the previous direction does not seem to be the right one. After these two steps, BNS range recovered, SBs improved and other figures of merit remained pretty stable.
Michal noticed that the MICH control loop was not working properly and corrected it manually just before letting the ITF go in LN3_ALIGNED (locked in this state at 19.50 UTC), in order to start the ENV low-noise injections.
In Figure 2 the general behaviour of the main signal during all the steps performed and Figure 3 a zoom of the last hours are shown.
The thermal configuration left for the night is reported in the table below.
|
| Last nominal configuration (21/01/26, 20 UTC) | CH [W] | INNER DAS [W] | OUTER DAS [W] |
|---|---|---|---|---|
| W | on the ITF | 0.052 | 0.150 | 1.79 → 1.61 |
| on the pickoff | 0.324 | 0.025 | 0.291→ 0.262 | |
| N | on the ITF | 0.094 | 0.48 | 3.1 → 3.41 |
| on the pickoff | 0.577 | 0.078 | 0.499 → 0.549 |
