MORNING/AFTERNOON up to 19.35 LT
To verify the lock acquisition in the cold state of the ITF, we kept the interferometer unlocked for one hour.
Julia performed the unlock at 07:35 UTC.
The sideband behavior was monitored for one hour by repeatedly locking and unlocking the CITF. It was observed that the sideband level gradually decreased as the ITF cooled down (see figure 1).
After several steps increasing both WI and NI CH powers, we were able to recover some sideband power and proceed with the lock acquisition (see fig.2).
The new powers compared to the standard ones (pre WE mirror replacement) are summarized in the table below .
|
| Reference | CH [W] | INNER DAS [W] | OUTER DAS [W] |
|---|---|---|---|---|
| W | on the ITF | 0.046 → 0.057 | 0.150 | 1.596→2.1 |
| on the pickoff | 0.284→ 0.35 | 0.025 | 0.260→0.338 | |
| N | on the ITF | 0.104 → 0.113 | 0.340 | 3.77→4.2 |
| on the pickoff | 0.635→ 0.695 | 0.055 | 0.613→0.68 |
The ITF relocked at CARM NULL 1F at 10:24 UTC. However, the interferometer experienced multiple unlocks at different stages: one occurred at CARM NULL 1F (at 11.06 UTC) — shortly after I opened and closed the flip mirrors of the CO2 actuators to check the power individually — and two others took place during the LN2 acquisition phase (at 10.51 and 11.44 UTC).
With Michal, we understood that many unlocks during the night and throughout the day were caused by the saturation of B1s during the acquire Low Noise 3.
We hypothesized that the issue could be related to the last step of the NI outer ring, performed yesterday at 17:00 UTC.
As a result, this step was reverted in the CARM NULL 1F configuration at 13:19 UTC.
However, although the fringe became brighter, we tried to reach LN3 but the ITF unlocked due to a glitch in the BS.
The ITF relocked in CARM NULL 1F at 14:57 UTC, and at 14:59 UTC I increased the NI outer ring by 5%.
At 15:33 UTC, the WI outer ring was increased by 14% (from 0.36 W to 0.41 W on the pick-off).
Following this step, we observed an improvement in the 6 MHz. We then attempted to reach LN3, but the ITF unlocked during the acquire LN3 phase due to B1s exceeding the threshold of 42 (again).
Then we relocked at CARM NULL 1F and I increased the WI outer ring by 12% (from 0.41 W to 0.46 W on the pick-off) at 17.21 UTC.
The main signals to date are shown in fig.3.
