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AdV-TCS (CO2 laser projector)
bersanetti, lumaca, mantovani, nardecchia, ruggi, spinicelli, was - 22:08 Wednesday 22 October 2025 (68015) Print this report
TCS CO2 tuning

After the tuning of yesterday evening (68010), this morning the ITF successfully locked in LN3.
Together with Michal, it was decided to slightly increase the PR CHRoCC driving voltage in order to recover the previous heater operating temperature of 136.5 °C, which had drifted downward over the past two days.
At 06:50 UTC, the voltage applied to the PR CHRoCC was increased (4.14 V → 4.16 V).
An unlock occurred about six minutes later, but it was possible to relock again in LN3 soon after.

Since no significant impact was visible from the PR CHRoCC, we decided to act on TCS CO2 actuators, starting from WI, that showed the issue yesterday.

We performed the following steps:

Step 1 (10.21 UTC) WI DAS IN & OUT +10% 

  •  WI CO2 PICKOFF = 0.30 → 0.303 (inner +10%) → 0.33 (outer +10%)

Step 2 (11.59 UTC) WI DAS IN & OUT +10% WI DAS 

  • WI CO2 PICKOFF = 0.33 W → 0.333 W (inner +10%) → 0.363 W (outer +10%)

Step 3 (13.30 UTC) NI DAS IN reverse of yesterday’s step

  • NI CO2 PICKOFF = 0.633 W → 0.57 W (inner *½)

Step 4 (13.42 UTC) NI DAS IN 

  • NI CO2 PICKOFF =  0.57 W → 0.633 W (inner *2)

Step 5 (14.39 UTC)  NI DAS OUT +20% (to recover the Dioptres variation due to WI steps)

  • NI CO2 PICKOFF = 0.63 W → 0.73 W (outer +20%)

The first two steps raise the SBs and improved their balance. After the second step, the MICH SET started to reduce but B1p got higher. See Fig. 1

To recover B1p, we first tried to revert the step performed yesterday evening with the NI IN (Step 3), but the negative effect was visible pretty soon in SBs and their balance; the effect on B1p was really low, so we reverted it. See Fig. 2.

We finally decided to make a fifth step, raising the NI OUT by the amount required to produce on the NI the same diopter variation obtained on the WI during the first two steps. The ITF unlocked almost 30 minutes later, not allowing us to look at the steady state. 

Since the ITF doesn't manage to go further than CARM NULL 1f for several times, we decided to roughly adjust the CHs powers to recover SBs level (17.00 - 17.45 UTC). 

This action, together with some SR misalignment (around 2 urad), allowed it to reach LN3 at 19.31 UTC.

 

We agreed to leave as it is for the night and set SCIENCE mode.

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casanueva, lumaca, mantovani, nardecchia, was - 15:44 Thursday 23 October 2025 (68021) Print this report

This morning we performed a single DAS tuning step (STEP 6).

In the current configuration, the NI inner ring power had to be set much higher than in previous weeks, which is unusually large with respect to the typical working point.

To move back towards a more standard configuration, we decreased the NI inner ring power and increased the WI inner loop power by about 10%.

-Increase the WI inner ring power  by about 10%.

-Decrease the NI Inner ring power by about 10%.

Step completed at 06.40 UTC.

Unfortunately, once again we observed a drastic degradation of the sidebands (see attached figure).

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