The goal of the shift was to investigate the ITF behavior by moving the CO2 actuators on the ITMs.
As suggested by the commissioning coordinator, after the work performed on the ITMs/YAG alignment of the past days (58580, 58595, 58611), we started by investigating the vertical direction, moving separately the NI DAS first and the WI DAS after. Here are the details:
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15:27 UTC: CARM NULL 1F
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17.07 UTC: STEP (1) NI CO2 actuators moved by 5 mm along vertical direction (TX) upward (backward)
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19.23 UTC: STEP (2) WI CO2 actuators moved by 5 mm along vertical direction (TX) upward (backward)
We observed that (Fig.1):
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B7 and B8 started to separate in between STEP (1) and (2)
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12 MHz have bumps corresponding to the STEPs done and then stabilized at a level slightly improved wrt the previous one; similar behavior for 112 MHz
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B1p raised a bit up, but the drift was already ongoing before doing STEP (1)
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A small improvement of sidebands/carrier overlap is visible on PosX, starting form STEP (1): 56MHzLSB raised up, together with CAR.
The plot in Fig. 2 shows the evolution of the main figures of merit from the controls point of view. Starting around 18.00 we can see a differential variation of the arms power that doesn't seem related to the TSC activity. Also during the whole lock the SRCL SET and the DCP seem to have a decreasing trend not correlated to the TCS activity. Regarding the sidebands and B1p DC it seems to be a small increase of the power at the same time as the movement of the TCS actuators. It is not clear the effect on the CMRF.
Overall, the impact of these actions is not very big.
We decided to leave the CO2 actuators in this last alignment position, to further investigate its effect on ITF signals.
At the end of the shift, at 21.46 UTC the CH flip mirrors were opened one per time to raise up the powers, to improve the lock acquisition (issues highlighted here 58631). The following table summarize the changes (bold):
CH [W] | INNER DAS [W] | OUTER DAS [W] | |
W | 0.082 → 0.089 | 0.141 | 1.92 |
N | 0.126 → 0.133 | 0.286 + 0.08 (cold lens) | 2.277+1.8 (cold lens) |
During the N CH power change, the ITF unlocked. We tried some unlucky attempts to relock and then Julia and Magazzu put the ITF in autorelock up to CARM NULL.