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AdV-ISC (Commissioning up to first full interferometer lock)
casanueva, pinto, tringali, fiori, spinicelli, derossi - 17:15 Friday 16 April 2021 (51444) Print this report
ALS/ISC shift: noise investigation

Today's task was to perform a noise investigation planned together with the ALS team.
From the beginning of the shift we experienced some problems when we were trying to lock the green on reallocation, both for the West and for the North in particular, which showed a lot of low frequency oscillation well visible on the and NEB_PD_GREEN_DC signals.
After a while the West locked quite reliably, while the North was still showing the same problems. At first, to make the system more stable, we worked on the triggers for north arms reducing their values on the ALS_NARM.ini scripts; then we improved the alignment of the North working with the Galvos. Nothing seemed to solve the problem, as the North arm was still keep unlocking, showing the same oscillations.
Then we discovered that the problem was related to the SNEB Local Control. In figure 1 is reported the trend of the SNEB_LC_TX/TY/TZ and SWEB_LC_TX/TY/TZ signals of the past two days, for comparison. As shown, starting from yesterday evening the motion of the SNEB, especially in the TY direction has increased considerably, with the respect to the SWEB values, which showed a pretty stable trend.

At 13.25.20 UTC, after a small intervention os R. Gouaty, we were able to lock the Green N/W in reallocation for about 30 minutes.

At the end of the shift we left the system to the crew of the afternoon shift, which will carry on the planned activity, considering that the oscillation are still present, even if smaller.

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