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AdV-DET (Commissioning)
genin, fiori - 11:01 Saturday 23 September 2017 (39564) Print this report
Comment to Investigations on OMC angular noise coupling and best SDB1 angular set points (39537)

Regarding the 270 Hz peak which seems to be present on DARM since the Laser room to SIB2 room door and cleanroom to SIB2 door have been opened. We can clearly see it on theĀ 

the Beam Pointing control system signals (see attached plot). We could not see any excess of accoustic noise at that frequency but there is a slight effect on the seismic noise measured with the accelerometer on top of the EIB which suggest that a resonance of a mount (maybe EIB_M6 one) could be excited (see entry https://logbook.virgo-gw.eu/virgo/?r=38640).

The strange thing is that the excess of noise read by the BPC quadrants is very small and we are not expecting any limitation from input beam jitter noise at that level when looking at the last noise projection we made on the 13th of september (https://logbook.virgo-gw.eu/virgo/?r=39459). At that time, we injected a large boradband noise without being able to see any coherence for frequencies higher than 100Hz.

Maybe this noise comes from the CB clean rooms and couple the ITF through PRCL (SIB2 PDs)?

We plan to make more investigations next week on that issue trying to understand it better and solve it.

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