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Environmental Monitoring (Environmental Monitoring)
fiori, paoletti - 16:47 Tuesday 24 July 2018 (42197) Print this report
coherent 107Hz between RFC and magnetic probe at INJ small rack

This morning we placed one fluxgate probe at the small INJ rack located in the CEB entrance. The probe is just lying on the top of the rack.

We find good coherence at 107Hz and harmonics with RFC error signal (Figure 1). Indeed common peaks are seen in the spectra and spectrograms (Figure 2)

There is also large coherence on other spectral features mainly around 50Hz and harmonics (Figure 3, 4, 5).

Lets remind that the 107Hz peak is present in Hrec since long time (41824, 41812, 37744).

We should investigate more to try to understand the source and (possibly) the path: we suspect the source of the peak to be inside this rack or in its close proximity, we should try to move the probe around and check if and how the peak amplitude changes, possibly a selective switch off would be of help.

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fiori, paoletti, genin - 16:20 Wednesday 25 July 2018 (42212) Print this report

This morning we continued the investigation of the 107Hz noise:

we moved the magnetic probe in various positions in the rack. We found a large emission of 15.3 Hz and multiples (which include the 107Hz)  from the top picomotor drivers crate ("New Focus" brand). A similar emission was sensed placing the probe on the picomotor wires that leave the rack toward the INJ tower. These picomotors are only seldomly used for  beam steering and mode matching adjustments. There is a second picomotor drivers crate at the bottom of the  rack (same brand) which drives a translation stage on SIB1, also seldomly used. The mag emission from this second crate show no peaks but instead a large white noise.

We switched  both crates off and left them off. It will be good to have them plugged on a smart plug for the future. 

We observe a noise improvement in SSFS signal (the ITF was locked in low noise 3 at that time but DARM was too noisy). As shown in Figure 1, some peaks disappear, the most prominent is the 107Hz. (Figures 2 to 6). Also the 53Hz line (also 106Hz and159Hz) in SSFS that are associated to the temporary power generator (41386) decreased in amplitude.

We can notice (Figures 2, to 6) that RFC signal remains polluted by significant magnetic coherent noise all around 50Hz and harmonics.

 

side note: when placing theprobe close to the PC in the rack we measured significant emission at 23.9 Hz and multiples (47.8Hz, 71.7Hz, 143.4Hz).

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