Virgo Logbook

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Detector Characterisation (Glitches)

swinkels, van beuzekom - 15:01 Friday 09 August 2019 (46627)

Payload glitch

While looking at some low-frequency glitches, we found a classic example of a payload glitch, see fig 1. These are events that must originate on the test mass payloads themselves, since they excite many of their resonances. In this case, the glitch was very loud: it was the loudest Omicron trigger of the day with an SNR of 2400 (and a frequency of 72 Hz, probably just the impulse response of the DARM loop), which excited violin modes up to the 9th harmonic and many of the known mirror modes, see fig 2. According to the identification of the drum modes by Yuta, the NI mirror was the culprit this time, see fig 3. More of these events might be found by looking for the signature of a ring-down in the amplitude of the drum modes, see fig 4. A quick search by hand did not show any similar events, so the very loud ones are probably very rare. This does not exclude the possibility that there are many similar events that are too weak to identify.

Images attached to this report

Comments to this report:

puppo - 19:40 Monday 26 August 2019 (46772)

Here it is a list of the NI modes and their Q measured from ring downs:
Freq tau(s) Q(1e6)
5721.5700 745.10 13.393
7805.2260 419.79 10.294
7993.4930 75.890 1.9058
8908.950 38.000 1.0636
8914.850 108.09 3.0273
9665.981 1079.5 32.781
9670.481 143.85 4.37
10101.06 7.7800 0.24689
12507.78 4.5300 0.17800
12547.40 5.8840 0.23194

the analysis is still in progress.
A first comment is that the Q values measured from ring down are very close to the measurements already presented from the Lorentzian widths.
All the mode shape are identified.
A further evaluation of the NI thermal will follow.