Virgo Logbook

AdV-COM (AdV commissioning (1st part) )

bonnand - 14:47 Tuesday 23 October 2018 (43238)

Drops in Hrec range

I tried to have a look at what is happening to h(t) when the horizon is dropping suddenly such as yesterday evening, see figure 1.

So I plotted h(t), figure 2 and 3, at a quiet moment (in purple) vs during a time when a drop occured (in blue), I was surprised to see that the increase of noise looked like more or less the mystery noise in f^-5/2. The slope of the noise looks a bit different in figure 3.

I am not sure this is really an increase of the mystery noise or not. Talking to Michal Was, he told me this could come from a glitch.

So I made a spectrogram of h(t) around the time of the drop, see figure 4, it indeed looks like a glitch to me but I am no expert in DetChar and glitches... it would be nice if someone from DetChar could have a deeper look at this.

Images attached to this report

43238_20181023143944_hrecspectroaround2018102300h25drop.png

Comments to this report:

robinet - 16:46 Tuesday 23 October 2018 (43240)

Yes this is a broad-band glitch as plotted in Fig. 1. It stands on top of low-frequency glitches resulting from scattered light (typical arches). The rate of scattered light glitches is currently very high. The occurence of horizon drops is also high. Could the seismic activity be a common cause?

Images attached to this comment

43240_20181023164601_v1lscdarmomicronmapq2122428956020.png

swinkels - 16:49 Tuesday 23 October 2018 (43241)

Attached figure shows that one of the 4 drum modes gets excited at the moment of the glitch, so this is likely something on the payloads as seen during O2. According to Yuta's identification, this should be the WI mirror.

Note that the old entry is from the time when we still had steel wires, and one explanation at the time was a wire slipping over the stand-off prisms, which should not happen for the monolithic suspensions. I do not see any obvious excitation of the violin modes.

Images attached to this comment