Reports until 12:05, Friday 16 September 2022
H1 PEM (ISC)
benjaminrobert.mannix@LIGO.ORG - posted 12:05, Friday 16 September 2022 (64999)
Investigating 75 and 95 Hz peaks that appear in EX Magnetometers and DARM

I looked into some peaks we've been seeing in both EX magnetometer and DARM, particularly the broad 95 Hz peak. I plotted the power spectrum of one magnetometer, DARM, and their coherence for four different times to try and narrow down when these appeared.

As was noted by Georgia in the comments of this alog the broad 95 Hz peak shifted at some point in August 2022 (seen in the green and brown lines). I'll also note the 75 Hz peak is present and at about 1 coherence at these times too.

Looking at a time when we were locked in May 2021 (blue line), we can see the the 95 Hz peak was in the magnetometer, but does not seem to appear in DARM (although there is a small bump in the coherence).

Finally, going back to O3 (red line) neither the 75 Hz nor the 95 Hz peaks are present. However, there is a narrow peak at about 83 Hz that has been present since O3.

Images attached to this report