It appears that some maintenance work on Tuesday March 14 led to degradation with respect to narrow lines in H1 DARM. The attached inverse-noise-weight spectra compare 1210 hours of data from the start of O2 until early morning of March 14 with 242 hours since that time. Summary of substantial comb changes: The comb with 0.9999-Hz spacing nearly aligned with N + 0.25 Hz (N = 15-55) is stronger. There is a new comb with 0.999984-Hz spacing visible nearly aligned with N + 0.75 Hz (N = 41-71) There is a new comb with 1.0000-Hz spacing visible at N - 0.0006 Hz (N = 104-125) Much activity was reported in the alog for March 14, but what jumps out at me are two references to HWS work: here and here. Are there HWS cameras running during observing mode? I had thought those things were verboten in observing mode, given their propensity to make combs. Fig 1: 20-50 Hz comparison (before and after March 14 maintenance) Fig 2: 50-100 Hz (before and after March 14 maintenance) Fig 3: 100-150 Hz (before and after March 14 maintenance) Attachment has full set of comparison sub-bands up to 2000 Hz with both A-B and B-A orderings to make clear which lines are truly new or louder.
We didn't change any configuration of the HWS camera that day. All HWS cameras have been turned on since the beginning of O2 and have been hooked up to the external power supplies (alog30799) since O1. Since then I haven't heard any complains about HWS cameras making noises. HWS cameras ON has been a nominal configuration since the beginning of O2.
I was asked via e-mail if this problem might have started later in March with the replacement of the Harmonic Frequency Generator. but explicit comparisons of daily spectra below show conclusively that the N + 0.25 Hz and N + 0.75 Hz combs are not present before Tuesday maintenance ("March 14" ends at 6:00 a.m. CDT on March 14 in the FSCan dating convention), but are present individually on March 15, 16 and 17. The new N Hz comb reported above is too weak to show up well in a single day's measurement with 1800-second SFTs. I was also told via e-mail (and just saw Nutsinee's note above) that HWS systems are run routinely during observing mode and that no configuration changes were made on March 14 (although there are some new cables in place). So perhaps there is a different culprit among the March 14 activities. Fig 1: Zoom in of line at 28.25 Hz Fig 2: Zoom in of line at 38.25 Hz Fig 3: Zoom in of line at 88.75 Hz Fig 4: Zoom in of line at 98.75 Hz
Looking back at the aLOGs from the March 14th period, some possibilities of activities that may be related stick out: 1) PSL bullseye detector for jitter studies installed 2) ITMY OpLev power supply moved 3) New cables for GigE and camera installed 4) ETM OpLevs laser power increased 5) CPS electronics power cycled and board reseated on WBSC1 ITMY 6) DBB powered up and supposedly powered off;is it still on??Kiwamu says he is 99% sure the DBB is off
It looks like all three combs jump in magnetometers at EX and EY between 3/14 and 3/15, but don't have any notable presence in the CS magnetometers.
More clues: at EX, there was a recent change point in the combs (strength drop) between 2/28 and 3/1. At EY, there was one (also a strength drop) between 3/7 and 3/8. These are Fscan dates, covering 24 hours back from the morning when they were run-- in any case, it looks like two prior Tuesdays may be involved.
As a side note, the 1 Hz comb with 0.5 Hz offset mirrors the stated behavior in several channels, at least one magnetometer at EX and one at EY.