Given that H1 is still in commissioning mode, I hesitate to report on lines that may be due to ongoing work, but I'm seeing a very strong 1-Hz comb in DARM as of last Wednesday, which I suspect is unintended. Below are spectra of 20-120 Hz and its 20-Hz sub-bands from yesterday's data (typical of daily spectra since Wednesday). Note that the lines are on exact 1-Hz multiples (to ~0.5 mHz resolution), but they have flat shoulders of O(0.01 Hz) full width. An arbitrary but typical example at 34 Hz is shown. Also, the amplitudes of the lines do not fall entirely monotonically with frequency. There are clusters of lines with a spacing of roughly 7-8 Hz. Any ideas on what changed, perhaps during the last Tuesday maintenance?
Additional clue: there are small but noticeable changes in comb strength in a couple magnetometer channels at EX, in the same time frame. I'm not seeing anything similar in EY or CS mags. (The 1-Hz comb is present in many magnetometers; it's the change points that seems to be unique to EX.)
Hey all,
This looks similar to what we have seen in the past from the hartmann wavefront sensor cameras. It seems like we solved the issue by changing the camera power supplies. We can double check this by changing the HWS sync frequency at low noise and provide you with a gps time.
Sheila, Anamaria
The first thing that comes to mind from last Tuesday is a change to the ESD driver grounding at EX (47308), which did reduce some coherence between EX magnetometers and DARM (47323) At first it looked like this work last tuesday removed a line at 73 Hz from DARM, although looking at the summary page you can see that this line has been coming and going and was at 72.5 Hz yesterday. summary page
It's probably not the HWS because those were always showing up a few tenths of a percent below their sync frequency, so if this comb is within half a mHz it's too accurate.
Ok, I'm posting more detail on what I'm seeing in the magnetometers, in case it helps to pin this down. I've checked for any obvious/clear change points, and also compared whether the shape of the comb is similar to what's observed in DARM (same pattern of variation in peak heights). In summary, SEIRACK and SUSRACK magnetometers at EX are particularly notable.
Also, the comb does appear to be precisely on 1 Hz, unlike the HWS comb.
Detailed magnetometer report:
[Corner station]
H1:PEM-CS_MAG_EBAY_LSCRACK_*_DQ: no apparent change; comb shape dissimilar from what is observed in DARM
H1:PEM-CS_MAG_EBAY_SUSRACK_*_DQ: no apparent change; comb shape dissimilar
H1:PEM-CS_MAG_LVEA_VERTEX_*_DQ: comb not really present
[End X]
H1:PEM-EX_MAG_EBAY_SEIRACK_X_DQ: changed (decrease); comb shape similar
H1:PEM-EX_MAG_EBAY_SEIRACK_Y_DQ: no apparent change; comb shape similar
H1:PEM-EX_MAG_EBAY_SEIRACK_Z_DQ: changed (increase); comb shape similar (?)
H1:PEM-EX_MAG_EBAY_SUSRACK_X_DQ: changed (increase); comb shape similar
H1:PEM-EX_MAG_EBAY_SUSRACK_Y_DQ: no apparent change; comb shape similar
H1:PEM-EX_MAG_EBAY_SUSRACK_Z_DQ: changed (decrease); comb shape similar (?)
H1:PEM-EX_MAG_VEA_FLOOR_*_DQ: comb not really present, but neither is anything else. These channels look way too clean; there might be an issue.
[End Y]
H1:PEM-EY_MAG_EBAY_SEIRACK_*_DQ: no apparent change; comb shape similar
H1:PEM-EY_MAG_EBAY_SUSRACK_*_DQ: no apparent change; comb shape similar
H1:PEM-EY_MAG_VEA_FLOOR_*_DQ: no apparent change; comb shape similar (?)
Robert, Anamaria
Even with just 0.01 Hz resolution, there is large coherence between various magnetometers in the EBAYs and DARM. Indeed this was not the case before last Tuesday.
Separately, the 72.5 Hz that appeared in the last two days is coherent with the corner EBAY magnetometer in the ISC rack. We think it's a real peak because if the sensor were picking up DARM the large calibration lines at 35ish Hz would show better coherence. Though it does not appear to be there this morning, so not completely clear what's going on.
Danny and I had a 72.33 Hz line driving some frequency noise over the weekend during some TCS tests. We also had lines at 3.25kHz, 4.5kHz and a bunch around 23-25Hz.
Shifted ETMX HWS sync frequency from 1 Hz to 5 Hz starting at 1236485181 and shifting it back to 1 Hz at 1236494796.
What about the GPS clocks that got turned on last Tuesday?
I had trouble finding a lot of clean DARM data during the period when the HWS frequency was changed, but what I found suggested the 1-Hz was still strong. Figure 1 is from when the HWS frequency was normal. Figure is from when it was changed.
The 1 Hz comb is still present in data from the third week of ER14, see first attached plot. There is also a very bad 0.8 Hz comb visible between 420 and 500 Hz, see second plot.
The 0.8 Hz comb Pep noted is a complicated structure, but it has some symmetrical features which are centered on the 516.78 Hz line. Keith tells me this is an EX violin mode (alog 47650, alog 47179). A plot showing data from March 25 is attached.
It seems that the work reported in https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=47766 has made the 1 Hz comb disappear.
The first attached plot shows the spectra before this change, and the second one the spectra after this change.
On the other side, the lines and 0.8 Hz comb around the ~500 Hz violin modes are still there.
