The good: we now have access to longer segments of observing-quality data and can get a clearer look at narrow spectral artifacts. It looks like the line and comb situation is fairly stable and consistent with previous observations in smaller data sets. We're generally not seeing new problems arising, but are better understanding the existing problems and their scope.
The bad: Combs are more pervasive than previously known, especially at intermediate and high frequencies. In particular, a large number of spectral bins are contaminated by a set of ~9.47 Hz combs over a wide spectral range, which is problematic for CW searches.
The details:
The 4.98423 Hz comb is still present and clearly visible at low frequencies. The ~9.47 Hz combs (specifically 9.47431, 9.475383, and 9.480526 Hz) are weaker, but the larger data set reveals that they are more pervasive. They contaminate a spectral region spanning from about 200 Hz to 930 Hz (98th harmonic). There are 3 distinct combs involved in this structure; the triple peak can only be seen at high spectral resolution.
There is also a 29.969515 Hz comb which is visible up to its 60th harmonic at about 1800 Hz, and a 99.99864 Hz comb which is visible up to at least 2 kHz.
Coherence information:
We also have averaged coherence data over the same time period. As a reminder, Fscan tracks a limited set of high-priority channels and not the full DetChar list.
- Many of the combs (4.98 Hz, 9.47 Hz, and 29.97 Hz) are coherent across the CS magnetometer channels. They do not appear in the EX or EY magnetometers. This is consistent with previous observations.
- The 99.999 Hz comb is coherent with almost all the channels we’re tracking in Fscans including CS, EX, and EY magnetometers. It is also coherent with H1:CAL-PCALY_RX_PD_OUT_DQ. We do not understand why this comb appears in a PCAL channel.
- Previous studies led to us tracking H1:ASC-OMC_{A,B}_{PIT,YAW}_OUT_DQ with Fscans. Most of the observed combs are coherent with A_PIT, A_YAW, and B_PIT, but not with B_YAW. The 4.98 Hz comb alone is not seen by any of these four channels. It's not clear what is different about the 4.98 Hz comb, and what is different about the B_YAW channel.
Prior related alogs: 68261, 66925
Attached figures: (1) 200-930 Hz plot demonstrating the range of the 9.47 Hz combs, as well as some of the other noted combs. (2) Zoom on the triple peak of these combs. (3) Low frequency spectrum demonstrating the 4.98 Hz comb.
Carolina Li, Ansel Neunzert
Summary
It looks like the pervasive ~9.47 Hz combs are coherent with:
- H1:PEM-CS_ACC_PSL_PERISCOPE_X_DQ
- H1:IMC-WFS_B_Q_YAW_OUT_DQ
- H1:IMC-WFS_A_DC_YAW_OUT_DQ
- H1:PEM-CS_ACC_PSL_TABLE1_Y_DQ
Related to jitter?
(The WFS channels see the 29.97 Hz comb too.)
Background
For reasons of computational cost, Fscan only tracks a limited channel list-- not including these channels. However, daily bruco scans are generated through the STAMP-PEM monitor (thanks Kiet!) which are are lower resolution but cover many more channels. Carolina has been working to cross-reference the STAMP-PEM data with Fscan data to extract hints about promising channels for noise-hunting, working around the frequency resolution by leveraging the fact that combs show up in multiple spectral bins and should have the same coherences in all of them. Carolina generated a generated a heat map counting the number of times that various channels were coherent with h(t) in the STAMP-PEM frequency bins (low resolution) corresponding to Fscan auto-generated combs (high resolution). Fig 1 shows her initial test case, which clearly highlights the listed channels. This prompted me to follow up with higher-resolution Fscan spectra and confirm.
In parallel, Elenna had recommended taking a look at a wider set of channels related to jitter noise, which it just so happens these channels are part of...
Attached figures
1: heat map generated using STAMP-PEM coherence data and Fscan comb lists
2-5: high resolution Fscan coherence spectra for the channels listed, overlaid with Fscan comb lists
Attached data is for July 6.
