Summary

Last weekend I used the offset-lock methof to measure the cavity length noise of the OMC.  I tried this with a single-bounce beam last fall, but the intensity noise from the IMC was too large and it contaminated the signal.  Here, with the carrier light from the full IFO, the intensity noise is low enough that a good measure of the displacement noise can be made, at least below 100Hz.  Here I describe how to offset-lock the OMC and how the cavity length noise is measured; also I make a projection of the OMC cavity noise contribution to DARM.  Noise due to OMC length fluctuations should be >10x below the DARM noise floor, except around the ISI resonances at ~1kHz.

This result is complementary to the cavity length noise measurement that Koji & I made by PDH locking the OMC with a single-bounce beam.  In comparison, this half-fringe (or "offset-locking") method is limited by intensity noise, but it's less invasive and can be performed entirely from the control room.  It might be useful for, e.g., estimating the OMC cavity noise during PEM injections or remeasuring the displacement noise after we install dampeners on the HAM6 ISI (still speculative). 

[Yet another method is estimating the displacement noise from the dither-locking error signal; Koji has done this in April and it agrees with the PDH result below 10Hz, but above 10Hz the dither error signal is limited by sensing noise.]

Offset locking the OMC

Here are the steps to lock the OMC on the half-fringe, while the full IFO is locked (and the DARM offset engaged).  This is essentially the same technique as I used last fall (and is halfway coded in the OMC guardian), which was itself a copy of what Zach did at LLO.

• First, sweep the OMC to find the carrier TEM00 mode.  Lock the OMC on the carrier with the OMC-LSC dither and record the average power.  For the measurements detailed below, the power into the IFO was 2.3W, the DARM offset was 3.7e-5 counts (~42pm), and the DCPD Sum was 20.43mA.  Engage the DARM boost (FM7) to reduce intensity noise.  The OMC should be aligned with the QPD loops for the entirety of the measurement.
• Unlock the OMC, turn off the input to the length servo, turn off the boost and integrator, and turn off the dither to PZT1.  Zero the OMC-LSC_SERVO gain.

The next steps adjust the OMC-LSC error signal path to set the offset locking at the half fringe point:

1. Turn off the input to DCPD_NORM_FILT, and set DCPD_NORM_FILT_OFFSET to be equal to the DCPD_SUM when the OMC is locked on the resonance (in my case, 20.43mA).  Now when the OMC is locked on the half-fringe the input to the dither demodulation should be 0.5.
2. Turn off the highpass (FM1) and bandpass (FM5) fitlers on the input to the demodulation (this is the OMC-LSC_PD_IN filter module).
3. Set the dither frequency to 0 Hz (normally it's 4100 Hz), and set the demod phase to 90deg (normally 0deg).  This will demdulate the DCPD_NORM signal at DC and pass the cosine term to the length servo.
4. Set the OMC-LSC_SERVO_OFFSET to be 1/2 the gain of the cosine demodulation, that is, OMC-LSC_SERVO_OFFSET = 0.5 * OMC-LSC_OSC_COSGAIN.
5. Turn on the length servo, turn on the integrator, and turn on the gain.  I wound up using a very small gain, 0.01 gave a UGF of ~8Hz.  You may have to try this a couple of times, since there is a sign ambiguity that depends on which side of the fringe you're on.
6. Once you're locked, check that DCPD_SUM is 1/2 of what you measured on the full-fringe lock.  I had to adjust the length offset (step 4) to get true half-fringe locking.  Not sure why.
7. Measure the intensity noise on the OMC transmitted light (you can use DCPD-NORM_OUT_DQ), take an OLTF so you can correct for the loop suppression, and you're done.  Use the SDF table to undo all your filter changes.

Measurement of OMC Cavity Length Noise

Figure 1 illustrates how the offset locking technique uses the RIN on transmission to measure the cavity length noise (delta-x).  There's a theorist on my thesis committee, this is for them.

Figure 2 is the transfer function of the length servo, while locked on the half-fringe.  This was used to correct for the loop suppression.

Figure 3: the top panel is a plot of the measured RIN during the half-fringe lock (red), and the same data corrected for the loop suppression (blue).  The RIN has a noise floor of ~1e-7 / rt[Hz] above 100Hz.  This noise is coherent between the DCPDs and is well above the shot noise + dark noise level.  (To demonstrate this I plot the NULL stream, along with the DCPD dark noise; both of these were convereted to RIN-equivalent noise by dividing by the DCPD_SUM during the offset lock, 10.2mA.  The shot-noise RIN for 10.2mA is in good agreement with the NULL channel.)

I think the noise floor is due to intensity noise coming from the IFO, and above 100Hz we are not measuring RIN due to cavity length fluctuations (except around 1kHz, more on this later).  This 1e-7/rt[Hz] noise floor matches the noise floor of the ISS 2nd loop PDs (not plotted), but the coherence is not =1 everywhere.  Why isn't it filtered by the IFO?

Figure 4 is the cavity length noise derived from the RIN measurement, red is the in-loop data, blue is the 'free-running' length noise (corrected for loop suppression).  The displacement noise is calculated from the RIN using the RIN/dx relationship, derived from the cavity transmission formula.  For the OMC, locked halfway up the fringe, the conversion is 2.72e-9 meters/RIN - to get this number you need to know the transmissivity of the OMC input and output mirrors, it is 8000ppm.

Figure 5 is a comparison between our measurements of the OMC displacement noise: Zach's measurement from L1 (red); Koji's result from the PDH lock of the OMC (black); and this measurement (blue).  This plot is an update of LHO:16174.  In general the measurements are in agreement.  The PDH result has a lower noise floor above 100Hz; probably the other measurements are limited by intensity noise.  The half-fringe result is lower than the others around 10Hz; Koji measured the noise from the PZT drivers in January, this may be the limiting noise source for the current measurement.  (Zach says that the L1 measurement is possibly limited by laser frequency noise in the 3-40Hz band.)  The peaky excess in the half-fringe result around 1Hz and 3Hz are coherent with intensity noise and are not real cavity motion, see Fig. 3.

Figure 6 is a zoom of the region around 1kHz.

Projection to DARM_ERR

Here I estimate the contribution of OMC cavity length noise to the DARM noise.  Valera, Ryan, and Sam discussed this in G1100903, and I think my methods are essentially the same as what they describe.

First, the noise in the light transmitted through the OMC due to the (suppressed) cavity length noise can be calculated two ways:

1. by modeling the quadratic coupling of length noise --> DCPD_SUM when locked on the full resonance
2. by modeling a bilinear coupling between the RMS cavity offset and the length noise.

For the quadratic case, we calculate the noise in the power measured by the DCPDs due to the cavity length noise as:

dP[f] = (4*F/lambda)^2 * ASD[x(t)**2]

...where F is the cavity finesse (=391), lambda is 1064nm, and the final term is the ASD of the square of the cavity length noise, x(t).  This is a quadratic approximation to the peak of the Fabry-Perot transmission curve, for the OMC it is accurate for motion less than ~3e-11 meters, which is true for our data across all frequencies.  [Important: you have to take the ASD of the square of the time-series, not the square of the ASD -- the Fourier transform is a linear operator but squaring is not.  Thanks Sheila!]

Alternatively, the bilinear coupling is estimated as:

dP[f] = (4*F/lambda)^2 * 2 * x_rms * ASD[x(t)]

I've used x_rms = 3e-13 meters, although this could be an overestimate (see comment below).

Next, to convert dP[f] into an estimate for the DARM noise budget, I turn the crank on the DCPD_SUM --> OMC-READOUT_ERR calculation that is described here:

OMC-READOUT_ERR = DCPD_SUM * (Pref / P0) * xf**2 / (2*x0) * G

...where Pref = 1.56 (power normalization), P0 = 24.1 (input power, Watts), xf = 14 (fringe offset, picometers), x0 = 15.8 (DARM offset, picometers), and G = 8.56e-7 (overall gain factor).  These are the values during the lock on Jun 7 at 00:00 UTC that Evan used for his latest noise budget.  This calculation converts DCPD_SUM in mA into counts at the DARM_IN1 error point.

Finally, to convert counts of DARM_IN1 into meters of CAL-DELTAL displacement noise, I use a factor of 5e-7, a zero at 389Hz and a pole at 7kHz.  The factor of 5e-7 was estimated by matching DARM_IN1 to CAL-DELTAL_EXTERNAL_DQ in DTT.  This is about 3x larger than what I expected, based on the calibration of the DARM offset in counts to picometers: 1e-5 counts / 14 picometers.  Not sure why there is this discrepancy.

In Figure 7 I plot the CAL-DELTAL spectrum from June 7 with estimates of the contribution from the OMC, using the quadratic and bilinear coupling results.  As mentioned before, the OMC length noise projection above 10Hz is probably limited by intensity noise and is bogus, except for the peaks around 1kHz, which are about a factor of two below the noise floor.  If this result is correct, it's an ongoing mystery as to why we don't see this 1kHz noise in the DARM spectrum.  Robert has investigated the acoustic coupling in this band and also projects that some noise at ~900Hz should be peaking above the noise floor.  Why don't we see it?

For interested NoiseBudgeters, the attached text files have the data for the red (quadratic) and blue (bilinear) traces in Fig. 7.  (You shouldn't think this noise source has gone unattended in the noise budget until now: Evan says he had measured the OMC-->DARM noise coupling some time ago, using excitations into the OMC-LSC loop, and had convinced himself the OMC wasn't a source of broadband noise.  No reason to think any different from this study.)

(Betsy, Calum, Kate, Gary, Travis, Danny)

Since all other work at End-Y finished yesterday, today we performed the in-chamber SUS/SYS discharge procedure T150101 on ETMy and then closed the chamber. 

Todays sequence of events at EY:

Jim unlocked the ISI.

Filiberto checked for grounding of the TMS QPD cables at the feedthru since Keita/crew had made adjustments to them.  As well, we then rechecked the QPDs with a flashlight for response.  All is well with the QPDs post the strain relieving.

Locked lower masses of ETMy and installed discharge equipment onto QUAD frame.  Discharged ETMy.  Removed equipment and unlocked lower masses.  Numbers to follow regarding the charge measured at the ETMy before executing the procedure and after completed.  The procedure took about an hour.

Swapped in fresh 1" optic and 3" wafer contam. control witness samples - 1 each on the floor of the chamber just under the QUAD and the other set on the QUAD.  All in the same places as before.

Wiped the floor on the way out.

Measured ETMy main and reaction chain P, V, and L TFs.  All looked healthy with purge air on and soft cover over door.

Door put on, purge valved off.

Measured particle counts a few times throughout above.  Numbers to follow.

Summary: A seismometer was buried 40 m from EY to take advantage of strong attenuation of the tilt signal relative to the acceleration signal from distant sources. Seismometers located outside the buildings may be useful in reducing problems associated with tilt.

Our buildings are tilted by wind. Our seismometers do not discriminate between this tilt and acceleration (like a pendulum), so wind-induced tilt produces spurious control signals that can make it difficult to lock and maintain lock. A tilt sensor can be used to discriminate between tilt and acceleration, but we may also be able to discriminate between the two by taking advantage of source differences in the band below 0.5 Hz, where tilt generates the largest spurious acceleration signals. The tilt in this band is mainly generated locally by the wind pressure against the walls, while the acceleration signal is mainly generated by ocean waves and other distant sources.

While the seismometers are in the far field for most low frequency accelerations, they are in the near field for building-generated tilt (wavelengths at 0.1 Hz are about 50 km). To take advantage of the rapid attenuation with distance in the near-field, I buried an STS-2 seismometer in a meter deep hole I dug 40 m from EY (Figure 1).  Figures 2 and 3 show a comparison of the buried seismometer to the SEI seismometer on the ground inside the EY station. During the low wind period the spectra look virtually identical below 0.5 Hz and the coherence is high because the sources are mostly distant and the wavelengths are large. During the high wind period, the buried seismometer doesn’t change that much (there is some change in the microseismic peak because high/low wind were about 24 hours apart), but the building seismometer shows a huge signal from tilt.  The coherence in windy conditions is low because the tilt is highly attenuated 40 m from the building. Figure 4 shows spectra for higher wind, 15-35 MPH.

Of course the external seismometer would not detect real building accelerations due to the wind. But if the unwanted tilt signal dominates over the wanted wind acceleration signal, a seismometer outside the building may be useful, and I think that this is the case below about 0.5 Hz.

I note that I first tried this in the beam tube enclosure tens of meters from EY, but found that the wind tilts the beam tube enclosure almost as much as the building (but not coherently), supporting a hypothesis that aspect ratio is the important variable. Also, Jeff points out that, if we insulate the buried seismometer well (and I did not) we might even be able to do better than the building seismometers with their current insulation during even low-wind periods. Figure 5 is like Figure 2 except that the signal from the stage 1 Trilliums is included.

I set up an accelerometer on the beam tube and measured the accelerations as I simulated the tapping that I observed during cleaning, and my tapping experiment mentioned here: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=19038. Examination of the time series indicated that accelerations during typical taps reached about 1 m/s^2.  I suspect that some taps reached 1g. The figure shows spectra for metal vs. fist taps. The above link notes that I was unable to produce glitches while hitting the beam tube with my fist. The fist and metal taps both had about the same maximum acceleration of 1 m/s^2 (ambient acceleration levels are about 4 orders of magnitude lower), so the source of the difference in liberating the particles is probably not acceleration. Instead, it may be the change in curvature of the beam tube, which would be expected to be greater at higher frequencies. The responses from metal taps in figure 1 peak at about 1000 Hz while the fist taps peak at about 100 Hz. These results are consistent with a hypothesis that the metal oxide particles are liberated by fracture associated with changes in curvature rather than simple vertical acceleration.

When I was producing glitches in DARM for the link above, I noticed that we did not get glitches every metal tap but every several metal taps. I tried to quantify this by making many individual taps at several locations along the beam tube. Unfortunately, we lost lock with the first loud glitch and I did not get a chance to repeat this before the vent. Nevertheless, it would be good for DetChar to look for smaller glitches at the time of the taps given below. Allow a 1 second window centered around the times given below for my tap timing uncertainty. I tapped once every ten seconds, starting at ten seconds after the top of the minute so that there were six taps per minute.

UTC times, all on June 14

Location Y-1-8

20:37 - 20:38 every ten seconds

20:47 - 20:50 every ten seconds

Next to EY

20:55 - every ten seconds until loss of lock at 20:56:10

Here I present some results from our first Pcal sweep measurement (alog 19128 and 19132) in 5-5000 Hz frequency range.

The main conclusions are:

• Pcal showed an OK agreement in terms of a DARM optical response with our model (i.e. the one used for generating GDS and CAL-CS).
• Roughly speaking, Pcal agreed with our model with descrepancy of 20 % level in magnitude above 10 Hz.
  • Pcal X seemed to have a larger systematic of 20-ish% in the overall scale factor. Not sure why. Needs to repeat the measurement.
  • Pcal Y agrees with the model with several % at one time.
• The measured phase agree with the model within +/- 10 deg uncertainty below 1 kHz.
• Another sweep measurement on a different lock stretch showed a 20 % reduction in the optical gain.
  • presumably due to a different DARM offset and maybe different alignment (see alog 19014).
• For some reason, the measured magnitude descreases as it goes to lower frequencies below 10 Hz.
  • This somehow does not change the phase. I don't understand.

-----

This time, our traget was the sensing function or the DARM optical plant in counts/meters. To access the sensing function, we essentially need two different measurements i.e. a TF from ETM displacement to DARM_IN1 [cnts/meters] and DARM loop suppression [cnts/cnts]. Jeff took an open-loop TF and Pcal sweep for each arm, but unfortunately the Y arm measurement did not complete (alog 19128). Approximately 8 hours later of Jeff's measurements, TJ managed to measure a sweep of Pcal Y and DARM suppression TFs (alog 19132). So in total we have three different Pcal sweep data sets as follows,

• Pcal X sweep (13/6/2015 23:40:53 UTC)
• Pcal Y sweep (13/6/2015 23:56:21 UTC)
• Pcal Y sweep (14/6/2015 07:03:59 UTC)

The first two measurements were from a same lock stretch, and the last from a different lock stretch. All the measurement were made with a PSL requested power of 17 W. The plots below show the main results:

The first plot shows the estimated sensing functions from all three sweep measurements. As seen in the plot, signal-to-noise ratio becomes significantly low above a few kHz. Also as the sweep goes across the fundamental and the second harmonic of the violine modes, the coherence dropped and hence a low signal-to-noise ratio. The cyan solid curve represents the model that we have used for generating GDS and CAL-CS where the DC gain is set to 1.311x-6 cnts/meters and a cavity pole frequency to 355 Hz. Additionally, I set a delay time of the model to 55 usec by eye-ball fitting without any good explanation.

The second plot shows the residual between the measrured and model transfer functions. Even though the first two measurements were from the same lock stretch, they differed by approximately 20 % from each other. I am not sure what caused the descrepancy, but it is clear that the descrepancy is mostly in the scaling factor. The last measurement, which was from a different lock stretch showed a lower optical gain by 20 %. We know that our LSC automation can cause such a variation in the optical gain (alog 19014). So I believe that this 20% reduction is real and not due to some calibration in Pcal. Also the first and third measurements showed significant drop in the magnitude below 10 Hz by more than 50 %. Since the phase does not seem to roatte below 10 Hz, this is not a simple zero-pole argument. Looking at the Pcal active intensity stablization servos, Darkhan and I cofirmed that there was no saturation when the low frequencies were measured (although Pcal Y seemed to have saturated at the beginning of the measurement, meaning higher frequencies). We have no idea.

The analysis code, measurements and figures can be found in:

• aligocalibration/trunk/Runs/ER7/H1/Scripts/PCAL_TRENDS/2015-06-13_optgain_estimation.ipynb
• aligocalibration/trunk/Runs/ER7/H1/Results/PCAL_TRENDS/ *png
• aligocalibration/trunk/Runs/ER7/H1/Measurements/PCAL_TRENDS/ * txt

[sus crew]

Following the in chamber work from today at end-Y we took quick TFs on the quad and the transmon. They look ok.

Since the pump won't happen before tomorrow I started matlab tfs for all DOF.

The measurement will be running for few hours. 

Kyle -> Soft-closed GV7 and GV5 -> Vented HAM6 

Bubba, Hugh, Jim W. -> Removed HAM6 South and East doors 

Kyle, Gerardo -> Installed NEG and TMDS reducer nipple+valve+elbow at X-end 

Danny S., Gary T., Gerardo, Kyle -> Hung North door on BSC10 

(NOTE: Noticed ~1 hour before hanging door on BSC10 that the purge-air drying tower had been left off since tying-in the 1" TMDS line on Monday afternoon -> Turned it back on and notified the ETMY discharge crew

To test the power-up status of the SUS HWWD, I activated the SUS ITMY HWWD which is located in the CER SUS-C6 rack. The long DB-37 cables which run from the ITMY M0 OSEMS were not connected to the monitor ports of the HWWD. I found the cables on the top of the rack, and after verifying they were connected to the monitor ports of the satellite amps for ITMY M0 (located in the LVEA beer garden) I plugged them into the HWWD.

After the tests were completed, I disconnected the cables in the CER and returned them to the top of the rack.

Scott L. Ed P.

6/15/15
Cleaned 33 meters ending at HNW-4-076. Removed lights and move to next section north. Test results posted here.

6/16/15
Rehang lights, vacuum support tubes, spray heavily soiled floor areas with water/bleach solution and begin cleaning beam tube. Cleaned 19 meters ending at HNW-4-077.

6/17/15
Cleaned 60.6 meters ending at HNW-4-080.

A total of 3603 meters of tube have been cleaned to date.

Hugh, Bubba, Andres, Jeff B.

   After removing the HAM6 south & east doors, we rolled two cleanrooms and a garb room around the south and east sides of the HAM5/6 big cleanroom. The fans are on. There will be a cleaning of these cleanrooms in the morning. 

NOTE: The south corridor from just before HAM5 to the north side of the HAM5/6 big cleanroom is blocked. Access to the north side of the output arm will be from the long way around.    

Will run the Aux cleanrroms overnight before using.  Thxs to Andrias Jim Bubba JeffB

Dan Hoak gave us a clue on page 19067 and then Bas Swinkels ran Excavator and found that the channel H1:SUS-OMC_M1_DAMP_L_IN1_DQ had the highest correlation with the fringes. Andy Lundgren pointed me to equation 3 from “Noise from scattered light in Virgo's second science run data” which predicts the fringe frequency from a moving scatterer as f_fringe = 2*v_sc/lambda. Using the time from Dan and the channel from excavator and the fringe prediction, I wrote the attached m-file. Fig 1 shows the motion, velocity, and predicted frequency from OMC M1 longitudinal. Figure 2 shows the predicted frequency overlayed with the fringes in DELTAL. Math works.

PS. Thanks to Jeff and the SUS team for calibrating these channels and letting me know they are in um. Thanks to Gabriele for pointing out an error in an earlier draft of the derivative calculation.

Calibration Team

Sign of h(t):

The gravitational wave strain h(t) is given by  h(t) = Delta L/L where Delta L  is is computed using

                         Delta L = ± (Lx - Ly)

The sign of Delta L can be determined using Pcal actuation on the test mass. Pcal only introduces a push force  so pcal readout signal (truly pcal excitation) is minimum when the testmass is away from the corner station (closer to pcal laser). From the first plot the phase between DARM/PCAL is ~ -180 degrees (DARM lags PCAL) which suggests that DARM signal from ETMX will be maximum when pcal is minimum (ETMX further away from corner station). Similarly, from second plot, since DARM and PCAL have a phase difference of ~-360 degrees (essentially 0 degrees), the  DARM signal from ETMY is minimum when the pcal is minimum. This shows that the sign convention for the Delta L is '+'

Time Delay between Pcal and DARM:

Also the slope of the curve gives the time delay between Pcal and DARM signal chain. The time delay is about 125±20 us. This time delay can be accounted for, within the uncertainity, from the difference in signal readout chain outlined in Figure 3 attached.

Refer to LLO alog #18406 for the detailed explanation behind this  conclusion.

I modified and restarted the BSC-ISI models to close ECR E1500245, E1500253 and E1500270. The changes are listed below, and described in details in the attached pdf.

* removed sts blrms calculation from the sensor correction of stage 1. The calculation is now done at the top level. A list of the new channel names is provided in the attached text files 

* Added a pick off of stage 1 CPS X and Y signals to feed the LSC model through PCIE senders on BS ITMX and ITMY

* Added a path from sus to the error point of the stage 1 controls to use for tidal feedback (mainly for LLO). 

Corey, Keita, Kiwamu,

We conituned working on the remaining tasks for the TMSX in chamber (see alog 19157 from yesterday).

[Strain Relief for QPDs]

This morning we installed the strain reliefs for the two QPDs in which we had a difficulty inserting a screw due to bad threading. Today, we brought 10-32 screws so that the screw can go all the way through to the back without any interference from the bad threads. We put combination of a nut and washer on the other side to hold the 10-32 screw and the strain relief parts. We did this on the two QPDs. So now all four QPDs have the strain reflef parts installed.

[Balancing of the table]

We then balanced the table such that the green light is retro-reflected off of ETMY. The table seemed to have pitched by some amount. We decided to move the counter mass at the bottom of the table. The adjustement went very smooth and we were able to get the beam retrao-reflected all the way back to the PD on the ISCTEX table. Touching the TMS digital bias suggested that the pitch angle is good with a precision of about 4 urad. While pitch is good, yaw seemed to be slightly off. So we moved the digital bias in yaw as well and confirmed that adding an additional +40 urad (resulting in a bias of ) in the digital bias can give us a decent alignment on the reflection PD. So we are good in yaw too.

[Addendum]

After initial balancing we were concerned that we did not use vented washers for the two QPDs which required the screw/nut workaround.  Keita found that one QPD did NOT have a vented washer, so a vented washer was installed.  This required a re-balance.  We were a little off in pitch, so a counterweight (1/4-20 screw) was added to pitch the TMS.

Photos of this work from Mon afternoon & Tues morning is on ResourceSpace here.

EX is now Laser Safe.

(And ready for the SUS crew to take over.)

(times in PST)

0:04 - Locked @ LSC_FF, started PCAL swept line measurement

0:29 - PCAL measurment done, started DARM OLGTF measurement

0:50 - Both measurements done and no more for now it seems, Intention Bit set to Undisturbed

There were eight separate locks during this shift, with typical inspiral ranges of 60 - 70 Mpc. Total observation time was 28.2 hours, with the longest continuous stretch 06:15 - 20:00 UTC on June 11. Lock losses were typically deliberate or due to maintenance activities.

The following features were investigated:

1 – Very loud (SNR > 200) glitches
Omicron picks up roughly 5-10 of these per day, coinciding with drops in range to 10 - 30 Mpc. They were not caught by Hveto and appear to all have a common origin due to their characteristic OmegaScan appearance and PCAT classification. Peak frequencies vary typically between 100 - 300 Hz (some up to 1 kHz), but two lines at 183.5 and 225.34 Hz are particularly strong. These glitches were previously thought to be due to beam tube cleaning, and this is supported by the coincidence of cleaning activities and glitches on June 11 at 16:30 UTC. However, they are also occurring in the middle of the night, when there should be no beam cleaning going on. Tentative conclusion: they all have a common origin that is somehow exacerbated by the cleaning team's activities.

2 – Quasi-periodic 60 Hz glitch every 75 min
Omicron picks up an SNR ~ 20 - 30 glitch at 60Hz which seems to happen periodically every 70 - 80 min. Hveto finds that SUS-ETMY_L2_WIT_L_DQ is an extremely efficient (use percentage 80-100%) veto, and that SUS-ETMY_L2_WIT_P_DQ and PEM-EY-MAG-EBAY-SEIRACK-X_DQ are also correlated. This effect is discussed in an alog post from June 6 (link): "the end-Y magnetometers witness EM glitches once every 75 minutes VERY strongly and that these couple into DARM".  Due to their regular appearance, it should be possible to predict a good time to visit EY to search for a cause. Robert Schofield is investigating.

3 – Non-stationary noise at 20 - 30Hz
This is visible as a cluster of SNR 10 - 30 glitches at 20 - 30 Hz, which became denser on June 11 and started showing up as short vertical lines in the spectrograms as well. The glitches are not caught by Hveto. Interestingly, they were absent completely from the first lock stretch on June 10, from 00:00 – 05:00 UTC. Daniel Hoak has concluded that this is scattering noise, likely from alignment drives sent to OMC suspension, and plans to reduce the OMC alignment gain by a factor of two to stop this (link to alog).

4 – Broadband spectrogram lines at 310 and 340 Hz
A pair of lines at 310 and 340 Hz are visible in the normalized spectrograms, strongest at the beginning of a lock and decaying over a timescale of ~1 hr as the locked interferometer settles into the nominal alignment state. According to Robert Schofield, these are resonances of the optic support on the PSL periscope. The coupling to DARM changes as the alignment drifts in time (peaks decay beacuse the alignment was tuned to minimize the peaks when the IFO is settled.) Alogs about this: link, link, link.

There are lines of Omicron triggers at these frequencies too, which interestingly are weakest when the spectrogram lines are strongest (probably due to a 'whitening' effect that washes them out when the surrounding noise rises). Robert suspects that the glitches are produced by variations in alignment of the interferometer (changes in coupling to the interferometer making the peaks suddenly bigger or smaller).

5 – Wandering 430 Hz line
Visible in the spectrograms as a thin and noisy line, seen to wander slightly in Fscan. It weakened over the course of the long (14h) lock on June 11. Origin unknown.

6 – h(t) calibration
Especially noisy throughout the shift, with the ASD ratio showing unusually high variance. May be related to odd broadband behavior visible in the spectrogram. Jeff Kissel and calibration group report that nothing changed in the GDS calibration at this time. Cause unknown.

Attached PDF shows some relevant plots.

More details can be found at the DQ shift wiki page.