We managed to damp this bounce mode using the optical lever signal.  This has the advantage of not needing anything to be locked, so it is very robust, which is important since it took about 2 hours to damp.  The first image shows the L2_OLDAMP_P filter configuration we were using, and a time series of the resulting coil signal.  The second image is a trend of the OLDAMP_P_OUT signal, which shows the damping in action (the envelope of the signal slowly decreases with time as the mode rings down, and then jumps up each time we increase the gain).  After a couple of hours of damping, we were able to reduce the mode amplitude by a factor of 10, and then return to locking.  Note - the bounce mode frequency is 9.775 Hz

I want to give some more detail on the filters we used for the bounce mode damping:

We used the ETMX_L2_OLDAMP_P filter, and had only FM1 (0:0.5) and FM6 (Pass 9.8) engaged. The OLDAMP pitch gain was -1.

Jeff, Dan, Alexa, Evan, Matt

To illustrate the need-for / effect-of the feedback to HEPI from ALS_COMM, I attach two plots.

The first shows the start of an IR lock in the arms.  The ALS_DIFF path is turned on about 1/3rd of the way through.  Once the differential degree of freedom is out of the arms, the tidal drift begins to dominate the ALS green control signals, and the VCOs run away.  The rail at 7V in end-X is where we lose the lock.

The IMC control signals

In the second image, I plot a series of locks around the time when Nic implemented his ezca servo code.  After some missteps for gain tuning the offloading of the COMM signal to HEPIkeeps the VCO in range.

Nic's code uses MC_F, but for a permanent digital implementation we think that MC_L is a better choice.  The current plan is to add a PCIE channel to the LSC front-end module to send MC_L (the input of the LSC-MC filter) bank to the endstation HEPIs.

K. Venkateswara

It looks like you may have the sign of the sensor correction wrong. It looks like you are adding instead of subtracting the ground, hence the result looks a factor ~2 higher. Have you tried the opposite sign?

On the evening of the 19^th commissioners noticed large angular drifts on ETMX, see alog 15193. The attached plot shows temperature in end X over the past 3 days as well as the optical lever readouts. There is a clear correlation between temperature and optical lever readouts. The trace of the 0.8 C excursion on the 19^th in the optical levers is obfuscated by several re-alignments of ETMX. One might wonder, if the optical lever temperature fluctuations correspond to actual optical alignment changes, or if they are just an optical lever feature. Since large alignment drifts were reported on the 19^th, one might suspect the former.

Alignment changes of the order 0.5–1 µrad will require a re-alignment of the arm cavity.

Looking at a trend from 3 weeks ago shows that the temperature is now oscillating with a ~2.25 h period and an amplitude of ~0.15ºC.

Here is an LLO alog describing a measurement of the angular misalignment when their HVAC system was shut off. One can deduced a temperature dependency around 35 µrad/°C in pitch, see alog 13817. Yaw seems relatively stable. With a requirement of 0.5–1 µrad the temperature stability would need to be around 0.02ºC.

The other thing noteworthy is that it takes less than an hour for the vertical position to turn around after the HVAC system was engaged. This would indicate that the dominant thermal coupling is radiative through the chamber walls, and not conductively through the ISI. The reaction time of the ISI is of order 36 hours—which could be responsible for the long tail seen in restoring the position.

The calculation made by Brett in the above referenced link, as well as the measurements of pitch vs temperature that are reported by Stuart A in the LLO log, correspond to the pitch of the TOP mass of the quad suspension. According to the suspension model, the test mass pitch is 25% of the TOP mass pitch. So, the 30-40 urad/C for the TOP mass translates to 8-10 urad/C for the test mass. So 1 urad corresponds to 0.1 C. Still quite sensitive, but not so bad.

Not sure, if this still agrees with the observed optics drift. If I interpret the plot in alog 13639 correctly, the HVAC system was off for about 20 h, in which the temperature was rising by ~3.2 F. Assuming a linear trend we get 90 mK/h, or 15 mK in 10 minutes. The optics was drifting 0.5 µrad in 10 minutes. So, we get ~34 µrad/K at the optics.

On the other hand, looking at the temperature oscillations in EX we would expect to see 10 µrad-pp, but only see 1 µrad-pp. A time constant of ~1 hour would correspond to a pole frequency around 50 µHz which is abount 2.5 times slower than the observed oscillation. Assuming this leads to an attenuation of 8 dB, a reduction of 25% through the suspension chain would explain what we see in the optical lever.

ITMX Stage2 H2 & V1 CPS offsets are 900 & 3800 counts.  While V1 is actually the largest offset of all the BSC CPSs, H2 is 21st of 30 (towards the bottom) of Stage2 CPS offsets.  At 1200cts, BSC2 H2 ranks 17th of 30.  So the offset maybe an issue for ITMX V1 but the others...?  And, what about ITMY V1 at 3700 counts and ITMX V3 at 3200?

Attached are all the BSC medms showing the offsets.

Some additional info regarding the CPS - On the figures are plotted time series, integrated RMS, and  ASD down to low frequencies. Somme comments:

- At high frequencies, not much to add on sensor noise (ITMX and BS both have two CPS untis with elvevated sensor noise on Stage 2).  I looked at data of the Nov 17th, 18th and 19th, and get similar results.

- All Stage 1 CPS units are within 1um p2p, except BS horizontal that is moving 4 times more. Something to look into.

- At the microseism, the three vertical sensors are moving in sync, on all stages of all platforms. Probably normal  (the platform is inertially decoupled down to the micro-seism with th 90 mHz blends)

- The low frequency motion amplification is about 100 times larger in the vertical directions than it is in the horizontal directions.

The 5 figures in the previous log are for data ten on the 17th at 3pm PT. 

Results and comments are similar for the 18th and 19th, except for ETMX (attached plot) that shows different behavior at low frequencies, as expected with the sensor correction that was turned on Tuesday. It also shows features on Stage 2 at the SUS resonances, that might need to be doubled checks.

Could this be related to the trips on ITMX?  (alog 15021) 

this log seems to have gotten hijacked

I check the HAM-CPS and they all seem to be good at high frequency

Initially:

SR2 [2963.7, 2728.0]. SR3 [430.3, 142.6].

Centered AS_C using SR2 offset: [2917. 7, 2794.0].

At this point ASC_SUM was [1576.29, 1576.87] (measured twice, each is 10sec average number).

SR3 scan on SR2 peanut baffle:

Position 1: [3042.9, -438.4].

Position 2: [-2137.1, -408.0].

Center = (Pos1+Pos2)/2 = [452.9, -423.2].

Then moved the beam to the right edge.

Position 3: [452.9, -1248.4+-100]. Barely touching.

Position 4: [452.9, -1848.4+-500]. Totally blocked.

For whatever reason YAW is much more ambigous than PIT to my eyes, and right edge is more difficult than top and bottom.

Right = (pos3+pos4)/2 = [452.9, -1548.4+-510].

Center-Right = 1125.2+-510 in the slider counts. This is supposed to be 36.75mm.

SR3-SR2-SRM angle is 1.67deg, and the baffle-SR2 distance seems like about 46cm (eyeballing HAM4 systems drawing), so the beam distance at the baffle is 17.5mm.

New beam position = 17.5mm/2 =8.75mm to the left of the center.

Y=-423.2 + 8.75mm/36.75mm * (1125.2+-510) = -155.3 +- 120;

NEW SR3 slider = [452.9, -155.3+-120];

At this point SR2 was moved to [2708.7, 814.0] to center AS_C, and the SUM was found to be [1596.99, 1597.84, 1596.48] (three measurements), this is about 1.3% increase from the initial number (but note below about the interference pattern caused by either some etalon effeft of a ghost beam from somewhere).

SR2 scan on SRM/Faraday:

Scanned SR2 in YAW, then in PIT, to find the Faraday edge while centering AS_C using Pico.

Today I made a finer scan than previously done (https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=15023)  and what I originally thought to be a ghost beam looked more like an etalon type interference that mostly depend on the beam angle on AS_C. It was mostly in YAW but you can also see it in PIT, and the pattern is very repeatable.

Anyway, my objective here is just to place the beam at the center of the Faraday aperture, and I chose this:

New SR2 slider = [2800, 800].

More on the wavy pattern on the plot:

The peak-to-valley in YAW data is as large as 1.5% or so. Does this mean that SR3 scan before/after comparison is useless? No.

During SR3 scan, the beam was shifted by 300 counts in YAW, or about 10mm on SR2. The beam pointing on AS_C was fixed using SR2, so the beam angle on AS_C changed by about 10mm/18m or so, i.e. about 600urad or so.

OTOH, the full scale of the SR2 YAW scan corresponds to the Faraday aperture of 20mm, and that's roughly the beam shift on the pico. The beam position on AS_C was fixed using pico, and pico-AS_C distance is about 14 inches, so the beam angle change over the entire SR2 YAW scan is 20mm/14" = 60mrad or so. This is three orders of magnitude larger than SR3 scan angle change.

If we replotted it as the function of beam angle on AS_C (which I didn't), and put both the SR2 scan and SR3 scan data on the same plot, two data points representing the before/after SR3 scan would be basically on one vertical line in the plot. If this is indeed an etalon type thing on the diode surface, basically SR3 before/after the beam would see the same interference. That's my theory anyway.

another example

Still there, still a problem....

I made a few plots today. The spectrum of the CPS right before and right after the trip, and the zoom-in time series plot around the time of the trip. I notice that the time that the CPS signal goes down does not match the GPS time indicated the trip exactly (off by a few hundred milliseconds).

While making the spectrum I also notice the peak near 4Hz in the "beforetrips" spectrum plot. So I went and look at the LHO summary page and found that there's a small gaussian-looking bump around 4Hz that seems to appear everyday. Probably not very important but just wanted to point that out.

Also, please note that V2, H2, and H1 signals are almost perfectly overlapped (that's why you only see two colors). 

I'll start looking into other related channels that *should* have seen the signals. Although I believe this might be an electronics issue.

Spectra for this quad attached.