For the careful reader, 
    - the (z:p) = (0.384 : 10.6) Hz comes from the whitening stage. This is what we're changing in ECR E2400330.
    - 5.2e3 Hz pole frequency comes from the transimpedance stage.

As discussed in LHO:83662, the (z:p) = (0.384 : 10.6) Hz is predicted wonderfully by using the component values as drawn in D0901284-v4.

However, if you use the as drawn values for the transimpedance stage, you would expect the high frequency pole to be at
    f_p = 1/(2*pi*R102*C101) 
        = 1/(2*pi*121e3*220e-12)
        = 6.0236 [kHz]

I used 5.2 kHz in the model above to force the (model/meas) ratio for channel 1 to (unity magnitude) & (zero phase), and it worked well enough for the other channels that I didn't bother changing it.
If we take that "measured pole frequency" along with the measured R102 values, that instead suggests that
    C = 1/(2*pi*R102*f_p) 
      = 1/(2*pi*120.1e3*5.2e3)
      = 254.8 [pF]

If we're talking component value discrepancies on the order of 1 kOhm out of 120 kOhm and 30 [pF] out of 220 [pF], that result in a lower pole frequency to the tune of 800 Hz out of 6 kHz and that pole frequency doesn't matter for the control system that these OSEMs -- then I don't care, and you shouldn't either.

Thank you for reading my deep cuts, careful reader. 
See you, Space Cowboy...

Today, Sheila and I followed up on this, and the results are a bit confusing, but somewhat promising.

To start, Sheila reran the "brontosaurus plot" measurement, where FIS is injected to help determine the SRCL offset. She reports this work here.

While she changed the SRCL offset, I once again monitored the AS RF72 and POP X signals. As Sheila changed the SRCL offset, the offset in POPX did change the same way as I saw yesterday, which is not that surprising.

Then, when Sheila set the SRCL offset to zero, I tried opening the SRC1 loop and moving SRM around. The first thing I noticed is that the calibration I calculated yesterday seems bad, since I was adjusting the SRM yaw by 11 urad (according to the slider calibration), but the change in the POP X yaw offset corresponded to less than 1 urad (according to my measured calibration from yesterday).

I moved yaw in only one direction, with the goal of seeing if I could reduce the POP X yaw offset. However, I gave up after 11 urad because it didn't seem to be doing much at all except to small effect on POP X yaw.

Next, I tried moving SRM in pitch. I went the positive direction, and Sheila and I immediately saw the buildups get worse, so then I went the other way and the buildups got better! This corresponded to a 20 urad change in SRM pitch, according to the alignment slider. The change in the POP X pitch offset was minimal.

We also saw kappa C increase quite a bit, almost too good to be true, so we didn't trust the value since we had a large SRCL detuning at the time. Sheila did see that the change in the SRM pitch had an effect on the squeezing as well.

However, Sheila then determined a better SRCL offset of -382, so we went there, and the kappa C leveled off to 1.02, which was better than our current nominal value of 1. This seemed to hold. Then, I stepped the SRM pitch offset back to the starting alignment and the buildups decreased and kappa C went back to 1.

Following the buildups, there seems to be a better alignment of the SRM in pitch. At this time it seems like yaw has no effect, but I only moved in one direction. I think that, whatever the SRCL offset is, we should move the SRM around in pitch and yaw and see if there is an improvement to be found in the buildups. My current hypothesis is that the RF72 dark offsets are creating some alignment offset in the SRC. After we find a good SRM alignment position, we can recheck the SRCL offset, hopefully with both a squeezing measurement and a sensing function.

We should also probably check the whitening on RF72, maybe next Tuesday.

These results are making me think that probably POP X Q would not make a good signal for SRC alignment, since it is dominated by the SRCL offset.

The first ndscope attached are showing the behavior of the POP X and RF72 signals while changing SRM alignment. The second shows the buildups and kappa C when changing SRM pitch and SRCL offset from 0 to -382.

Plot attached, we think that the SQZ is worse at NLG 10 that the other NLGs and we are considering running with NLG = 14.

Here's a fit of Camilla's data, it shows that our OPO threshold has increased compared to 83070, and we still have the same efficiency for squeezing, which implies 6% unexplained loss, which hasn't been fixed by moving the crystal. 

This plot was made using this script

We decided that an OPO TRANS setpoint of 105uW for an NLG of 14 gave us slightly better squeezing, see attached BLRMS. Leaving this in.

If the Operators have any issues keeping the OPO locked at this higher output power, they could lower it slightly following the instructions in 70050 to drop it down to 100uW or 95uW.

18:48 Back to NOMINAL_LOW_NOISE

Within the same ~15 seconds of the lockloss, we turned the CO2 powers down form 1.7W each to 0.9W each. In the hope of doing the thermalization tests we tried last week 85238.

We checked the lockloss today and LSC channels at the time last week we turned the CO2s down and see no glitches corresponding with the CO2 waveplate (out of vac) change, we think the lockloss was unrelated.

With regards to ENGAGE_ASC_FOR_FULL_IFO, the three locks that we've had after the adjustment made yesterday have made the state take an average of 4.5 minutes to get through. Before making this change, it was taking us an average of 8.5 minutes (looking at the four locks before this change), so this has made a big improvement for this state!

However, it looks like the main reason why this state still takes a pretty long time compared to most other states is because it's still needing to wait a long time for the PIT3 and YAW3 ADS to converge (ndscope). Here's the log from this last time that we went through ENGAGE_ASC and you can see that most of the time is waiting for ADS. The actual wait timers in there are only 50 seconds of waiting, so the rest of the wait timers (the one second timers) are just from the convergence checker.

I updated the POP A yaw offset so that PRC1 in DRMI will bring the PRM closer to the full lock point and hopefully make convergence in this state faster.

It may be difficult to see in a standard spectrum, but can be clearly seen in Fscan plots linked off of the summary pages. For the "observing" Fscan, the interactive spectrum plot shows the 2 Hz comb marked automatically. See the attached image of H1:GDS-CALIB_STRAIN_CLEAN

Verifed that the cabling has not changed since 75876.

Next steps we should follow, as listed in 75876 would be to try using a different power supply or lowering the voltage to +12V. Or, there is a note suggesting Fil could make a new cable to power both the camera and CLink's via the external supply (14V is fine for both). 

Thanks Camilla. If anything can be done more rapidly than waiting another week, it would be very much appreciated. Continuing to collect contaminated data is bad for CW searches.

Matt and I turned down the Voltage supplied from 14V to 12V for each camera at ~22:00UTC when the IFO was relocking. Verified HWS cameras and code still running.

We also will plan to have Dave reimpliemnt the hws_camera_control.py script he wrote in 74951 to turn the HWS's off in Observing until we fix this issue.

The 2 Hz comb is still present in H1:GDS-CALIB_STRAIN_CLEAN after the voltage change (before the software update)

I ran SRCL and MICH injections today as a part of determining if the feedforward is performing well, but I repurposed those injection times in the noise budget templates so now SRCL and MICH are complete as well.

After running some PRCL injections to test the feedforward I was also able to update the PRCL noise budget template.

I also reran the jitter noise coupling measurement, since it seemed like the coupling was overestimated at low frequency. The jitter noise had been run very early on in vent recovery, so I am not sure what changed to affect the low frequency coupling (could be the pumps, LSC feedforward, ASC, etc) but now the low frequency coupling is very reduced.

These large BS PIT changes began 5th to 6th July 2024 (plot). This is the day shift from the time that the first lock like this happened 5th July 2024 19:26UTC (12:26PT): 78877 at the time we were doing PR2 spot moves. There also was a SUS computer restart 78892 but that appeared to be a day after this started happening.

Sheila, Camilla

This reminded Sheila of when we were heating a SUS in the past and causing the bottom mass to pitch and the ASC to move the top mass to counteract this. Then after lockloss, the bottom mass would slowly go back to it's nominal position.

We do see this on the BS since the PR2 move, see attached (top 2 left plots). See in the green bottom mass oplev trace, when the ASC is turned off on lockloss, the BS moves quickly and then slowly moves again over the next ~30 minutes, do not see simular things on PR3. Attached is the same plot before the PR2 move. And below is a list of other PR2 positions we tried, all the other positions have also made this BS drift. The total PR2 move since the good place is ~3500urad in Yaw.

• Different time May 21st to 24th 2024:
  • BS Oplev Drift
  • Plot shows 30urad M1 drift
  • PR2 Alignment Sliders P: 1435, Y: 1130
• Pre July 5th 2024:
  • No BS Oplev Drift
  • Plot shows 5urad M1 drift
  • PR2 Alignment Sliders P: 1565, Y: 3210
• July 5th 2024 to 6th Feb 2025:
  • BS Oplev Drift
  • Plot shows 50urad M1 drift
  • PR2 Alignment Sliders P: 1535, Y: 2785
• 6th Feb 2025 to 10th Feb 2025:
  • BS Oplev Drift
  • Plot shows 30urad M1 drift
  • PR2 Alignment Sliders P: 1480, Y: 1195
• 10th Feb 2025 to now:
  • BS Oplev Drift
  • Plot shows 30-40urad M1 drift
  • PR2 Alignment Sliders P: 1430, Y: -245

To avoid this heating and BS drift, we should move back towards a PR2 YAW of closer to 3200. But, we moved PR2 to avoid the spot clipping on the scrapper baffle, e.g.  77631, 80319, 82722, 82641.

I did a bit of alog archaeology to re-remember what we'd done in the past.

• In August of 2015, we found that we were struggling with PR3 pitch alignment jumping, then cooling down upon lockloss.  Alog 20268 talks about the implementation of the lock loss compensation, which first appeared in ISC_DRMI guardian in rev 11228.
• At some point (I didn't dig to find out when precisely), we also implemented the same filters for BS pitch.
• By Jan 2020, both BS and PRM had the soft ASC turn-off.
• In Jan 2020, ISC_DRMI rev 20905 we removed this soft ASC turn-off for both PR3 and BS.  The referenced alog 54709 notes that we shouldn't need those anymore, since we had installed wire heating baffles, to prevent the wires from being illuminated and heating up.
• We haven't had the soft turn-off filters in use since 2020, about 3 months before the end of O3b.  This may be why Camilla saw that we were seeing BS drift at the end of O3b.
• Perhaps our alignment during O4, until we moved the PR spots in May 2024, was such that we weren't susceptible to this wire heating.
• I don't think PR3 is seeing the same kind of trouble that it did back in 2015 upon lockloss, so I think its wire heating baffles are working as designed, so no need to make any changes to the PR3 controls.
• Sheila made the point that because we unclipped some of the +Y side of the beam (without moving the spot on the BS), maybe there is a bit more light that is illuminating the barrel of the BS or getting to the wires.  Or, something?  Without having looked at the actual drawings, I could imagine that the wire heating baffles are working better on PR3 than they are on the BS, because we hit PR3 much closer to normal incidence, whereas with the BS the light could be sneaking around the baffles.  Robert thinks that light could get inside the cage baffle and reflect around and be hitting and heating the wires.
• All of this seems to say that we should re-implement the soft ASC turn-off for the BS. I had a quick look at the 1/e time for the BS to move after lockloss (it's about 241 seconds), and the 1/e time for the filters (about 240 seconds, despite my quoting in alog 54706 that they were 25 min filters (2*pis are hard!)

To put back the soft turn-off of the BS ASC, I think we need to:

• Disable the BS M1 ASC lockloss trigger.  Jeff reminded me that this would foil my plans, since it turns off the ASC signals to the EUL2OSEM matrix.  This will mean that neither the Pit nor the Yaw BS M1 signals will be shut off by the lockloss trigger.  To disable, we'll need to set H1:SUS-BS_M1_TRIG_ASC_ENABLE to zero (which means that the ASC signals will always be passed to the EUL2OSEM matrix).  I don't think this is in guardian anywhere, so we should only need to change it and then accept in safe and observe snap files.
• Change ISC_DRMI around line 66 such that BS pit gain is not set to zero.  Also, have it turn off FM1 in addition to turning off the input.
• Change ISC_DRMI around line 141 to not hit the BS pit RSET button.

Camilla made the good point that we probably don't want to implement this and then have the first trial of it be overnight.  Maybe I'll put it in sometime Monday (when we again have commissioning time), and if we lose lock we can check that it did all the right things.

I've now implemented this soft let-go of BS pit in the ISC_DRMI guardian, and loaded.  We'll be able to watch it throughout the day today, including while we're commissioning, so hopefully we'll be able to see it work properly at least once (eg, from a DRMI lockloss).

This 'slow let-go' mode for BS pitch certainly makes the behavior of the BS pit oplev qualitatively different. 

In the attached plots, the sharp spike up and decay down behavior around -8 hours is how it had been looking for a long time (as Camilla notes in previous logs in this thread).  Around -2 hours we lost lock from NomLowNoise, and while we do get a glitch upon lockloss, the BS doesn't seem to move quite as much, and is mostly flattened out after a shorter amount of time.  I also note that this time (-2 hours ago) we didn't need to do an initial alignment (which was done at the -8 hours ago time).  However, as Jeff pointed out, we held at DOWN for a while to reconcile SDFs, it's not quite a fair comparison. 

We'll see how things go, but there's at least a chance that this will help reduce the need for initial alignments.  If needed, we can try to tweak the time constant of the 'soft let-go' to further make the optical lever signal stay more overall flat.

The SUSBS SDF safe.snap file is saved with FM1 off, so that it won't get turned back on in SDF revert.  The PREP_PRMI_ASC and PREP_DRMI_ASC states both re-enable FM1 - I may need to go through and ensure it's on for MICH initial alignment.

RyanS, Jenne

We've looked at a couple of times that the BS has been let go of slowly, and it seems like the cooldown time is usually about 17 minutes until it's basically done and at where it wants to be for the next acquisition of DRMI.  Attached is one such example.

Alternatively, a day or so ago Tony had to do an initial alignment.  On that day, it seemed like the BS took much longer to get to its quiescent spot.  I'm not yet sure why the behavior is different sometimes.

Tony is working on taking a look at our average reacquisition time, which will help tell us whether we should make another change to further improve the time it takes to get the BS to where it wants to be for acquisition.