Closes WP11693 Dhruva, Julian, Camilla,

After 75894 and HAM8 vent, today we rolled SQZT8 enclosure back to its marked position next to HAM8, replaced the bellows and removed guillotine from the viewport. Fil will recable the enclosure early next week. 

[Sheila, Jennie, Elenna]

Here are some notes about how we by-hand improved the OMC alignment

• Sheila centered the beam on AS_C using SR2 movements by hand
• Sheila ran AS centering loops for WFS A and B until the beam was centered, then turned them off
• we noticed half the range on the OMC suspension is in use on T2 and T3, so Jennie moved OMC sus in pitch to reduce the drive
• Jennie used OM2 for QPD B alignment, use OM3 for QPD A alignment- centered the beams on each QPD by walking the suspensions in pitch and yaw
• Sheila quote to explain the process further: "this is a screenshot I took after I moved OM2 yaw to center OMC QPD B and OM3 yaw for OMC QPD A, with the OMC suspension offsets small. This means that we are off center on the AS WFS DC, but I put offsets into them so that we could close the AS centering loops. Turning on the AS centering loops didn't suppress the 0.5 Hz motion much. Even though the QPDs are fairly close now before turning on the ASC loops, the OMC suspension still saturates in pitch when we turn them on."
• with sensor correction on, things improved because there was less movement overall in the beam
• the results of these movements are shown in the attached screenshot (this is the screenshot referenced in the quote above)
• Sheila successfully ran the OMC ASC and they converged without saturation
• Second screenshot shows the results of running OMC ASC
• I next pico-motored to center the beam on AS A and B in pitch and yaw
• Once I centered the beam, I engaged the DC3 and DC4 loops to check they would run without any issues. They ran just fine so I again turned them off and disabled the picomotor

As a final check I turned on both OMC ASC and AS WFS centering and the loops converged appropriately.

Jeff K, Oli P

In alog 75947 part3, we had modeled the BBSS using what we thought were the correct Final Design parameters and then adjusted the d1 and d4 values* in order to get our model to match how the actual BBSS was responding. However, the parameter set we were using had the boolean variable stage2** set to 0, when the parameter set from the BBSS Final Design document(T2000503) had stage2 = 1. This was a change that I had made due to a misinterpretation.

Because of this mistake, the parameters that we had thought were correct were actually wrong, and so when we adjusted d1 and d4, we were unknowingly fitting to an incorrect model. These results were shared with the SUS group, where it was mentioned that stage2 was supposed to be 1.

We've now rerun the model with the actually correct Final Design(FD) parameters, and have adjusted d1 and d4 to fit our data. This adjustment has d1 = FD - 2.5mm and d4 = FD - 1.0mm, which are smaller changes than when we were using the wrong parameter set (d1 and d4 were increased by 5.0mm and 1.5mm respectively). Attached are our results in pdf form, along with pngs of the transfer functions for Pitch and Longitude, since those are the two most affected by the changes to d1 and d4. This adjusted parameter set can currently be found at $sussvn/Common/MatlabTools/TripleModel_Production/bbssopt_pendstage2on_d1minus2p5mm_d4minus1p0mm.m, but eventually will replace the bbssopt.m that is in that same directory.
Figure legend:
- Black - Model using the wrong Final Design parameters
- Dark blue - Model using the wrong Final Design parameters plus adjustments for d1 & d4 to match data
- Dark green - Model using the correct Final Design parameters
- Light Green - Model using the correct Final Design parameters plus adjustments for d1 & d4 to match data
- Gray - BBSS M1 Transfer Function data

Appendix:
* d{top, 0, 1, 2, 3, 4} is the vertical distance between the break off point of a wire and the CoM for each mass. These values are important for calculating the locations of fundamental modes for each DOF. There are two different types of d's, effective d's and physical d's.
    - The physical d's are the vertical distance between the break-off point of the wire and the CoM of the mass. These values assume an infinitely flexible wire, which isn't the case in real life.
    - The effective d's are the vertical distance between where the wire leaves the clamp and the CoM. Since the wires aren't actually infinitely flexible, they'll start bending before they reach the break off point, meaning we'll have a larger effective d as compared to the physical d.
These two relate to each other as  physical d = effective d - effective flexure point, with the effective flexture point being the extra distance between the clamps and the breakoff point.
In the building of the suspension model, both types are used at different times, so there is a need to be able to swap between them. That's what the stage2** variable is used for.

** stage2 is a boolean variable that determines whether the effective(stage2 = 0) or physical(stage2 = 1) d's are used.
    - If stage2 = 0, the d values are used as effective values, and there are no corrections made to account for the flex of the wires.
    - If stage2 = 1, the d values are taken to be the physical values, and so an effective flexture point is calculated and added to account for the flexing of the wires.
Since we entered in the physical d's, me changing stage2 to 0 meant that the model wasn't adding in the effective flexture point distances, changing our results.

Fri Mar 01 10:08:34 2024 INFO: Fill completed in 8min 30secs

Gerardo confirmed a good fill curbside.

Late entry.

The pressures as of today (March 1st):
HAM7: ~4.7E-7 Torr
HAM8: ~1.3E-6 Torr
Corner: ~1.1E-7 Torr
EX: ~2.2E-8 Torr

Activities on 2-29:
- At the corner, IP1, IP2, IP3, IP4, IP14 ion pumps were valved in
- The controller of IP1 was needed to be replaced, as the current was very unstable. After switching it with the former H2 IP5's controller, it went back to normal
- A safety incident happened with the HAM7 RGA pumpdown: a castor wheel of a Pfeiffer cart fell off, and the cart fell over. HAM7 RGA needs at least a weekend-long pumpdown and bakeout; no further consequences
- Corner (and HAM7) further schedule: Turbo pumps valve-out: 3-4; RGA scan #2: 3-4; GV5 & GV7 open: 3-4; HAM7 and HAM8 valve-in: ~3-6
- EX further schedule: RGA scan #1: 3-1; Ion pump valve-in: 3-1; Turbo pump valve-out: 3-4; RGA scan #2: 3-4; GV20 open: 3-4
- HAM8 was leak tested; all the joints are tight, see in more detail: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=76063

J. Kissel
IIET Ticket 8193

A decade ago, Rana put in the above IIET ticket calling out that we made the QUAD's custom L3 LOCK bank before the RCG was able to ramp the offset, and/or before the ramping of the offset got highlighted yellow during ramping like the gain typically does. I've fixed this issue this morning by grabbing the latest auto-generated versions of these filter banks from

    /opt/rtcds/lho/h1/medm/h1susetmx/
        H1SUSETMX_ETMX_L3_LOCK_BIAS.adl
        H1SUSETMX_ETMX_L3_LOCK_L.adl
        H1SUSETMX_ETMX_L3_LOCK_P.adl
        H1SUSETMX_ETMX_L3_LOCK_Y.adl

and hand copied the filter medm guts over to the

    /opt/rtcds/userapps/release/sus/common/medm/quad/
       SUS_CUST_QUAD_L3_LOCK.adl
then search and replaced "H1:SUS-ETMX" with the macros "$(IFO):SUS-$(OPTIC)" in order to make it sufficiently generic for all QUADs and both sites to use. Also, while there, I took the extra effort to remove all the old "Online Detchar Channels," or ODC channels that were removed and/or deprecated after O2. The updated screen is committed to the userapps svn as of rev 27162.

Attached is the screenshot showing the BIAS offset being ramped as a test (this was the original motivation for the ticket).

This closes the ticket!

TITLE: 03/01 Day Shift: 16:00-00:00 UTC (08:00-16:00 PST), all times posted in UTC
STATE of H1: Planned Engineering
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    SEI_ENV state: MAINTENANCE
    Wind: 29mph Gusts, 19mph 5min avg
    Primary useism: 0.07 μm/s
    Secondary useism: 0.52 μm/s
QUICK SUMMARY:

More PEM work slated today along with more potential OMC and SQZ work for early commissioning

Both access ports on -Y door for HAM8 were leak tested.  The helium background registered at the leak detector was of 4.6x10^-10 Torr-l/s before starting the test.  Both joints were sprayed with helium and no signal above the background was registered by the leak detector.  Final background registered by the leak detector once the leak test was done was of 4.0x10^-10 Torr-l/s.

Jennie W, Sheila, Jenne

Sheila and I moved SR2 yaw to centre the beam on ASC_AS_C QPD.

Then we changed OM1 pitch and yaw to centre on WFS ASC_AS_B.

Then we changed OM2 pitch and yaw to centre on WFS ASC_AS_A.

After this we were able to turn on the DC 3 & 4 centering loops.

The first image shows the alignment at this point.

Then Jenne tagged in.

We aligned OM3 to bring the beam back onto centre on QPD A and B.

At this point we tried to turn on the OMC ASC loops but the OMC suspension saturated.

Accidentally clicked 'Offload OM Alignment' button on centering screen but this did not seem to do anything.

Changed POS X and ANG Y gain signs in servo.

The ASC loops still go running off (ie. do not converge).

We turned back on DC centering 3 loops 3 and 4 to stay centred on the AS_{A,B} but these do not do much to the spots.

Turned on OMC ASC loops and they did not converge and the OMC suspension saturated again.

We think this sign convention is definitely wrong so we flipped POS X and ANG Y signs back.

For reference they now have positive gain in POS X loop and negative gain in ANG Y loop.

Turning on the ASC still saturates the OMC SUS.

We turned on the SR2C P and Y loops to keep the beam centred on AS_C QPD.

The nest thing we tried was aligning SR3 to improve the alignment on A and B QPDs and hopefully stop the OMC suspension saturating (we thought maybe this might improve pointing into HAM6).

I stepped the SR3 pitch up in  steps of 6 microradians and the loops move to correct the alignment with SR2, OM1 and OM2 so this corre4cts the QPD alignment. It was hard to see any change for the better on QPD A and B.

We also tried the same steps for PR2 but down in yaw and this also did not improve the alignment on QPD A and B overall.

I turned off the DC centering and SRC2 loops and we cleared the history for SRC2 which may have changed the alignment somewhat.

Here is the alignment changes we made in the second image.

I also walked back the alignment changes on SR3 and PR2 relative to this image.

Leaving the OMC ASC and OMC length locking off also.

The thirs image shows that Jenne turned the gain of SRC2 up from 10 to 40 so the loop would converge faster.

J. Oberling, F. Clara, T. Shaffer

TJ let me know that the ITMy OpLev signal had gone missing, so I went looking for it.  Checked the laser, found running as normal.  All the electronics looked good, tried power cycling the whitening chassis in the biergarten, signal still lost.  TJ tried moving the ITMy around to see if we were grossly misaligned, but still no signal.  Trending the OpLev SUM, the signal was lost at ~10:34am PST on February 15th.  The only things going on in the biergarten that day were Ryan C. and myself doing water level surveying around BSC2 and Fil pulling cables in the biergarten area.  Fil and I went out to the LVEA and started looking at the cable runs, turns out the original OpLev signal cable was not long enought to get to the whitening chassis in the biergarten, so another cable was used to extend it.  We found the cables disconnected at this point, between BSC8 and BSC1.  Unfortunately, the connection was not secured at all, so our best guess is that while Fil was pulling cables something snagged on the OpLev signal cable and pulled the connection apart.  We have now added some nuts to secure this connection (see attached picture), and the ITMy OpLev signal is now found and happy again.

At LLO, Aidan and Karla found the ISCTEX/Y tables (ALS/HWS) tables were further from the BSC viewport than designed which would change Aidan's T1000717  mode-matching calculations. Ours are also different, EY more than EX. 

TITLE: 02/29 Day Shift: 16:00-00:00 UTC (08:00-16:00 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY:  Lots of work going on around the site - single bounce alignment, RGA heating, lights, and much more.
LOG:                                

WP11736 Power control of end station POE injectors

Dave:

The new end station VEA switches do not have power-over-ethernet (POE) capability and therefore an injector is being used to power the end unit. There are only two POE devices at each of the end stations; the gigabit ethernet camera and the WIFI WAP.

To restore the ability to remotely power cycle the end station cameras, I have installed a pulizzi network controlled power distribution unit in the VEA vacuum racks which controls the power to the POE injector unit. Unfortunately this is an all-or-nothing solution in that the WAP will also be powered down along with the camera.

The pulizzi units are on the 105 slow controls network

Jennie W, Sheila.

I chose a high range time from a lock during O4a, specifically 2024/01/15 21:41:15 UTC, and compared the OPLEV values with todays.

See attached image.

OpLEVs which are the same as in observing: SR3 PITCH/YAW, PR3 YAW, ETMX PITCH/YAW.

OpLEVS which have changed:

ETMY PITCH by +24 cts.

ETMY YAW by -1.8 cts.

ITMY does not count as it is mis-aligned for OMC single bounce measurements.

ITMX YAW by -10 cts.

ITMX PITCH by -5 cts

BS PITCH by +14 cts.

BS YAW by - 10 cts.

PR3 PITCH by 0.2 cts.

Used Sheila's OPLEV template from /ligo/home/sheila.dwyer/ndscope/SUS/sus_op_levs.yml.

(Randy, Mitchell, Betsy)

The West Bay cleanroom work is complete so the large cleanroom has been turned off again.  Room turned off ~9:30am this morning.

(The 4x 3IFO QUAD upper structures have now been moved to their smaller storage containers, relabeled , and ICS records re-organized.  The large ISI storage container that they came out of still houses the 2 Elliptical baffle down tube assemblies and partial TMS telescope subassemblies.  Photo pictures have been also added to the containers for our future selves.)

TJ, Camilla. Aim to check CO2Y laser is at it;s best temperature after recent 76007 power degradation, and we never got the  expected ~50W from this laser after refurb.

I temporarily commented out the temperature checkers in TCS_CO2.py and reloaded for ITMY.

Made a script /tcs/common/scripts/power_adj_scripts/co2_temp_stepper.py to: take the TCS_ITMY_CO2 guardian DOWN, step the chiller setpoint (H1:TCS-ITMY_CO2_CHILLER_SET_POINT_OFFSET), wait 50 minutes, bring the TCS_ITMY_CO2 guardian back up to LASER_UP, wait 10 minutes and then repeat. This is so we can see the laser changing and also a PZT scan (while laser relocking) at each temperature step.

Stepping over chiller setpoints from 19.5 to 23.75 degC in 0.25deg chiller steps. Expect this run 18:00UTC to ~12:00UTC (4am tomorrow) when it will leave the laser in LASER_UP with the setpoint 21.6degC.

J. Oberling, R. Crouch

Update on FARO work during the O4 commissioning break.  Previous updates at the following alogs (with associated comments): 75669, 75771.

Since the last progress update we've been testing our FARO X/Y alignment routines and attempting to re-establish Z=0 based on the door flange scribes on BSC2.  We've been navigating Laser Safe/Hazard transitions, as we can only do optical surveying (like using an autolevel for our BSC2 survey) during Laser Safe; the FARO is usable during Laser Hazard so we've been using these windows for FARO work.

FARO X/Y Alignment Testing

As a means of testing the repeatability of the FARO's X/Y alignments we have been using the brass monuments for mechanical test stand #2 (TS2) in the West Bay of the LVEA.  The FARO gives us a global X/Y coordinate for these monuments based on our alignment (which is also a local X/Y coordinate since X_G=X_L and Y_G=Y_L), which we can use to compare the Measured Local LVEA coordinates to each other and test the repeatability of different FARO alignments.  In addition, each test stand has a monument that represents the [0,0] of the test stand (monument TS2-10 for TS2). We can therefore subtract the local LVEA X/Y coordinate for the [0,0] monument from each measured test stand monument to translate from Local LVEA coordinates to Local Test Stand coordinates.  With this translation we can also compare the monument coordinates measured by the FARO to where we think they are via their as-designed coordinates (designed test stand monument coordinates taken from D1100291).

The results are shown in the attached .pdf file 'FARO_XY_Alignment_Test_TS2_Monuments.pdf'; I have also attached the reports generated from PolyWorks for each of our surveys.  To date we have done this with 3 separate alignments:

• Alignment 1: BTVE-1 as a sphere, PSI-1, PSI-2, and PSI-6 as points
  • Alignment originally created on 2/5/2024 to test differences in using sphere features vs point features; the 3" sphere fit rod was used for BTVE-1 (alog 75771, under Wednesday, 2/7/2024)
• Alignment 2: All alignment monuments as spheres
  • Alignment originally created on 1/22/2024 with a 3" sphere fit rod, to compare to the 5" rod and test the accuracy of moving the FARO (done in alog 75669)
• Alignment 3: All alignment monuments as spheres
  • Alignment originally created on 2/21/2024 as a new alignment for this test; the 3" sphere fit rod was used

Alignments 1 and 2 give us insight into how using different feature types (points vs spheres) for our alignment monuments cause variations in the alignment.  Alignment 3 was used to give some insight into the repeatability when the same alignment feature types are used with 2 different alignments (in this case 'All Spheres' vs 'All Spheres').  The first 3 pages of the results pdf file detail the measurements of the TS2 monuments, the conversion to Local Test Stand coordinates, and a comparison of the measured test stand coordinates to the as-designed ones; 1 page is used for each alignment.  The final page compares the 3 alignments to each other, both in Local LVEA coordinates and in Local Test Stand coordinates.  Some thoughts:

• Designed vs Measured Test Stand coordinates
  • All 3 alignments show significant differences in test stand monument coordinates vs our designed coordinates.  That said, as can be seen from the final page all 3 alignments match each other fairly well, with only a few deviations >0.5 mm.
  • This is somewhat baffling (and a little worrying), as this test stand, with these monuments and as-designed coordinates, were used to align the cartridge assemblies for the ITMx, ITMy, and BS optics during aLIGO install.  I don't recall seeing these large variations in optic position while doing the final alignments once these cartridges had been installed in their respective chambers (need to dig through my old notes from install).
• Alignment 1 vs Alignment 2, comparing Sphere+Points alignment to All Spheres alignment
  • The 2 alignments match pretty well in X, but are off in Y.  Alignment 2 appears to be shifted in Y w.r.t. Alignment 1 by approximately -0.5mm.
• Alignment 2 vs Alignment 3, comparing 2 All Spheres alignments
  • Some variation in X now, with a couple points getting close to 1mm; Y variation looks better, but still several points approaching 0.5mm deviation.
• Alignment 1 vs Alignment 3, comparing Sphere+Points alignment to 2nd All Spheres alignment
  • More variation in both X and Y, which isn't surprising given the variations seen when comparing the 2 All Sphere alignments to each other.  Some variations approaching 1.0mm.

We're still digesting this.  I'm intrigued by the measured test stand coordinates for the monuments in line with each other.  For example, TS2-1 is supposed to be directly in line with TS2-4, only separated along the test stand's Y axis; this is the same for the group TS2-2, TS2-10, and TS2-5, as well as the group TS2-3 and TS2-6.  All 3 alignments show these monuments being at an angle with each other, and a similar angle at that; almost like the line from TS2-2 to TS2-5 (which also intersects TS2-10) was not straight when these monuments were laid out, and that carried over in the setting of the monument groups to the sides of this line (TS2-1/TS2-4 and TS2-3/TS2-6).  I will say that I find the deviations between FARO measured and as-designed test stand monument coordinates particularly worrying; whether that's due to an error in the FARO alignment or an actual error made when these monuments were first laid out I can't yet say, some more investigation is required (could do something like use a 100' survey tape to measure distances between monuments and compare to the FARO measurements).  Also, I would like to to set up a new Sphere+Points alignment to see if using the point alignment feature improves the repeatability; as I've said a few times in the previous alogs, we suspect that the sphere fit routine and the limitations of the sphere fit rods are introducing error into the FARO alignment, and the above alignment comparisons appear to support that at first glance.  I'm interested to see if using points instead of spheres improves this, but we need a new alignment to compare to the old Sphere+Points alignment.

BSC2 Z=0 Water Level Survey

Based on the results of our FARO work detailed in alog 75771, we want attempt to re-establish Z=0.  This was originally done by averaging the 8 door flange scribes of the BSC2 chamber (1 and 3 o'clock and 1 and 9 o'clock on each of the 4 door flanges).  With all of the line of sight blockers (beam tubes, other chambers, electronics racks, cable runs, etc.) we felt the easiest way to repeat this was to use a water tube level.  To do this we used roughly 60' of flexible tubing with an 8mm OD and 6mm ID.  We filled it with water (setting up a siphon works great for keeping air bubbles out of the tube), leaving some air at each end, and set up around BSC2.  One end of the level was fixed to the unused HEPI pier for BSC8, with a scale attached nearby for measurements; the other end was placed along the door flange scribe under measurement.  We used an autolevel to set the water line on the scribe line to be measured, then used a 2nd autolevel to sight the other end of the tube and take a reading on the scale.  We ended up using several rubber bands and some tape to secure the tube to the door flange; the tape was necessary to keep the tube from sagging under the weight of the water (the BSC scribes are over 6' above the ground), while the rubber bands helped to keep it mostly secure while we were setting it on a scribe line.  The first 3 pictures show the setup, with the third one taken through an autolevel to show a close up of the water in the tube (have to sight at the bottom of the meniscus, just like with a graduated cylinder or similar measurement devices (like glass measuring cups in your kitchen)).

We did have a few issues, chief among them being that we could not get the water in the tube to stop moving at first.  We would set the water line on a door flange scribe and watch it settle, and it would keep dropping slowly over several minutes.  We noticed that regardless of where we set the water level, it would always drop to the same point; what finally clued us in to the issue was noticing that the other end of the water level was also dropping.  If the level were rebalancing we would expect one end drop while the other raised, but this was not the case.  At this point we also noticed that, even though we left about 12" of air at each end of the tube when we initially filled it, we now had almost 2' of air at each end.  The solution?  Not enough water in the tube, so add some more.  We did this and all the stability problems vanished.  We could then set the level on a scribe line, and after just a few seconds it would settle out and be very stable.  Best explanation I have is we didn't have enough water to account for the slight compression of the water column at both ends of the level, since our measurement point was over 6' off the ground.  With only a 6mm ID on the tubing, it doesn't take much to cause a big difference in how the level behaves.  By adding ~9mL of water to the tube (using a 2mL transfer pipette) all of our problems were solved.  Second issue, don't step on or touch the water level once set.  This causes the water in the tube to move, a lot.

The other big issue we had is sighting the correct scribe line on the door flanges.  Over the years since site construction several additional scribe lines have been added to many of the door flanges, all within several mm of each other.  Most have no markings on them, a few had arrows, but 1 scribe on each flange was marked with 3 punch marks; this was also true for the 3 flanges with only 1 scribe on them.  So we sighted the scribe line marked by the punches on all door flanges.  The 4th picture shows an example of these punch marks (there are 2 scribe lines in this pictures, one that is straight and one that is not; we used the one that is straight, which can be seen behind the autolevel cross hairs).

With our scribe lines chosen and other issues figured out, we set about measuring all 8 of the BSC2 door flange scribes.  The final picture is a shot of my notes from the survey.  Notice the large separation for the -X door scribes.  Mike Zucker indicated to us that he thinks the scribes were placed to within +/- 1mm of flange center (having a hard time finding documentation of this, he is currently looking for the old "end item data package" for the chambers from their initial construction in the 90s), so this 11.3mm separation in particular is puzzling (we also measured a 4.6mm separation for the +Y door, 1.3mm separation on the -Y door, and 0.5mm separation on the +X door).  One thing he suggested we can do is use a flat survey tape to check that the scribes are on a true diameter of the flange (are they 1/2 circumference apart?), which we will do once we have Laser Safe again.  Once we confirm we've used the correct scribe lines we will continue with using the average of these scribes to check the various height marks around the LVEA.  Should we find that we don't have the correct scribes then we will have to repeat the water level survey.

I. Abouelfettouh, J. Kissel, O. Patane, B. Weaver

Executive Summary: The first article BBSS transfer functions look great. Though there is some confusion about the M1 P 2 P modeled transfer functions drastically disagreeing with the measured TFs, there is a consistent story between 
    - the adjustments to the mechanics that were made during construction and 
    - deviations from the "production" model parameter set that could re-create those construction adjustments. 
Further discussion will be had with the assembly / design team as to the future course of action.
Kissel suggests that -- even as the first article stands now -- the resulting measured transfer functions with the mechanical adjustments would/should happily meet A+ O5 requirements.

%%%%%%%%%%% Begin kLOG (You missed these...) %%%%%%%%%%%%%%

I got a debrief yesterday from Betsy, Oli, and Ibrahim of the comparison between 
    - measured transfer function results from the first article construction and
    - what had been deemed the production model parameter set for the BBSS,
i.e. what's discussed in LHO:75787.

The existing "production" model parameter set starts from Mark's update to the BBSS parameter set post-final-design after adjusting for the production wire thicknesses (see TripleLite2_mark.barton_20211212bbss_production_triplep.m, changed at rev 11625, circa Sep 2023). Oli successfully copied over to the usual matlab formating to create bbssopt.m (created at rev 11734, circa Jan 2024).

At the start of the debrief, there were (only!!) 3 outstanding issues / questions they had:
    (1) The overall magnitude scale for all DOFS for all measured transfer functions was a consistent factor of ~3.15x more than the model estimates,
    (2) After browsing through the EULER-basis drive to OSEM-basis response plots, and some of the off-diagonal EULER-basis showed little-to-no coherence, and
    (3) The measured M1 Pitch to Pitch transfer function's frequency response was significantly different than the model.

For (1), this is typically a sign of a mis-calibration of the data. We reviewed the calibration of the measured data from the processing script, plotBBSS_dtttfs_M1.m, created by Oli and Ibrahim in Nov 2023. The DTT templates that measure the transfer function use the pre-calibrated output of the sensors for response channels i.e. the channels come in units of microns and microradians, so they only need a factor of 1e-6 [meters / micrometers]. The only substantial thing that needs calibrated into physical units during post-processing is the excitation. The review of the calibration of the exciation revealed nothing suspicious in the script based on our current expected knowledge of chain
    - the test stand electronics (an 18-bit DAC = 20 / 2^18 [V/ct]), 
    - BBSS coil driver (a TTOP coil driver, coupled with a BOSEM coil = 11.9 [mA/V]), 
    - 10x10 magnet strength (1.694 [N/A]).
    - (lever arms and numbers of actuators are pre-calibrated out via the EUL2OSEM matrix, generated by make_susbbss_projections..m, and installed in EPICs)
The above factors result in an overall calibration of 1 / 1.5405 [(m/N) / (um/DAC ct) or (rad/N.m) / [urad/DAC ct]] that's displayed in the legend of each of the plots from LHO:75787.

In the end, we were more interested in understanding (2) and (3) rather than getting to the bottom of the calibration. Further, the test stand is some old, pre-aLIGO concoction whose records and modifications are unclear. So we figure we just move on, accepting that we need to fudge the data by the extra factor of 3.15x. We'll get serious about figuring it out if there's still such a discrepancy after moving the BBSS over to the production H1 system.

For (2), all concerns can we waived off with expectations. 
    (a) The first plot of concern was the P to F1F2F3 plot (page 17 of 2024-01-05_1000_X1SUSBS_M1_ALL_TFs.pdf), in that the magnitude of the F2 and F3 TFs were low and/or noisy. This is expected because F2 and F3 OSEMs are along the (center of mass / axis of pitch rotation) of the BBSS's top mass. So they see no pitch by construction (for better or worse).
    (b) The second collection of plots of concern were the off-diagonal DOFs, 
        (i) showing noise and/or 
        (ii) the opposite -- showing well-resolved cross-coupling in DOFs that we *don't* want cross-coupled. 
        We shouldn't be mad about (i) -- e.g. page 7 showing incoherence between L response to V drive and V response to L drive. What power is resolved in those transfer functions -- typically on/around resonances -- is because the TFs were taken undamped an in air. So there's just a ton of movement that an FFT might / cross-correlation might *think* is coherent with the drive, but it's really not.
        We looked closer at any of the off-diagonal TFs that *were* resolved, (ii) -- e.g. page 9 showing well-resolved cross-coupling between R response to V drive and V response to R drive. In each of these TFs, we found that the magnitude of the cross-coupling, off-diagonal TF was less, if-not-MUCH less that the on-diagonal TF, which is good. Where it was close, it sort-of "is what it is." Little attention has been typically paid to mitigating the off-diagonal transfer functions during the design phase of LIGO suspensions to-date. Further, they often are a result of the unique construction of each individual instantiation of the suspension type. There's no much we can do about it post construction, and what we *do* do if it proves problematic to the detector, is dance around the problem with fancy controls techniques if needed.

For (3), we arrive at the meat of this aLOG ::  The *model* of the M1 Pitch to Pitch transfer function looked very weird to me. Betsy mentions the during the construction of the first article they 
    (a) found a discrepancy between the fastener model vs. measured mass budget that resulted in an unclear relationship between the center of mass of each stage and their suspension points (typically called the "d" parameters)
    (b) acknowledged there would be uncertainty in the location of the suspension point for the bottom mass / dummy optic given the wire-loop + optic prism system since the final distances between masses have not been measured.

This, coupled with the fact that no *other* DOFs disagreed with the model besides P to P, led me to suspect the model parameters that only impact the pitch dynamics may be incorrect: 
    (i) each stages' separation between suspension point and center of mass, the "d" parameters, and 
    (ii) the pitch moments of inertia.

For a reminder of the physical meaning of all of the triple suspension parameters, see T040072.

As such, using the bbssopt.m "production" or "Final Design" (FD) parameter set as starting point, we tweaked these parameters by 10%-ish or factors of 2 to gather intuition of of how it would impact the response of the P to P transfer function. As a result, we have come to the conclusion that, in order to explain the data, we need to
    - increase "d1" by + 5 [mm]. This is the separation between the top (M1) mass center of mass and it's M1 to to M2 blade tip heights. In the absolute sense, this is increasing the "physical" d1 from -0.5 [mm] to +4.5 [mm], and
    - increase "d4" by 1.5 [mm]. This is the separation between the bottom (M3) mass / dummy optic center of mass and the wire/prism break-off point. In the absolute sense, this is increasing the "physical" d4 from +2.6 [mm] to +4.1 [mm].

Check out the attached plots which demonstrate this.
Citing discussion of overall scale (1) from above, all *measured* transfer functions have been scaled to the model by a factor of (1 / 3.15). This just makes comparing model to measured frequency response a lot more clear.

First attachment :: comparison between the final design model parameters and a variety of reasonable deviations of d1 between *decreased* by 2.5 [mm] and *increased by 5 [mm]. You'll notice that once d1 surpasses +1.0 [mm], the transfer function starts to look more like a standard triple suspension's transfer funtion. a d1 of FD + 5.0 [mm] lines up well with the upper two resonances of the measured data, but reduces the frequency of the lowest two L and P modes to below the data.

Second attachment :: comparison between the final design model parameters and a variety of reasonable deviations of d4. You'll notice that d4 really only have an impact on the lowest two L and P modes.

Third attachment :: comparison between the final design model parameters and a variety of reasonable deviations of the top (M1) mass' moment of inertia, the I1y parameter. 

Fourth attachment :: comparison between the final design model parameters and a variety of reasonable deviations of the middle (M2) mass' moment of inertia, the I2y parameter. 

Fifth attachment :: comparison between the final design model parameters and a variety of reasonable deviations of the bottom (M3) mass' moment of inertia, the I3y parameter. 

None of the modeled changes to the moment of inertia -- shown in the third, fourth, and fifth attachments -- show promise in reproducing the measured results.

Sixth and Final attachment :: comparison between the final design model parameters and one with only d1 increased by +5 [mm], and d4 increased by +1.5 [mm].

The modified model in this last attachment fits the data the best, so we conclude that the issues with mechanical construction (3a) and (3b) are consistent with the measured data :: the reconfigured mass budget needed from fastener issues resulted in a deviation from design value for d1, and the imprecision of the mass-to-mass distances and wire-loop / prism system resulted in a roughly ~2 [mm] slop for this assembly.

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Big Picture Systems Level Commentary by Jeff :: If these measured transfer functions end up being the reality of the final frequency response of the BBSS -- this will be totally fine. The pitch isolation one gets above the resonances (defined mostly by the moment of inertia) is the same, the lowest L and P modes are sufficiently low, and the details of where the rest of the resonances land are totally inconsequential / amenable to a damping and global control design.