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

Executive Summary: For now, we can damp the BBSS Glass BS with BOSEMs and old Level 2 BSFM Glass BS damping loops as long as the L and P EPICs gains are -0.5, all other DOFs are -1.0, and we turn OFF all DOFs of the BSFM bounce/roll mode notches.

Debugging damping loops for BBSS with BOSEMs mounted to the table cloth, we found that with direct copy of "old" level 2 damping loops for BS (a BSFM) was unstable, ringing up in L and P at 2.668 Hz (measured with t-cursors on an ndscope session). 

This is not a huge surprise; we'd already modeled the phase margin with this direct copy SWG:12301 has very low phase margin (modeled to be 23.8 [deg], with the highest upper unity gain frequency crossing at ~2.5 Hz; see dampingfilters_BBSS_2025-07-09.pdf page 33). Plus, experience has taught us that measured TFs often have more phase loss than models, so the phase margin of the loops is likely even less -- hence instability from 1/(1+G) gain peaking.

Ibrahim took some preliminary undamped TFs to confirm the (undamped) dynamical TFs of the BBSS with a glass optic. With what poor coherence we have in air, we can at least eye-ball confirm that they're not substantially different from the metal build on the test stand. Good! Great! We'll try to get these TFs better and Ibrahim will post for reference.

OK, with the dynamics checked out, on to the damping loops. Thus far the team had just rammed all the Level 2 BSFM loops on with a gain of -1.0, as we'd run them for years with the BSFM BS.

So, we did the dumb things first: 
    - We turned OFF the BSFM's BS highest bounce ("SB17.79" FM8) and roll ("SB26.06" FM9) mode frequency notch filters. We know these are the wrong frequency, and they're just eating up phase. (We plotted them, and it's not much at ~2 Hz, but they're the wrong frequency for a BBSS, so we just turned them OFF.) 
    - Turned on DOFs one or two at a time to narrow down which DOF(s) are problematic. T, V, R, and Y close fine and are stable with the old BSFM filters with a gain of -1.0. L and P are the loops that buzz at the 2.625 Hz (0.005 Hz resolution ASD with DTT).
    - Just reduce the overall gain of the loop(s) -- tried P at -0.5 and -0.25 with L still at -1.0. That was still unstable. But, L, P = -0.5, -0.5, is nicely stable, and damps stuff.

Getting slightly smarter, we checked in with the hard work of Vlad from LHO:81178 and found that the L and P filters have an EPICs gain of -1.0, and are identical in frequency response -- but the *filter* overall gain is a factor of 1.88x lower (i.e. essentially a factor of 2.0x). So -- he had to do essentially the same thing we did (though if I know Vlad, he actually measured this factor of 1.88x rather than blind guess like we did). Note that LLO's already using QOSEMs.

So, for now, we have something stable. Over time, we'll work on improving it, but this'll do. Once we have time, we'll take open loop gains, see exactly where we need phase, and adjust. Smart: Shouldn't need that much, change honestly. 
Just as I said in the acceptance review; Slides 33 and 34 of E2500057, we can easily relax the P low-pass filter and then regain the on-resonance pitch damping that we lost from dropping the overall gain by 2.0x.

Rebooting as part of regular maintenance.  Should be quick.

WP 13259
ECR E2200043

The CS HEPI system is planned to be upgraded to a Beckhoff PLC system. Modifications to the motor control panels to readout the VRD readback signal completed. Cabling and panel connections cleaned up. Part of ECR E2200043.

Prior to starting work:

1. All pump stations were locally powered off via the front panel OFF button
2. Breakers to pump stations powered off
3. An anti-static floor mat and a grounding wrist strap used when working on the control panels

Mitchell and I placed the new central beard baffle with a cutout for SPI on HAM2. It went on without issue after Mitch reminded me how to adjust the panels.

I then attached the accelerometer to the L bracket and tried hammering in various places. There wasn't much real estate, so I'm not sure how this will turn out. Data still needs to be analyzed, and I'll post pictures of hit locations then as well.

TITLE: 05/26 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    SEI_ENV state: MAINTENANCE
    Wind: 3mph Gusts, 1mph 3min avg
    Primary useism: 0.03 μm/s
    Secondary useism: 0.57 μm/s 
QUICK SUMMARY:

Tuesday Maintenance day today!

Work stations updated and rebooted.  This was an OS packages update. Conda packages were not updated.

J. Kissel, [S. Koehlenbeck remotely supporting]
(Belated aLOG)

Working with Sina over zoom, we tackled several of the issues reported in the last update (LHO:90313). In the discussion below, I use the same numbers as the issue list from the last update; they were prioritized, so I tackled things and had successes (and one failure) in that order.

The good news first:
    (1) FORWARD The issues with the low (then 35%) efficiency on the REF IFO were merely that I hadn't spent enough time walking the beam around. In the end, without adjusting the REF beam's input alignment at all, I was able to lock down the alignment set screws M_B2 and M_M3 which steer the MEAS beam into the IFO, while having IFO REF A reporting 99.0% efficiency, and IFO REF B reporting 97.2% efficiency. Very very excellent. 
        Final answer 
             (both traces at 1.0 [V/DIV])
             (only measurement of positive leg, not fully differential)
             (room lights and clean room fan off)
	     o-scope measured PEAK to PEAK (i.e. amplitude AMP) REF A and B = 4.04 and 4.12 V
	     o-scope measured MEAN: REF A/B = 2.04 and 2.12 V
	     Efficiency AMP / (2*MEAN): 
                 REF A = (4.04 / 4.08) = 0.99
                 REF B = (4.12 / 4.24) = 0.972
    Attachment 1 shows a picture of the o-scope with evidence of these numbers.
    Let's hope this sticks -- it gives us a LOT of confidence about what these IFOs (and laser delivery system) are capable of once alignment has been optimized and and other issues have been mitigated. I also still see no evidence that the REF IFO efficiency "breaths" on the ~minutes time scale like I've seen with the MEAS IFO.

    (2) FORWARD Speaking of the MEAS IFO, along its MEAS beam path I addressed the issue with QPD B's reflection being wildly off in yaw. I was able to adjust the physical yaw position of OL_QPD_B with the slop in the enclosure's bolt holes such that the QPD reflection landed comfortably on the D_OL_QPD_B dump as it was originally; QTY 2x of the 1.0 x 0.75 [inch] plates (D1800140 Type 07). Said differently for clarity: I swapped out the QTY 2x of the 1.68 x 1.68 [inch] plates I cobbled together that was causing potential clipping issues (LHO:90315. I then centered the beam on the QPD using M_M1 as the steering mirror and and the QPD readout voltages as the metric for "centered." 
        Final answer
            (all traces at 2.0 [V/DIV])
            (only measurement of positive leg)
            (room lights and clean room fan off)
                                                         -X
            CH1  |  CH2          6.13 V  | 6.11 V         ^
            -----------  =       ----------------         |
            CH4  |  CH3          6.18 V  | 6.62 V         .---> +Z

     Attachment 2 shows a picture of the o-scope with evidence of these numbers.
        I was not able to find a position on the QPD where every quadrant was balanced (and thus presumably the beam was truly centered) with my hand-adjustments of the picomotor knobs. But -- I was able to consistently get positions where 3 quadrants that were equal to within 50 [mV]. This is not worth fighting in the lab, since then return beam will be entirely different, and we can and will need to use picomotors with digital actuation.

Now the bad news:
    (3) BACK While then "finishing up" the on-board alignment, I found I was unable to find *any* beam steering with M_B4 and M_M2 that could achieve any higher efficiency than 50%. And this is the IFO that had 72% efficiency "easily" on 2026-05-19 (LHO:90289).

    Because I spent the rest of the day in the lab focused on finding an alignment that worked, I didn't get the chance to investigate any of the breathing. So we stopped for the day, worried that I was optimizing the alignment during on of the "breathing" episodes. So -- no progress on the problem what we really wanted root out AND we made things worse. Remember, we need >75% efficiency -- especially on this IFO, our primary measurement. So, it's not like we're hand-trimming the tips of the grass we've already mowed.

    ACTIONS/IDEAS:
        - The REF IFO beam is clearly great, given the awesome efficiency of the REF IFO. So it's gotta be something going on with the MEAS path to the MEAS IFO. 
            . Check the MEAS path beam positions on M_M1, M_B4, M_M2, and M_B3, and make sure we're not close to the edge of one or more optic.
            . Check -- quantitatively with a power meter, not just via card -- that we're not clipping thru the periscope 45 deg adapter mounts.
            . Inspect the optical surfaces of the mirrors, make sure we haven't incurred any damage or schmutz.
        - We found that the picomotor adjustment screw's SS ball bearing tip for the pitch / vertical actuator of M_B4 looks suspiciously smaller than other actuators on M_M1 and M_M2. The suspicion being that the too-small ball is inhibiting the kinematic adjustment of pitch, making reproducability in alignment a challenge. Maybe when I was assembling them (LHO:87497), a too-small SS ball got in the mix. The drawing for the 830X-UHV Picomotor (E1000197) says this should be a 4.8 [mm] = 0.188976 [inch] diameter ball bearing (rounded up to 0.19 [inch] in the drawing; or vice versa, 0.19 [in] was rounded down from 4.826 [mm]). Could very well be that I somehow found a 0.1875 = 3/16 [inch] SS ball bearing. So, I'll do some spares-kit diving to see if I can swap out this ball bearing.
        - If worse gets worse, we're also going to pull the IFO MEAS PD, and set up a beam profiler. If one can't find good efficiency with alignment alone, then the suspicion becomes beam quality. If we find the MEAS beam into the MEAS IFO is of poor quality, I'm hoping that some of the "would definitely distort the beam quality" ideas from above will solve the issue. But if we don't see anything, we'll at least have another metric as to why.

In other, neutral news:
    (1) While trying to rule out other issues with the REF IFO, before I found success in alignment, I checked every single mirror / beam splitter on the board and confirmed that it had its reflective surface facing the right direction. I also confirmed that the alignment of the M_F1 beam, transmitted thru M_B1 and M_B2 landed well-aligned on to the FBT_PWRIN_MEAS PD, with an iris in hole 88.

    (4) I checked how secure the fiber collimators' tiny-tiny set screws were on the ferrule of their incoming optical fiber. This was in hope of finding something obvious regarding p-pol transmission dependence on physical position of optical fiber. It's a completely indescribably feeling of how tight they need to be, but "you can tell when its too tight," and too tight *sometimes* results in the symptoms I was seeing regarding changes of physical positioning of the fiber impacting the output polarization (due to the set screw spoiling the polarization maintaining properties of the fiber, causing some yucky birefringence). It can also be too loose, too, and that just results in the optical fiber ferrule being able to move within the collimator, changing beam alignment out of the collimator.
    
    The M_F1 collimator's ferrule set screw felt "just right." It was secure, and it didn't take any finger strength with the tiny 1.2 [mm] flat-head driver to loosen or re-secure a few times with "just barely tool tight, using no actual pressure."
  
    The R_F1 collimator's ferrule set screw did feel "too tight." And it this REF fiber's position that I noticed had the most affect on the p-pol power transmitted when I re-noticed the issue. After re-securing the fiber "just right," I no longer saw obvious fiber position dependence of p-pol transmitted power.

    I call this "neutral" news because we're going to have to disconnect and reconnect the optical fibers again to install these feedthrus in the HAM3 chamber. So, "lesson learned" but we're gunna need to check for such dependence again once the transceiver is in the chamber.

    (5) Have not yet cracked open the FBR_PWRIN_REF PD to find the source of the (we suspect) alignment issue.

    (6) Phase drift of MEAS IFO w.r.t. REF IFO. Remember -- suspected non-issue, suspect its a feature of air-currents. So I didn't follow this at all. But will do the "wave your hand above the breadboard" check again once I get the efficiency of the MEAS IFO back up.

    (7) Sensitivity of the IFOs to flicking of either MEAS or REF fiber. Remember -- non-issue -- this is why we have the REF IFO. Anything that distorts the phase in both the REF and MEAS IFO simultaneously is a non-issue, since we're taking the difference.

(Betsy, RyanC, Jason)

Friday we spent more time understanding why the Yaw mechanics weren't effective on the BBSS. We found that a lot of the top mass OSEMs interfere a lot when adjustments are made so they were constantly hanging up and giving us false reading of our adjustments. So we ended up disassembling half the suspension, stripping all top BOSEMs and the middle stage 4-BOSEMs via the entire plate. Then we started to see actual Yawing with the adjustments. In the process however, we stripped one of the 10 blade locking screws. So more disassembly to remove the sheet plate and eventually the bolt.  We now have yaw in the ballpark, but need damping. Facepalm. So will resume reassembling the whole suspension and get damping going asap next week.  Will need to revisit the L measurement after we finish Y and P.

Gerardo, Travis, Jordan, Sean (GNB tech)

Today a tech from GNB came to the site to perform maintenance on the air cylinder for GV7 after we were unable to hard close the valve, see alog 89625

We first soft closed GV8 (and replaced the faulty air regulator) as a safety during the GV7 work. We then marked and measured the positions of the reed switches on the cylinder threaded rod, then disconnected the top air line. Sean then disassembled, cleaned and replaced all of the seals in the cylinder head, and the top and bottom flanges. We did have to modify the wear band since the one in the repair kit was too long and the ends overlapped. We also installed the new cylinder, but the used one looked to be in good condition. We will keep that one as an emergency spare.

New grease was applied to all seals and the inside of the cylinder. In order to keep the seals and wear band contained while installing the cylinder, Sean used a plastic band around the cylinder which kept the seals in place as the cylinder passed over them, which was then removed once the cylinder made it past the top piston seal. The top flange was then installed, along with the reed switches and air line.

The valve was already soft closed during the repair, so to test we wanted to see if we could hard close. We noticed there was no longer any air leaking from the solenoid manifold, and we heard the audible "thunk" of the valve camming over (hard closed) at 40 psi, we confirmed the cds screen showed red for the valve status indicating the valve was hard closed. We then re-opened GV8.

No significant issues encountered, just a lot of cleaning of the old grease and seal grooves.

Full set of pictures/videos will be posted to the DCC and linked to this alog.

Closing WP 13256

(Jordan V., Travis S., Richard M., Filiberto C., Dave B., Patrick T., Jonathan H., Brandon P.(RMC), Gerardo M.)

(Work done on 5/21/2026)
The new purge air compressor, Kobelco KN-0, developed a very small oil leak (again).  A few weeks ago oil started oozing out of some of the oil line connections, about 3 different spots.  See photos.  Technician Brandon Pimentel showed up Thursday morning, and not only did he found the above mentioned slow leaks, but he discovered that the oil pump was also leaking (again), the seal at the drive shaft is not sealing.  That was the diagnosis, see report below.
Brandon turned the compressor off, then proceeded to fix leaks.  The oil pump will get replace later, he has order a new pump and should be here in the next couple of weeks.  The compressor was turned back on, it started working without a problem, "BUT" the HMI (control panel) did not returned!  After several tries at restarting the unit, Brandon and Field Engineering called HMI dead, and it needs to be replaced.  The HMI unit should be here within a week.

Meanwhile we were flying blind, the compressor is doing its job and compressing air and working with its regular schedule, but due to the oil leak on the oil pump, we've decided to attach a thermocouple to the compressor to keep an eye on the oil temperature, same location as the oil temperature sensor the HMI unit uses, then thanks to many people we now have a CDS signal for the oil temperature, see Dave's entry.
We let the unit run until the dew point at the drying towers was acceptable, then we released the purge air into the LVEA, we let the purge air run on the lines inside the LVEA for another hour, then we took a dew point measurement at the point of use, we read -43.7 ^oC.  Then we allowed the air into chamber and purged the chambers for 1 hour before allowing in-chamber work to resume.

Below is Brandon's report:                                

1/4IN OF OIL IN CABINET CUBICLE BELOW OIL PUMP. CLEANED UP OIL RESIDUE FROM ALL COMPONENTS.
REPLACED ORING ON OIL PUMP INLET LENS FITTING. TIGHTENED LENS FITTING BUSHINGS.
TEST RAN UNIT LOADED FOR 1 HOUR INSPECTED OIL PUMP HOUSING FOR EVIDENCE OF SHAFT LEAK AND COUPLING WEAR. FOUND 1/4 OF OIL INSIDE HOUSING AND RESIDUE ON SHAFT. NEED TO REPLACE OIL PUMP.
HMI IS BLACK-SCREENED AND UNRESPONSIVE. PER FIELD ENGINEERING, NEED TO REPLACE. UNIT IS OPERATIONAL.

TITLE: 05/22 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY:
Major work that was completed today: 
Gate Valve 7 is now repaired. 
L4Cs went insideHAM2 . 
Faroing yaw in the new beam splitter.
And Optics cleaning of CRS optics.
 

LOG:

Mitch, Jim

We got a window this afternoon to try installing L4Cs in HAM2. We just did the horizontal L4Cs and cables, because those were the most difficult, but least in the way parts. The H3 L4C in particular was very difficult, I had to go in and work under the SPI ISIJ telescope, laying on my stomach in the beam tube, while trying not to kick the modecleaner baffle out of place. Also, the gap between bottom edge of St1 and the bottom of the nozzle to the modecleaner tube is just slightly narrower than my elbow, so I could fit my arm in there, but was never sure it would come back out easily. Anyway, the hard part is done, we will finish the verticals next week sometime. I also need to get back with Fil about running the in air cables to the feed thrus. We should have the in rack electronics next week some time as well, so I will try to get the adc wiring in the model set up before interface chassis arrives.

[Shoshana, Ryan S]

Yesterday we began building the second set of CRSs sent over from LLO (mostly just putting in heli-coils). I (Shohana) will probably continue working on them today

For some of the parts sent over from LLO (where they had already gone through clean and bake) we found some black residue in some of the aluminum foil wrappings and on the parts (specifically the cross beams [D2300102] and the solid supports [D2300144]) some of which would come off when wiped, but some of the residue would not. Pictures below

(I learned from T0900486 "IO Stray Light Analysis and Baffle Design" that the IFI input baffle is called HA3, IFI output baffle is HA6, the baffle right in front of IM4 is actually supposed to be a pair of HA12-a and HA12-b but there's only one baffle which I suppose is HA12-a, two-hole baffle for ISS array is HA11, and the last IFO REFL before the beam leaves HAM2 is HA13.)

Clipping on the IFI input baffle (HA3) might not be real

The beam spot on this baffle was OK before we did anything to IM1 on Tuesday (IFIinput_before.jpg). It's low and toward +X, but nowhere near clipping.

This baffle is right in front of the calcite wedge that deflects the IFO REFL beam away from the incoming beam path from IM2 (HA3_calcite_wedge.png). The lever arm from the wedge to the baffle looks to be an inch or so at most. Hard to imagine that the REFL is clipped while forward going beam is not, but the scattering goes away when I block the beam between PRM and IM4.

The reported "IFO REFL beam clipping" on this baffle is either because the PRM is not retroreflecting, or maybe it's some kind of ghost beam produced from the PRM reflection somewhere.

If we establish that the main IFO refl is NOT clipped when PRM retroreflects, we don't have to worry about this baffle too much (though ghost beam is still a problem).

We will have to bring a card with a hole to make sure that the beam is retroreflected as good as we can.

FYI, IFIinput_aftercentering.jpg shows the same baffle after we made a huge change in IM1.

We THINK that the beam on the IFI output baffle (HA6) is OK too but we need to check

We don't have any good view of that baffle so it's hard to assess, and we forgot to check it before making changes to IM123.

However, given how small the change was on IFI input baffle, we don't expect that it was very bad before. We'll have to revisit and confirm.

IMC beam spots

As of now, the measured beam position in front of MC mirrors are as follows this. For measurement points, see mc_beampos_measurement_cartoon.jpg. The height is pretty good for all. MC3 is great horizontally too. Beam spot on MC2 and MC1 are both shifted in -Y direction.  MC2 by 3.6+-1mm, MC1 by a couple +-1mm.

Horizontal positions were determined by covering half of the beam with a vertical hard edge (ruler etc.) and then measuring the position of the edge relative to the neighborhood screw holes using a small ruler, and then using the drawings (D0901088, D901089, D0901099) as well as other IO documents (e.g. T0900486) to figure out the nominal beam location. As an example of tedious work done, see ham2mc1.png. Due to the way it was done, we cannot determine the horizontal position of the beam much better than maybe 1/2 of the beam radius. I just put +-1mm error for all measurements. Height numbers were measured off of a ruler, the error bar (if any) is the difference between Rahul's reading and mine divided by two.

What if we move MC2 or MC3 beam spots (or both) to unclip IM4 baffle (HA12)

To get more sense of magnitude of IMC motion relative to the beam motion on IM4, I calculated how much the IMC alignment should be changed to move the beam on IM4 by 3mm in -Y direction (comfortably far from clipping but not enough to center) without moving IMs.

There are many linear combinations of the MC3 spot position and the angle of the beam coming through MC3 that will move the beam on IM4 by 3mm, so I just chose "parallel transport of MC2-MC3 line" (i.e. no angle change of the angle of the beam coming out of MC3), "rotate MC2-MC3 line around MC3" (i.e. no beam displacement on MC3) and something in-between ("rotate around MC2").

See cartoon_IMC_alignment_to_unclip.png (not to scale but the sign of displacement/rotation is correct along the entire path) and IMC_to_unclip_HA12.png (actual calculation). IMC is not the only thing that moves, we can also move IM2, but anyway. In the "parallel transport" case the beam will be move further away from the center of MC2 (remember it was already 3.6+-1mm in -Y direction to start with so the end result will be 6.8+-1mm in -Y direction). OTOH in the "rotation around MC3" case, the beam on MC2 will move by 11mm in +Y direction so the end result will be 11-3.6+-1=7.4+-1mm in +Y direction.

In all cases the beam will likely still hit the IM4_TRANS because the QPD (Excelitas C30845) has a huge 8mm active diameter, but it will likely be completely in one quadrant. So all of these will be bad solution if we believe that the IM4_TRANS position should be close enough.

Note that the "rotation around MC3" case will result in about 1mrad beam angle change on IM4. This needs to be absorbed by IM4 rotation by about 500urad to send the beam to PR2. 

It's also worth noting that IM4-PRM HR distance is almost the same as IM4-IM4_TRANS distance.

What if we fix the beam on IM4_TRANS?

Instead of IMC alignment, now let's think about the beam positions from the end point (IM4_TRANS).

Again, assume that we want to keep the IM4 TRANS beam position. We tried two different IMC alignment, and the beam was clipped on IM4 baffle (HA12) after bringing the beam back to the target IM4 TRANS position.

Moving the beam position on HA12 by 3mm in -X direction without changing the IM4_TRANS position means that we shift the beam position on IM3 by about 8mm. IM3-IM4 path beam angle changes by 4.8mrad counter-clockwise. This is an absolutely huge change. 

PRM should be moved by 2.4mrad, and 8mm on IM3 is already the radius of IFI output baffle (HA6)  so we'll be worrying about clipping there. There seems to be no solution where the beam is far enough from the IM4 baffle (HA12) edge AND the beam is on the same position on IM4_TRANS as in vacuum. 

As far as we assume that IM4_TRANS is trustworthy, it's very likely that the beam was clipping or at least very close to clipping on HA12 in O4.

However, if IM4_TRANS path moved after HAM2 was opened (i.e. somebody bumped something), IM4_TRANS position as of now doesn't mean anything. We have to at least grab and wiggle the steering mirror as well as the QPD for that path to make sure that nothing is loose. (I already did that test for MC2 TRANS, and they didn't move.)

Ryan Short, Tony Sanchez, Sheila

We took beam profiles of the sqz beam in the homodyne path using the Thorlabs M2Ms beamprofiler extension.  It made collecting data for a variety of psams settings much faster than using a scanning slit profiler alone.  

Tips for using this very nice extender kit:

• The visible alignment laser made alignment easy.
• We used the lens LA1461-C for 1064nm, the list of lenses and wavelengths is here: lens list
• make sure that the unit is plugged in, powered on with the power button, and connected to the laptop before you start the software.  Close and re-open the software if "translation stage control" and "M2 set" don't show up for you at the bottom of the "beam settings" window.  Once they show up you just have to go to the M^2 button and hit play to make a measurement.  
• You can get the fit beam parameters by saving a pdf by clicking the button that says "Save test Protokol", you have to hit save twice on the screen where you type a file name and again on the next screen.  "Save Measurement Data and results" gives you all the data, but not the fit beam parameters.  You again have to hit save twice.  
• Sivananda Reddy contacted Thorlabs and posted a diagram of where the reference plane is in the dcc: T2500077

We spent some time refinding the IR beam on the SQZT7 IR PD, documented this in it's own alog so it's easy to search: 90183

We set the profiler as shown in the attached photo.   The flipper mirror is 50.75" from the bottom persicope mirror, a steering mirror is 225mm from that, and the reference plane is 260mm from the steering mirror, so the reference plane is 1.774 meters from the bottom periscope mirror.  Leo Schrader has a helpful list of distances in the google document linked to T2500228.

• In 85282 Leo measured the beam distance from the top to bottom periscope mirrors to be 574mm. 
• The distance from the top of the persicope to the beam diverter was measured to be 84.5" in 61755.   
• In 75749 the distance from the beam diverter to ZM5 is listed as 1183.54mm based on a CAD drawing from Don Griffith. 
• This means the total distance from the reference plane to ZM5 is 5.678 meters.  We have left the profiler and temporary mirrors in place so that we can use them during the upcoming HAM7 vent.  

J. Oberling, R. Crouch, J. Warner, B. Weaver, I. Abouelfettouh

This week we surveyed the position of the components that reside in WBSC2: The BS SUS cage (BSS), the ISI optics table (ISI Stage 2), and the 2 ITM Elliptical Baffles.

BS and the SUS Cage

The first picture shows our FARO survey of points on the BS SUS cage, chiefly along the bottom of the main support structure.  These were surveyed by holding the FARO SMR against the hole being measured; the PolyWorks software handles the compensation from the center of the SMR to the point being measured.  As can be seen, each point is very close in both X and Y axis position, being less than 0.1mm from its nominal location.  The Z axis deviations are larger, but the largest of them is just over 0.25 mm, so every point is well within the positioning specifications used during installation and alignment in 2013.

Line 1 in the picture was created from the first and last survey points and represents the pointing of the BS SUS cage; all angles are reported in degrees.  Some things to note here: I'm using the Acute Angle datum in PolyWorks, which is the angle measured from the closest axis.  For the HR surface normal of the BS, the X Acute Angle is measured from the -X axis, the Y Acute Angle is measured from the +Y axis, and the Z Acute Angle is measured from the +Z axis.  Since Line 1 is roughly perpendicular to the surface normal of the BS HR face, the axes the angles measure from are changed: The X Acute angle is now measured from the +X axis, the Y Acute Angle is still from the +Y axis, and the Z Acute Angle is now from the -Z axis.  In addition, since Line 1 is nominally perpendicular to the BS HR surface normal I would expect the X and Y Acute angles to be swapped (BS X Acute = Line 1 Y Acute; BS Y Acute = Line 1 X Acute), but they aren't exactly.  This appears to be a small error in the CAD model, if we make the assumption that the BS HR surface and the HR side of the BS SUS cage are nominally pointing in the same direction.  This does, however, change the deviations for the X and Y Acute angles for Line 1.  The table below shows what the data for Line 1 should be:

This means the BS SUS cage is yawed 0.0626°, or ~1.09 mrad, in the clockwise (CW) direction when looking from the top down (since Line 1 is closer to the +X axis than it should be).  The Z Acute Angle represents a slight counterclockwise (CCW) roll of the SUS cage, when looking directly at the HR surface of the BS.

To attempt to better locate the BS in the IFO coordinate system, several measurements were taken with a ruler from points on the "Figure 8" section of the BS SUS cage to the BS optic itself.  All measurments except one were done using a scale with 0.5 mm tic marks (so accurate to +/- 0.25 mm).  The 10:00 "Figure 8 face to BS HR face" measurement had to be done using the side of the scale in inches, with 1/32" tic marks (so accurate to +/- 1/64") and then converted to mm (so accurate to +/- 0.4 mm).  The measurements positions are listed like the BS HR surface is a clock, and assumes you are looking directly at the HR surface.  The below table gives those results:

The BS sits decently centered in the Figure 8 portion of the SUS cage, a little bit low and to the +X/+Y side.  I would say not as much horizontally as it looks from the table, given the inherent error with reading the scale (the BS is not wider than its 370.0 mm specification, it's actually 0.15 mm narrower at 369.85 mm).  The pointing implied by this measurement, however, is more than a little alarming.  The 2:00 and 10:00 measurements show a significant yaw of the BS optic w.r.t. the SUS cage, and in the same direction as the yaw of the SUS cage as measured by the FARO.  There is ~320.0 mm between the 2:00 and 10:00 positions on the BS, so that 1.45 mm difference in depth is a 4.53 mrad CW yaw.  When added to the CW yaw of the SUS cage, this measurement shows that the BS optic is yawed 5.62 mrad CW from its nominal yaw.  Even assuming the errors fall in our favor (so the 2:00 at 25.0 mm and the 10:00 at 25.8 mm), that's still a 3.59 mrad CW yaw (2.5 mrad BS and 1.09 mrad SUS cage).  In addition, the 6:00 measurement implies a significant downward pitch of potentially several mrad, although with no way to measure the top of the optic we can't actually measure it.  I have to be honest, I'm having a very hard time believing this measurement; we will revisit this once the BS cartridge has been moved to the test stand, where we have a better field of view for the FARO, more room to work and much better lighting around the BS, and can take direct measurements of the BS position and pointing using a total station and laser autocollimator (although there is no guarantee that the optic will be pointing in exactly the same direction after being craned across the LVEA).  More to come on this.

ISI Optics Table

The second attachment shows the ISI positions as measured by the FARO.  I've corrected the Z axis positions for the length of the rod we use to hang the SMR from the ISI so they give a better idea of the Z axis position.  Not much can be said here, as LLO discovered that while these rods are good for measuring the Z axis position, they are not at all good at measuring X and Y.  This makes sense as they were designed to be accurate in length and only length, so there's no guarantee that X and Y are repeatable.  We plan on measuring the X and Y errors of this particular set of rods in the coming days (align to a table with a known hole pattern, attach the rod and measure with the FARO, repeat multiple times to see how the X and Y positions change).  For now, we can say that the ISI is lower on the -X side vs the +X side, and lower on the +Y side vs the -Y side.  I'm not alarmed by the deviations in Z axis position, as this ISI was supposed to be lower by ~2.5 mm (to place the BS in proper Z axis position, since it's lower in the IFO coordinate system but the SUS is the same length as the QUADs), but this was never captured in the CAD files.

ITM Elliptical Baffles

The final four attachments show our survey of both ITM elliptical baffles.  Our view of the baffles and available fiducials to take measurements from were both limited, but we can say a few things.

ITMx Elliptical Baffle

We were able to get two points along the +Y bottom edge of the baffle, a single point along the +Y top edge, and single point near the center of the -X bottom edge of the baffle.  From this I made a couple of planes that represent the +Y and bottom sides of the baffle and are shown in the third and fourth attachments; I, J, and K are the direction cosines of the surface normal of the plane, while the listed angles are the angle from the surface normal to the +X, +Y, and +Z axes. Interestingly, the point on the top edge looks very well aligned, within 1.0 mm all around, while the points along the bottom of the baffle are all low by several mm.  In addition, there appears to be a significant upward pitch to the baffle.  Jim did note that when attaching the transport bracket he had to push the baffle in the +X direction to clear ~0.5 mm at the point where the bracket attaches to the suspended portion of the baffle.  This point is roughly 476 mm away from the baffle's suspension blade, so this is an ~1.05 mrad angle.  Applying this same angle along the bottom of the baffle box gives an ~ -0.33 mm Z axis move of that bottom -X edge of the baffle, so this does not account for the measured deviation.  In addition to the pitch, the bottom plane also shows a large roll (CCW when looking at the ITMx in WBSC3), while the side plane shows a large yaw (CCW when looking from the top down).  We know these baffle panels aren't exactly straight, so it's hard to say if this significant pointing is also present on the elliptical hole of the baffle (we couldn't see it, so we couldn't measure it directly).

ITMy Elliptical Baffle

Similar to the ITMx baffle, we were only able to get a handful of points along the -X side and the bottom of the baffle.  I made planes from these points representing the -X side and the bottom of the baffle (fifth and sixth attachments).  As seen with the ITMx baffle, the points along the top of the baffle all look good while the points on the bottom are too low by several mm.  There is a significant upward pitch to this baffle as well, as well as a large roll (CCW when looking at ITMy in WBSC1) and yaw (CCW when looking from the top down), although none are as large those as seen on the ITMx elliptical baffle.  Again, we could not see the elliptical hole in the baffle to measure it, so we can't say if this pointing is an artifact of the panels or also present on the actual baffle portion of the baffle.

This completes our in-chamber measurements of the WBSC2 cartridge assembly, and closes LHO WP 13171.

I also want to note, Ryan and I also preformed some in-chamber FARO measurements in WHAM3 (ISI, MC2 SUS cage, PR2 SUS cage, MC2 and PR2 baffles) on April 10th; I will post those as soon as I get a chance to process the data in PolyWorks.