FAMIS 63899 

No major events of note; things looking very stable recently.

In preparation for testing out the BOSEMs on the BBSS, I've updated the OSEM2EUL and EUL2OSEM matrix values from the suspension projection values for the BSFM's geometry to projection values from the BBSS's geometry.

OSEM2EUL

before (BSFM projections), after (BBSS projections)

EUL2OSEM

before (BSFM projections), after (BBSS projections)

TITLE: 05/18 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: 12mph Gusts, 6mph 3min avg
    Primary useism: 0.03 μm/s
    Secondary useism: 0.15 μm/s 
QUICK SUMMARY: No alarms over the weekend, temperatures looking normal, dust counts low as well. The same 31 channels are disconnected from the EDC since the CS HEPI pump controller is still down.

Likely continuing with alignment work in HAM2 today following the ISS array replacement.

TJ and I cleaned the BSC2 aluminum floor, the bottom of the chamber below that, feedthrough nozzles, support tubes and their nozzles (see figure for photo of cleaning and some of the stuff we found). The particulate level while walking around gently did not change significantly from before to after the cleaning (see table below). This and the other cleaning experiments reported in the table suggest that, at the current state of cleanliness,  the dominant source of suspended particulate is the people and the things we bring in rather than dust that we stir up by moving around. 

The dust counts generally returned to low levels a minute or two after the activities in the table.

Just as patting clothes produces more dust, we found that rapid movements produce more dust in the chamber than slow movements. The linked video shows the movement speed and the wiping speed that produced the lower levels in the table below: slow chamber speed. 

Recommendations:

1. The chambers are currently clean enough that general cleaning is probably counterproductive.

2. Move slowly when possible. This can reduce the particulate suspended from your bunny suit by an order of magnitude.

* Particle counts are aproximate averages, mostly of 1 minute samples. Repeats suggested that differences in the table of a factor of two or greater are significant. Quiet controls were taken in between reported measurements to ensure that measured levels were not significantly affected by previous activities.  Monitor: Met One  GT-521S laser particle counter 

TJ and Robert

One problem solved, two problems found.

Clipping on IFO REFL baffle is gone.

The problem of IFO REFL beam clipping by the last IFO REFL baffle in HAM2 (see alog 90251, especially this picture) seems to have been caused by a huge PRM change in the PRM alignment sliders made on Monday May/11/2026 past 1700 local time (that none of us knew/remembered/understood).

Once Sheila reverted PRM back to March/2026 alignment, changing the IFO REFL beam path (but not the alignment into ISS path), IFO REFL was not clipped any more even though it looked low on the baffle (IFOREFL_baffle.mp4). LSC and ASC REFL sensors on HAM1 ISI saw the flashes right away without any adjustment of RMs, and the flash peaks were already reasonable. According to Sheila,  compaing to a time when DRMI was acquiring in November:

• 2W into IMC vs 0.18W into JAC now (9%, the power into IMC is less than that due to extra losses expected for JAC)
• REFL A nsum 4000 counts then, 218 now (5%)
• REFL B nsum 3400 then, 204 now (6%)

All of these were a good sign.

Forward-going beam into the IM4 is clipped by the baffle in front of IM4, and the IFO REFL beam is clipped by the baffle at the -Y edge of the IFI.

Unfortunately I've found that there were two other clipping points that I must have missed yesterday using IR viewer. See clipping.png, sorry for a blurry through-IR-viewer picture shot from the distance. Go back to HAM2layout_annotated2.png to figure out which baffle is what.

There's a baffle in front of IM4 between IM4 and IM3, and the forward-going beam is slightly clipped at the +X edge of that baffle.

Also the IFO REFL beam is clipped by the baffle installed at the -Y edge of the IFI. I know this is IFO REFL because the bright spot goes away when I block the beam on PRM by a sheet of aluminum. I cannot quite tell from the picture which edge of the baffle is clipping, but I think it's also +X edge.

In the past, when PRM spot position was measured with full IFO, it was like a mm off according to Sheila, so it's hard to imagine that the beam was clipping on the baffle in front of IM4.

Changing IMC alignment (trial 1, didn't fix clipping).

We decided to back off the changes we've made  for MC1, 2 and 3 since Monday and revert back to in-vac March alignment. If we have to make a huge adjustment to JM3 to follow the IMC, maybe the beam coming from JM3 is suspect (which means that the MC2 trans path is somehow suspect too).

Before I did anything, the starting point was captured in alignment_2026-05-15_16-14-21.png.

MC1/2/3 was reverted just based on slider values and not using OSEM readings as per alignment_2026-03-18.png.

Then JM3 was adjusted in PIT and YAW to give the maximum transmission measured in IM4_TRANS_NSUM. Actually I didn't move JM3 as much as I expected.

That alone couldn't recover a good 00 mode flashing so I moved MC2 and MC3 to follow the input beam.  MC2 moved back closer to the position this morning.

After that I felt as if it was somehow easier to optimize further using MC1 as well as MC3, thinking that it would be a minor adjustment but somehow ended up moving MC1 by a large amount after iterations.

My end point is captured in alignment_202605151726_sliders.png.

Without IM3 and IM2, the beam was still on IM4_TRANS as well as ISS QPD, the flashes were good, so I looked at the clipping on the baffle in front of IM4 as well as the baffle at the -Y edge of the IFI, and they were still there. IFO REFL baffle was still not clipping.

Will have to think about what these all mean.

Ibrahim, Betsy, Oli

Today, we installed BBS01 into the BBSS successfully. 

BBS01 was on a table. BBSS was on the aluma lift. We picked BBS01 using the ERGO arm and slowly came into the optic. In this process, we:

• Removed the EQ stops and replaced them with the glass tips
• Ensured that the gold wire was held correctly about the lower structure barrell
• Made contact between the gold wire and the grooves of the prisms
• Backed the glass tip EQ stops in to contact, securing and locking the whole suspension (M1 and M2 were already locked)
• Installed the BBSS face shields
• Practiced a lift of how it would go up into the test stand
• Placed teflon pads between the lift arms and the BBSS 45 degree lifting bars - LLO did the same (alog 80802) - this helps with fine structure adjustment when below the ISI
• Covered the BBSS on the lift in prep for test stand install (IAS needs time with the ISI to get exact positions in XY for where BBSS will sit).

On top of pictures below, 2 videos:

• Pushing BBS01 In
• ERGO Arm Sighting and Adjustment

J. Kissel 

SPI Wiring Diagram: D2400111-v6
In-chamber in-vac cable routing: In-vac Cable Routing Plan from G2401479-v3

I never aLOGged our choice of cable-table bracket floor assignment down when we originally assembled and signal-checked the D2400107-v4, so during disassembly in prep for upgrade to D2400107-v5 (LHO:90225) I took the time to write down the cable routing, cable serial number assignment, and cable table bracket (CBT) floor assignment:

Path       PD Name         PD SN          Duopus      D9 CBT Name / Floor     Quadrapus    D25 CBT Name / Floor 
                      |----------D2600001--------|  
                      D1600083 Type 2     D2400341    D2000492                D2400343     D2000492 
    
                                                                              S2500512
IFO REF    A/B        S2401096/S2401095   S2500516    CBT 2 / 2nd of 2        cable E      CBT 1 / 1st of 2   
IFO MEAS   A/B        S2401097/S2401098   S2500514    CBT 2 / 1st of 2        cable D      CBT 1 / 1st of 2
FBR PWR    REF/MEAS   S2401094/S2401093   S2500515    CBT 3 / 2nd of 2        cable C      CBT 1 / 1st of 2

                           PD SN          Monopus 
                      |----------D2600002--------|
                      D1600083 Type 3     D2400340

OL ISIK    QPD B      S2401091            S2500518    CBT 3 / 1st of 2        cable B      CBT 1 / 1st of 2

First and Second of the attached pictures are of the CBT 2 cable routing. I needed two pictures because the D9 end's two-part backshell of IFO REF cable was assembled with its serial number stamped on one side of one part, and the other side of the other part. C'est la vie.

Third picture is of CBT 3's cable routing.

The 2x D9 CBT assemblies (since the "type" we've assembled is not explicitly drawn in D2000492) are 
    - QTY 1x D2000519 baseplate
    - QTY 1x D2000520 "Type 2" two-floor uprights, with
    - QTY 2x D2200443 D9 adapters,
    - QTY 2x 1/4"-20 x 0.625" L captive SHCS (95966A512) for securing to the HAM table (rather than the 3/8"-16 captive SHCS that are used to secure to the BSC tables)
    - QTY 2x #6-32 x 0.375"L SHCS (92200A146) for securing the baseplate to the upright
    - QTY 2x per D9 adapter (4x total) #4-40 x 0.224"L ("2D"; 1185-04EN224) nitronic 60 helicoils for each of the upright holes
    - QTY 2x per D9 adapter (4x total) #4-40 x 0.5"L captive SHCS (95966A140) for securing the adapters to the upright

For the single D25 2-floor CBT that holds the D25 ends of the PD and picomotor quadrapuses, we used the standard D2000492 Type 2 configuration.

We started with yesterday's alignment. I checked flashes in ISS array PDs and didn't like that the balances between them were very much different from how they were when IMC was locked back in March.

Then we started changing IM2 and IM3 to see if we can get back, but I was appalled that the flashes became stronger and stronger on array PDs as we aligned, which probably means that the beam was almost falling off of the PDs when we started. 

That shouldn't have stopped us because we don't know where the beam was on the array PDs when MC was locked (people gave up optimizing that path because things didn't make sense), it could have been falling off of the diode (because each diode is 2mm,  QPD is 3mm, the beam size is ~250um or so, and the beam was almost in one quadrant of the QPD). But I started thinking about many what-ifs and wasted time.

After all, since IM4 TRANS and ISS array QPD are both reasonably close to March 2026 position, we know that the beam position as well as angle of the beam injected into ISS path from IM4 are already close to those when IMC was good in vacuum.

What we should do is this:

• Revert back to Monday IM2/IM3 alignment. Confirm that the IM4 trans position as well as ISS array QPD position are OK.
• Check flashes in 2nd loop inloop and out-of-loop sum. Recheck if at least one of them is comparable to when IMC was locked back in March, taking into account the power difference, even though Sheila checked it yesterday. At this point, we'll have established again that the position and the angle of the beam coming into the ISS path are reasonable.
• Check that the beam in ISS path is nowhere near being clipped by baffles and ISS array cover and the elevator aperture of the ISS array. Don't fix clipping right away, do it after swapping the array because we'll have to move pico mirrors anyway.
• Swap the array. There's no assurance that the beam will be on the QPD right away but that's OK. We can move the unit on the spacer if that helps. Go as close as you can, then start using the two pico steering mirrors. Use the array input aperture to aid the process.
• Once you see the beam on the QPD, continue to center the QPD, fix clipping, not necessarily in this order.
• Check the flash height of array PDs as well as QPD, see if things makes sense.

Other things to note:

This is not required for the alignment but it's helpful to know how much we can move the beam on QPD. In an unlikely event where we somehow lose the beam in vacuum on the array QPD after IMC is locked, we might be able to scan IM3/IM2 to regain the beam on QPD, and slowly move IM3/IM2 back to the nominal position while pico-ing so the beam isn't lost on the QPD. If the beam is not clipped, the beam displacement on the QPD is ~3mm per 1mrad of IM3 rotation using parameters collected from various documents, see attached script.

The same script shows you that the Gouy phase separation between two pico mirrors is 10 degrees (if we use the beam parameter in Matt Heintze's alog 12537, which was probably obtained by the measurement of the bypassed beam) or about 20 degrees (if we use IMC eigenmode parameter propagated to the ISS path using D1200693).

Another thing is, if we believe the design eigenmode number rather than the measured bypassed beam in Matt's alog, the beam waist will be smaller and at about 20cm upstream of the PDs. The beam size on the PDs is about twice as large as it should be (470um rather than 250um). I cannot measure the beamsize of the flashes so we won't do anything, but that's something to remember. If IM3 has enough actuation range, we can later lock the IMC, scan the beam across the PD until the beam falls off, see how sharp the fall-off is, and use the diameter of the PD (3mm) to determine the size of the beam. Maybe a good project for a fellow.