Robert, Ibrahim, Anamaria
We finished alignment of the CP cage baffle on ITMX, which was the last item to do regarding cage baffles. The panels are locked so they can now be removed and replaced while retaining the alignment.
Both ITMs have the (new) face shield on. ITMY suspension is unlocked and ITMX is locked.
Begum, Ryosuke, Camilla, Madi
Summary: Were able to retroflect the beam off FC1 (when placed at O4 sliders) with ZM2 and ZM3 but the beam height is incorrect, as expected, VOPO optics will need to be moved to fix this.
Attached alignment for good alignment towards IFO, on ZM4 iris and SQZT7 IR PD irises. Both when OPOs is unlcoked and locked. When OPOS is locked beam doesn't go though closed irirses so isn't perfectly aligned but it is close enough.
Our Friday's alignment for FC retrorefection (with non-ideal) beam height:
With the new cage baffles installed on ITMY, Anamaria and I went in to hammer the cage. The suspension was unlocked and the ISI locked. The accelerometer was mounted on the cross member between the L3 and L2 stages (photo) with the accelerometer axes X,Y,Z = IFO -Z,Y,X. All plots have the accelerometer axes plotted. Measurement numbers are just for my own reference. LLO's results for their ITMs can be referenced in LLOalog81300.
| Hit Description | Photo | Plot | |
| Meas 2 | on top crossmember hitting in -Z IFO | Attachment 5 | Attachment 1 |
| Meas 4 | Hitting from side of cage -X IFO | Attachment 6 | Attachment 2 |
| Meas 5 | +Y IFO on the TM side of the cage on the baffle bracket | Attachment 7 | Attachment 3 |
| Meas 6 | +Y IFO at the bottom of the cage | Attachment 8 | Attachment 4 |
Longitudinal first peak 57.5Hz
Transverse first peak 64Hz, with a second nearby at 67.5Hz
TITLE: 06/05 Day Shift: 1430-2330 UTC (0730-1630 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY:
ISS PD Array alignment was most of the day and there was several activities in BSC1+2+3, as well as work in the CRS lab, @HAM7, and brief SPI feedthru work at HAM3
LOG:
J. Kissel, J. Warner, J. Wright Jim, Jennie, and I started working on converting the HAM3 D5 feedthru from D1002874-v9 to D1002874-v10. This feedthru (in -v9) serves "corner 2" of the HAM2 ISI. We didn't finish, but here's how far we got (all in the -X / -Y / -Z corner of the chamber where the D5 flange is): - Powered OFF all HAM3 ISI sensor (via ISI interface) and actuators (via coil drive) in the SEI-C2 rack. - Disconnected the in-air connections (2x 3W3 actuator cables, 2x BNC CPS cables, 1x GS13 D25 cable) to the feedthru. (easy, by hand / thumbscrew) - Removed all strain-relief cylinders (easy, simply hose clamped) - Disconnected as many in-vac connections as was easy (Horz CPS BNC, Both 3W3 actuator cables) - Removed the dual D4-2B 4.5" flange, wrapped and tagged it with the copper gasket on to protect the knife edge - Covered the exterior / air-side in foil, mindful of the knife edge. - Restored C3 parachute I could not easily thumb-and-finger off the Vert CPS BNC (Jim says they're notoriously difficult on the clean side). I could not find the right allen key size to unscrew the GS13 D25 connector. We'll pick it up on Monday next week (2026-06-08). Pictures attached: BEFORE AIR SIDE BEFORE VAC SIDE END-OF-DAY STATUS
J. Kissel, S. Koehlenbeck, J. Wright D2400144 D2400145 For those who haven't been following closely, the SPI pathfinder was chasing what we *thought* were alignment issues -- during which we pointed our finger at the (Newport) pico-motor actuated (Siskiyou) IXM100 1" mount assemblies (both IXM100.C2 right-handed and IXM100.C2L left-handed). While this ended up *not* being the problem, we still took action on these mounts. This is the summary of that activity -- we figure worth a separate aLOG because LIGO has been using these pico-motor actuated IXM100 assemblies for a long time, and we're surprised that no one has raised this as an issue before. The issue: (repeat of what's burried in LHO:90382) - "Out of the box" the Siskiyou IXM100 mount has two carbide plates that kinematically receive the manual alignment pushers on the moveable front-plate (item 1) of the mount. See item 7 in D1100362. - Notice that v-grooved carbide plate, item 7, is called out twice, one for pitch and one for yaw, just installed in a different orientation such that the v faces the pitch drive and the flat faces the yaw drive. - This means the pitch and yaw manual drive pusher screws must be at different depths to achieve the "nominal" position of movable mounting plate. Not my favorite, but it's a non-issue with system "out-of-the-box" because the outer-diameter of 1/4-100 alignment screws clears the inner diameter of the housing carved out for the carbide plate in the movable mount plate. - HOWEVER this discrepant drive depth matters when we instead drive the plate with the Newport 830X-UHV, because its stopper nut (see it called out in 830X-UHV_RC_revA.pdf from E1000197) *sometimes* does NOT clear the moveable plate. And this *only* happens in the pitch drive, because Siskiyou didn't need to worry about the different depth of drive. So, you get varying results of how close the stopper nut is to the movable plate depending on how it was fixed by the Newport manufacturer, potentially shorting the design-intended, kinematic, ball-to-v-groove connection. If it's the stopper nut making contact then you get circular-plate-to-flat-plate drive which can rock-around and is poorly-constrained enough to cause some unwanted cross-coupling to yaw drive. See pictures of "BEFORE" of the two examples we were suspicious of: 2026-05-29_M_B4_PicoPitch_BEFORE.jpg 2026-05-29_M_B4_PicoPitch_BEFORE_02.jpg 2026-05-20_M_M2_PicoPitch_BEFORE.jpg 2026-05-20_M_M2_PicoPitch_BEFORE_02.jpg It was recommended to us to "just move the stopper nut." Like I mentioned in LHO:90382, this was *not* a thing meant to be done often. With an allen key holding the pusher screw in place from the back, it required a great deal of clamping and twisting with pliers to get the nut to budge. Plus, given the 100 TPI thread, you gotta turn it a lot in order to get the nut to back off even 1/4 [in] (a few [mm]). See pictures of "cranking": 2026-06-02_PicomotorScience_StopperNut_Cranking_01.jpg 2026-06-02_PicomotorScience_StopperNut_Cranking_02.jpg 2026-06-02_PicomotorScience_StopperNut_Cranking_03.jpg 2026-06-02_PicomotorScience_StopperNut_Cranking_AFTER.jpg Once done, you can see an obvious and clear gap, see pictures of "AFTER:" 2026-06-02_ISIKTransceiver_M_M1_PicoPitch_AFTER.jpg 2026-06-02_ISIKTransceiver_M_B4_PicoPitch_AFTER.jpg 2026-06-02_ISIKTransceiver_M_M2_PicoPitch_AFTER.jpg
J. Freed, S. Koehlenbeck, J. Kissel,
(Belated post)
Wednesday we continued from 90352, We installed the full rack for SPI in SUS R2 and made all connection between different SUS R2 racks as well as connections from TIA to DAC. (Front:IMG_6377.jpeg)(Back:IMG_6388.jpeg). As well as, hooked up to all the required power supplies. Still missing some connections namely SUS R2 to chamber connections
The RF power measurement going out from the 2W amp to the SPI prep was measured to be 31.6 dBm for both outputs of the 2W amp (after the amp warmed up).
This was measured by using the on site power mon w/ small power probe (Exact make and model will be added later). The site has a large power probe (the HP 8484A) but from 89523 it was found to have some strange nonlinearities. As such, the small probe was prefered for this test. Since the probe only has a 20dBm max power limit, 2x 10dBm attenuators (UNAT-10a) were used to lower the power to be able to be measured. Of course the UNATs have a 33dBm limit so special care was used to make sure that limit was not reached. This set up was calibrated by using a 0dBm signal which the probe measured as 0.1dBm. attaching the 2 attenuators the same signal read -20.0dBm (a 20.1dB difference). Then I measured the 2 ports which read 11.8dBm for the Meas output and 11.7dBm for the Ref output. Once the amp warmed up (~20 minutes of waiting with it on) these values both fell to 11.5dBm. Adding back that 20.1dB, this leaves both port with the expected output of 31.6dBm. With an error of +/-0.1dBm.
This value is 0.4dBm lower than the optics lab measurement with the larger probe but is a more precise measurement with less error.
The SPI wiring diagram D2400111 is labeled wrong. Namely it says Output 2 of 2W amp connects to the meas port of SPI prep. And Out 1 of of 2W amp connects to the ref port of SPI prep. This is wrong. Out 1 of of 2W amp connects to the meas port of SPI prep (I physically labeled SPI_RFDist_008) and Out 2 of of 2W amp connects to the ref port of SPI prep (I physically labeled SPI_RFDist_009)
We also installed 3 BNC cables for the monitor channels of SPI Prep. These are not labeled in the wiring diagram but Jeff physically labeled them as SPI_LPMON_M1_PD, SPI_LPMON_M2_RFMEAS, and SPI_LPMON_M3_RFREF. Which monitor: the PD inside SPI prep, the RF power for the 80 MHz Meas signal, and the RF power for the 80- MHz Ref signal respectively.
J. Kissel (Belated aLOG) After the great success on Tuesday 2026-06-02 solving the mystery with the MEAS IFO's efficiency drift (LHO:90455), we declared victory and spent the morning packing up all of the clean assembly to be ready for install. We - Weighed the mass of what components will be suspended on Stage 1 of the HAM3 ISI (see LHO:90504) - Packed up the optical fiber feedthrus (see Attached Pic #1) - Packed up the ISIK Transceiver and its in-vac cabling on a roll-able clean cart quadruple wrapped in foil (see Attached Pic #1) - Packed up the two D25 to D25 pico-motor and PD cables that span from Cable-Table-Bracket #3 to the HAM3-D6 feedthrough. - Powered down, disconnected, and packed up . the laser prep chassis (see bottom of Attached Pic #3) . the transimpedance amplifiers (no pic) . the commercial RF source Keysight 33600A (no pic). . all in-air cabling, including mock-feedthrough The fiber-coupled NPRO is still set up, but the laser is shuttered and key'ed off. Thank you optics lab, and good luck trail-blazing to you, SPI pathfinder!
J. Kissel, S. Koehlenbeck Here's the mass of the SPI pathfinder's ISIK transceiver that will be suspended on HAM3. 10.958 [kg] :: Fully assembled ISIK Transceiver (D2400107) - no installation handles - no baffle bracketry - sensor/actuator cabling draped to the side 0.898 [kg] :: Fully assembled portion of in-vac cabling that will be suspended on Stage 1 of HAM3 ISI - includes cable table brackets - excludes QTY 2x D25 to D25 signal bus cables that span ST1 to ST0 to Feedthru. 0.703 [kg] :: Fully assembled portion of in-vac fiber optic cabling that will be suspended on Stage 1 of HAM3 ISI - 0.570 [kg] :: QTY 2x will be suspended so expect 2x0.285 = 0.570 [kg] . 0.285 [kg] :: QTY 1x Fiber spool (what was actually measured, rather than two) . Most of the optical fiber, plus wont-be-there fiber mating sleeve and cap - 0.133 [kg] :: QTY 2x Fiber spool assembly feet and installation hardware: 12.599 [kg] :: Total suspended mass. All this mass will be on the -X side wall of the ISI, below the optical table, as shown in D2400103. We have not measured the mass of any component of the ISIK shroud assembly D2400106.
J. Kissel, T. Shaffer, M. Robinson While in HAM2 doing BnK hammering (LHO:90493), Mitch asked us to note the serial numbers of all parts of HAM2 ISI Table Baffle Assembly (D1700335). Location Drawing Serial Number +Y Assembly Baffle D1700263-v1 004 +Y Bracket D1700264-v2 020 -Y Bracket D1700264-v2 014 Middle Assembly Baffle D2600042-v1 001 +Y Bracket D1700264-v2 013 -Y Bracket D1700264-v2 015 -Y Assembly Baffle D1700263-v1 006 +Y Bracket D1700264-v2 022 -Y Bracket D1700264-v2 017 Happy ICS'ing! (Will post picture proof in due time.)
The middle, center baffle assembly was installed/updated on 2026-05-26; LHO:90335
TITLE: 06/05 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: 6mph Gusts, 3mph 3min avg
Primary useism: 0.05 μm/s
Secondary useism: 0.14 μm/s
QUICK SUMMARY:
ISS alignment final steps, BSC in-chamber of activities at BSC1+2, HAM3 SPI, viewport inspection are among activies on the docket today.
Alexandra, Shoshana, Arnaud, Fil, Dean (remote)
Today we completed the balancing of the CRS with a period of 61s (or 16.4mHz, which is our target frequency), aligned and tuned the HOQIs (with >75% fringe visibility) and connecterized the picomotor to the mighty mouse connector. Tomorrow, after verifying the balancing and alignments have not changed, we will mount the HOQIs to the CRS, which will complete this first assembly.
In detail :
Note1: We did break a set of flexures during balancing today (SN 18 and 11)
Note2: We could not get good fringe visibility on a 3rd HOQI (max 60%) we tested. We will have to get back to this one.
Note3: The Right HOQI has a PD wire that seem to have been pinched during assembly (see last photo). This doesn't seem to be an issue, we will just have to be careful when routing that it doesn't touch the baseplate.
Belated, as usual.
We continued HAM2/3/1 alignment. Things are making more sense now after realizing that RM1 and RM2 slider polarity was wrong but we're still finding things.
1st attempt: We rotated IM1 to relieve RM2 YAW (IM1 y -987->-687 i.e. +300 from Tuesday value), aligned PRM so the beam retroreflects (but didn't touch up other IMs in the interest of time). After some confusion it worked and we were able to center REFL ASC sensors without railing RM2. Happy. (See ASCREFL_centered_RMs_dont_rail.png. If you do the math using flash peaks, REFL_A PIT=0.034, YAW=0.013, REFL_B PIT=-0.0097, YAW= -0.017, so it was very good.)
2nd attempt: Encouraged, we proceeded to center the beam on the IFI output baffle using IM2, steer the beam to the nominal beam position in front of PRM using IM3, steer the beam to the nominal position in front of PR2 using IM4 (which moves the beam position on PRM by a small amount but we didn't bother to iterate), and finally aligned the PRM so the retroreflection is restored. We were able to center REFL ASC sensors without railing RM2. Happy again. (eod.png, REFL_A P= 0.034, Y=-0.009, REFL_B P=-0.023, Y=-0.022.)
We looked at the beam position on IFO REFL baffle and it was off in YAW, so we changed the baffle position slightly in +Y direction.
We didn't change IM1-IM2 line, which means that the alignment into HAM1 should not have changed assuming that the PRM was retroreflecting, but the YAW offset necessary for RM2 to center the ASC sensors in the 1st and 2nd attempt were very much different.
| all numbers are in urad |
1st attempt (PRM P, Y = -1165, 320) |
2nd attempt (PRM P, Y= -1165, -300) |
2nd [P,Y] - 1st [P,Y] |
| RM1 [P, Y] | [-243, -45.3] | [-257, -114] | [-14, -68.7] |
| RM2 [P, Y] | [930, -989] | [950, -1489] | [20, -500] |
In the 2nd attempt, RM2 Y offset changed by negative 500urad and the DAC output of two of the RM2 coils reached ~107 million, which is about 80% of the DAC range. That's closer than I'd be comfortable with before closing down the chamber.
It turns out that this is consistent with our retroreflection accuracy which I claimed to be "like +-50urad" in PRM rotation (not the beam rotation) in alog 90451.
Equivalent of positive PRM rotation of 50urad in YAW is replicated by the combination of physical negative 55urad for RM1 and physical negative 380urad for RM2 (note that the sliders for RMs as of now has the opposite sign as the physical rotation).
If retroreflection is off in terms of PRM YAW rotation by +-50urad, when the REFL ASC sensors are centered, RM2 YAW would be off by +-380urad from what would be required to center the beam that is truly retroreflecting. See attached script. 500urad difference between two attempts is consistent with that.
On top of that, it's possible that +-50urad error estimate is too optimistic. We set the PRM angle by centering an iris (placed between IFI input and IFI HWP) to the forward going beam and centering the back propagating beam on the back of the iris. The basis for the accuracy is that we could start seeing how the circumference of the back of the iris is unevenly illuminated by the back-propagating beam when we gave the PRM 50urad offset, but the beam is always moving in YAW and sometimes rather slowly, so we have to eyeball the average beam position.
We don't know if the 2nd attempt was closer to the true retroreflection or, for that matter, if the true retroreflection is "on the other side of" the 2nd attempt relative to the 1st.
As such, it's prudent to relieve RM2 YAW offset further.
Relieve RM2 further by giving IM1 a positive 300urad YAW rotation. IM2, IM3, IM4 and PRM should be readjusted accordingly.
IM1 YAW offset hasn't changed much in the past 2 years except for this week, and we'll go back to that neighborhood. Even though this means that the beam on IFI input baffle will be off-centered (probably it's been like that for years), I'm absolutely sure that the forward-going beam won't be clipped, I'm also quite sure that the clipping-like thing of the IFO REFL beam on the IFI input baffle won't come back as far as PRM is retro-reflecting.
We might have to move the IFO refl baffle again.
We WILL move the IM4 baffle because whenever the beam is aligned to the nominal position in front of PRM the beam is too close to the +X edge of the baffle.
(Betsy, Randy, Jim, Tyler, Travis, Jordan, Gerardo, Mitchell, Corey, Ibrahim, Danny on watch)
Ibrahim and crew prepped the BBSS yesterday for flight.
This morning Jim and I finished cable routing and stowing and made some final pre-flight preps.
This afternoon, we successfully flew the BSC2 Cartridge from the West Bay Test Stand to the BSC2 chamber and installed in onto the support tubes via the dome.
Tyler, Travis, Jordan, Corey, Jim in suits at the Test Stand for lift off
Randy on the Crane controls
Mitchell, Gerardo, Betsy in support
Jim and Ibrahim in the chamber for the lowering, alignment and support tube bolt attachments
Danny on Safety watch
More pictures to follow, but attaching a good one of the LVEA perspective actross the West bay and of Danny monitoring the flight.
Well done all, big job complete. Now tune-up, align and close! Easy button.
When I hammered the below table "beard" baffle on May 26 (alog90335), something wasn't correct with the way I saved the data or my configuration or something else. Either way, Jeff and went in today and hit that as well as the SPI ISIJ assembly with and without the cylindrical shroud (D2500030). Preliminary results are looking much better, so I'll clean those up and post them soon with a whole writeup.
J Kissel, T Shaffer
All plots are in the accelerometer axis as defined below for each test. The measurement numbers were just for my own organization within the B&K software.
We did this in two stages, one set with the D2500030 cylindrical shroud and one set without. The accelerometer was mounted on a bolt hole below the ISIJ on the HAM face (photo).
| Hit location (on shroud or reflector) | With Shroud | Without | Comparison plots |
| -Y IFO (+Y acc) | Meas 5 | Meas 9 | Attachment 1 |
| +Z IFO (-Z acc) | Meas 6 | Meas 10 | Attachment 2 |
| -X IFO (+X acc) | Meas 8 | Meas 11 | Attachment 3 |
The shroud has clear resonant peaks at 137, 196, 314Hz. It was ultimately decided to leave this piece off for now.
Measuring the central below table baffle (D2600042) with the accelerometer mounted on the L bracket (D1700264) on the outermost bolt hole (photo). The accelerometer axis X,Y,Z = IFO -Z,Y,X.
Meas 1 - First hit IFO +X (+Z acc) bottom of L bracket - attachment 4
Meas 2 - hit in -Y IFO (-Y acc) on L bracket - attachment 5
Meas 3 - hit in +Z IFO (-X acc) L bracket bottom. Note that the bracket is tilted in the IFO -X direction. - attachment 6
There is a small peak at 87Hz.
Here's video evidence of the resonance -- see https://www.youtube.com/watch?v=bgA-cGWJSbg. (Video is sadly too large for posting to aLOG.)
(Jordan V., Gerardo M.)
We have noticed that the dew point at the dryer towers has been increasing since opening to HAM7 and or related to power glitch last Saturday, we are still looking into it.
We have had a constant dew point at the dryer towers of -72 oC, and now we are at -57 oC, because of those numbers we ran a short test, once work was finished for the day in-chamber, we stopped the purge air to the LVEA to see what the effect was on the drying tower's dew point, it changed but very slow, we started at -57 oC and after 20 minutes we ended up at -59 oC, and we noted that the right tower may be in trouble since the dew point did not improved while this tower "works", the dew point instead went up by the one degree, erasing the improvement of the left tower. We will look more into it.
To complete the test we took a dew point measurement at the point of use in the LVEA, and we got a -40.7oC, getting close to a bad dew point, and remember this is while no in-chamber work is going on, so please mind those C3 soft covers on chamber doors, thank you.
Today I power cycled the dryer towers for the purge air system, I did this to shut it off in a controlled manner instead of a power glitch/outage, like the ones from last Saturday, see entry here, and then restarted the unit back up, the dew point at the dryer towers improved by 4 degrees.
Also, I took a couple of dew point measurements at different places:
In conclusion, despite the great demand of purge air, the dew point still is good, but please don't waste it, if you can please keep those C3 door covers closed. Thank you!
Today started with removal of the HAM7 +X and -Y doors, WP 13283. These were already on 4 bolts/piece, so removal was relatively quick. Nothing to note other than the usual O-ring sticking business. The 2x 12" CF blanks on the +Y door were also removed for ISI locker access. Since the final cleaning happened ~1 hour from door removal, particle counts were very minimally elevated, 40 @ 0.3um and 20 @ 0.5um (see pic).
We then moved on to the X-beamtube manifold vent work, WP 13284. The X-manifold turbo pump was valved out. We then cycled GV7 open, then hard closed again. The GV opened at 10 psi, and hard closed at 20 psi, so we believe the piston O-ring replacement is working well. Then, the X-manifold vent was started. After burping the system a few times and confirming there was no communication past GV7, we started venting the manifold section. We noted that the Kobelco's duty cycle seemed to increase audibly as the pressure in-vacuum rose, which isn't surprising given that we have 7 doors and 2x 12" ports open on the corner volume, so we elected to keep the vent slow, maybe 5 torr/minute. We stopped the vent for the night at around 400 torr. Tomorrow, we'll finish venting and open GV2.
(Travis S., Gerardo M.)
We restarted the vent on Tuesday morning, and after 45 minutes the XBM was fully vented. We opened GV2 after the XBM was fully vented, the annulus system was vented to be able to open the gate valve. No issues were encountered during the vent process or the opening of GV2.
J. Kissel, S. Koehlenbeck [remote], J. Wright, M. Simmonds Here, we post an aLOG to cover the whole week's slog, picking up where we we left off at that end of last week (LHO:90332). %%%%%%%%%%%%% Executive Summary: the remaining outstanding issue to solve before instal for the SPI pathfinder is the irregular and intermittent drift in heterodyne efficiency in the SPI's MEAS IFO (item (3) from the list of issues after finishing re-assembly up to D2400107-v5 after ECR E2600106). Importantly, we've seen this issue in the MEAS IFO even with the previous version of the assembly back in Mar 2026. After a week of hard work, we've ruled out just about everything that it could be *except* for flaws in the alignment system of the picomotor-actuated IXM100 mirror mounts which steer the MEAS beam to the MEAS IFO (see D2400107 for the annotated layout). %%%%%%%%%%%%% I spend the rest of the aLOG summarizing what we've ruled out and how. Remember -- thru out all of these studies, the REF IFO remains a rock-solid high efficiency, and the power monitor PDs so the input power on the MEAS and REF is quite stable. And a reminder for those not-so-versed in heterodyne interferometers, the primary metric is the efficiency, defined as eta = [peak-to-peak beat note amplitude] / (2 * beat note mean) (nominally 100% if the mode overlap between two interfered beams is perfect). "Drift" of this efficiency means that -- without Electronics Issues with the IFO MEAS PDs. - Suspected cause: "maybe the bias voltage is drifting?" "Something's going on with the electronic ground because we're only looking at the positive leg?" - RULED OUT: we swapped the REF B PD (which had been measuring a rock-solid, high efficiency from the REF IFO) into the MEAS B PD position, and had it measure the MEAS IFO beam. The drift was measured by the REF B PD as well. This convinces us that "it's on the incoming interfered beam. - PLUS: The bias voltage is supplied by a single circuit for all PDs in the ISIK transceiver system, so the bias-related issues would be common to REF or MEAS PDs. Spurious drive on the the picomotors - Suspected cause: "maybe the ambient electric field in the room is driving the floating pins of the picomotors, pushing the mirrors around?" - RULED OUT: At the start of the week, the picomotor signal chain was hooked up as designed from motor might-mouse to quadrupus to mock feedthru and out a ~6 ft D25 in-air cable that had been used for testing. (a) Just like we'd already done with the PDs, we hooked up ever single picomotor pin to rack power supply ground via a breakout board and clip leads at the end of the in-air cable. Still see drifts. (b) We also tried simply disconnecting all picomotors at their might-mouse connector. Still see drifts. Clipping along the MEAS path into the MEAS IFO - Suspected cause: "If there's some sort of clipping anywhere, you lose efficiency. If it's just barely clipping, the clipper might be moving / breathing with the environment." - RULED OUT: (a)Checked centering on M_M1, M_B4, M_M2, M_B3, and the two MEAS IFO PDs, and can confirm they're either :: On Optics -- offset in yaw by design (but still several beam diameters away from the optic barrel in REFL or TRANS), or :: Well-centered. (b) We'd started the week with the M_M4 and M_M5 mirror mounts and adapters in place (with no dump in either). The beam comfortably goes through the transmission ports of both adapters. But, over the course of the week, as we ruled out "everything else" out, we removed them so now they're off the board. We still see drift. (c) Confirmed that "tight-squeezes" between beam dumps still allow for at least ~1x beam diameter of clearance (on an IR card). Optics' Quality, dust and schmutz - Suspected cause: "If there's a scratch or schmutz on the optic, then maybe as the beam alignment drifts, the optical quality of the reflected beam is intermittently spoiled." - RULED OUT: We replaced all optics in the MEAS path with just-as-good, same production/coating run, equally class-A cleaned, high quality mirrors. Still see drifts. Beam quality and Optical Mode-shape - Suspected cause: "We haven't found anything, so let's look at the beam shape on a profiler. This should be the definitive answer." - RULED OUT: We removed IFO_MEAS_B, and projected the beam on to a WinCam beam profiler head, and read it's data out in the WinCam software. We looked at the beam both with a very slow heterodyne beat-note of 250 mHz, and the nominal 4096 Hz (adjusting the modulation frequency at our commercial RF source's digital interface). (a) With the MEAS IFO's alignment just tuned up, Compared mode shape and alignment during episodes of high and low efficiency, and we see nothing but excellent beam shape. (In the slow-beat-note-configuration) the only difference in profile results is the expected lower intensity when the efficiency was low. (b) We deliberately misaligned the REF and MEAS beams going into the MEAS IFO such that both beams still visible on the WinCam profile, but not interfering. No movement of beams, no mode shape change, no beam diameter change, nothing that would cause the efficiency drift. Polarization - Suspected cause: "The last thing that it could be if it's not mode shape / quality / alignment is polarization drift..." - RULED OUT: With the same IFO_MEAS_B beam, we inserted a polarizing beam splitter and monitored the s-pol power in the reflected port. S-pol (max) power (at peaks of beat note) is stable at ~10-15 [microWatt] during periods high and low efficiency. The designed p-pol light at IFO is at the 5-10 [milliWatt] level, so the extinction ratio is awesome. And we still see drifts. This also rules out, e.g. the nightmare scenario that the optics' mount PEEK set screw -- only on the MEAS path optics -- are cranked on the optic so hard that is causes birefringence. - PLUS: if there was a board-level polarization drift, the REF IFO would also be seeing this same drift. Optical Power fluctuations (Sanity Check) - Suspected cause: "I know you don't see any drift in the REF IFO, but ... is the input power drifting?" - RULED OUT: (a) The REF IFO beam samples the same beams as the MEAS IFO, and (b) Yes, we've had the power monitor PDs up on the o-cope for days, and we see no obvious or reproducible correlation. RF Modulation Modulation power fluctuations (Sanity Check) - Suspected cause: "I know you don't see any drift in the REF IFO, but ... did you check the RF electronics?" - RULED OUT: Yup, we've had the RF power monitor outputs of the laser prep chassis on the scope most of the time, and these are rock-solid and at the expected level. Environment (Insanity Check) - Suspected Cause: "The only thing that intermittently drifts on the minutes time-scales you're seeing is things like air currents and thermal effects." - RULED OUT: We tried SO MANY different combinations of (a) Clean room Lights ON/OFF (b) Room Lights ON/OFF (c) Clean room Fans ON/OFF (d) People in/out of clean room (e) People in different positions in the clean room and none of these showed obvious or reproducible correlation. Conclusion -- It's gotta be the mechanical assembly of the picomotors in the IXM100 mounts. The picomotor-actuated assembly process was documented in LHO:87497 following the assembly procedure E2500163. [1] The most accurate mechanical drawing we have the IXM mount itself D1100362 [2] The vendor drawings of the picomotor E1000197 [3] The most accurate assembly of a pico-actuated IXM mounts D1500494 and D2100433 [4] The SPI's drawings for its IXM mounts D2400144 and D2400145 Looking at the assemblies: - We're worried that the pico-motor "stopper nut" is pushing the movable-mounting plate (item 1 in [1]), rather than the pico-motor's ball bearing. And somehow this poor kinematic connection is drifting and slipping with the environment or something. - The v-groove of the item 7 in [1] carbide plate faces toward the pitch actuator, and away from the yaw actuator. While this is the right thing to do to prevent over constraint -- because the same part is used in both actuator interfaces, the ball of the pitch actuator (be it manual- or pico- driven) will sit "deeper" in longitudinal than the yaw actuator. The yaw actuators' stopper nuts all easily clear the movable mounting plate, but the pitch actuators do not. - The manually driven IXM100s show there's no issue, given that the cupped 8-100 alignment screw clears the carbide plate holes in the moveable optic-mounting plate. ACTIONS FOR NEXT WEEK We're at our wits end, and considering just ax'ing the picomotor actuation on M_B4 and M_M2. In fact, we've already replaced the mount of M_M2 with a manually driven IXM100, and may do so for M_B4 if we find enough clean IXM100 mounts. However, we've got some ideas to fix the problem and still have remote actuation: - Place a washer between the carbide plate and the front plate. - Remove the stopper nut. - Mill away parts of the front plate. - Get a thicker carbide plate. - Use only one pico-motor per holder. Pictures and further commentary to come in due time.
If it's the stopper nut on the pico-motor, which seems pretty likely, then why not just screw it in further (away from the screw tip), rather than removing it? Seems much easier than removing it, or any of the other solutions suggested above, and in fact the 'using NF picomotor products' sheet says one shouldn't remove the stopper nut. Of course, if you don't actually need the remote actuation, better to just remove the pico's and replace with manual actuators.
Fixed! see alog 90455
several things fixed, esp NPRO
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.
For clarity, this is a D1700265-V4 Ham ISI Table Baffle "Below Table"
No SN's for each of the 3 asseblies were tracked during initial install. Comments and the new SPI type 3 baffle panel as well as the type 2 that was removed will be added to D0901083 WHAM2 top level. Originally, pre SPI, the configuration would have been 2x type 01 and 1x type 02. The type 02 changes to a type 03 for the SPI configuration.
Work Permit 13238:
Change out +X-side, center, HAM2 ISI table baffle from D1700265-v4 Type 2 to D1700265-v4 Type 3 in support of SPI HAM2 ISIJ assembly install (WP:13237) per DCN E2600005 that converts HAM2-H1, XYZ Local for HAM ISI BAFFLE ASSY D1700335-v1 to -v2.
Serial numbers for these baffle assemblies can be found in LHO:90501.
