Hi Steve -
I found the doc I was looking for:
Specifically, you might find guidance in Section 5 and the pictures at the end of the doc. This should work for Vacseal as well.
Good luck - it will take some time (hours to day or 2)...
I'll be interested to know how it goes.
GariLynn helped us develop this procedure so you could also ask her to cast an eye over the setup if you are worried.
ps: there is no existing fixture to hold SOS optic while soaking it
In the attached photo from 2012, one can see the installed black glass baffle. According to the drawings (LIGO-DNNNXXX) this one has a clear aperture of 40 mm.
In (someplace ?) we have clean baffles with a 50 mm aperture which can be installed during this vent. In order to be more conservative, let us choose to swap these out for all 4 test masses during the upcoming vent using the green laser as an alignment guide, as Koji described at today's lunch meeting.
They are located at the top of E1 drawer cabinet
I've gone through the SOS suspension document (E970037) and some old elogs to get an idea of all the accesories we need for the process of suspending, aside from the tower itself, which Steve has already put together. Gautam and I have laid our eyes upon most of the critical pieces. Some other objects are unknown, and perhaps not strictly neccesary.
Confirmed to exist:
In addition, I am told that we have a long ribbon cable that can run from the X end to the clean room to enable OSEM damping control while we do the pitch alignment.
Things mentioned in the procedure I have not found:
Some other tasks and their status:
Proposed Acetone soak dish for SOS epoxy softening.
It has good acces through 5" top ID. The set up is stable and teflon lined.
Materials: glass jar with SS cover, teflon bricks, 0.008" teflon wrapped "high density Drever bricks" and aluminum
Drever brick: I beleive it is a Tungsten alloy. We used it as vac-bat savor at the coffe can. It has high density, heavy and hard, it was never identified.
I will soak one brick to see if it has any reaction ability with acetone.
NO means that only Glass and Teflon can be used for this fixture in Acetone. We can not take a chance on the coating!
I guess the small surface area Aluminum dumbbell, guide rod and-or wire standoff, magnet and epoxy does not degrade the acetone such way that it effects our coating.
Not ot mention, that only the very edge of the coating would in this solution.
Glass soaking dish with teflon guides.
Atm 1, It's right arm is perfect.
Atm 3-4, The left one has bended (dropped) end.
Atm 2, Our ruby wire stanoffs will fit the jig. Ruby OD 1.27 mm vs. old Aluminum OD 1.0 mm. Length ruby 6.4 mm vs Al 4.8 mm
Atm 5, The fixture translation stages are a bit loooose. Careful use of the micrometer is needed to be precise
Betsy agreed that the 40m will keep SOS fixtures.
Cheater cable to be used in clean room pitch gluing alingment.
Satelite amp needs to be there.
Atm 2-3, The ETMs suspension damping cable are connected at the end racks. All others go to 1X5
Atm 4-5, The other end of this cable in the high cable tray at 1X3 as shown. We'll disconnect the shorty and move the end to ETMX ( or any sus at 1X5 )
The new ETMX ruby guide rods are slightly thicker than the old aluminum ones; specifically 1.27mm vs 1.0mm.
Since we did not change the guide rod location in response to this fact, the vertical position of the suspension point changes, which in turn changes the dynamics of the suspension. Specifically, since the standoff is placed below the guide rod, the suspension point is lowered, which makes the pitch mode softer. I crunched a few numbers and have determined that this effect should not be a problem.
Given the wiki's value of the ETMX pitch resonance frequency of 0.829 Hz, I predict a the new pitch resonance frequency of 0.800 Hz.
(wiki link: https://wiki-40m.ligo.caltech.edu/Suspensions/Mechanical_Resonances)
A useful document about the dynamics of our suspension can be found at T000134
From this document, one will find that the effect of changing the suspension point height over the optic center of mass,`b`, on the pitch resonance frequency (while keeping all other dimensions equal) to be:
The top of the standoff is fixed by the guide rod, so let's say that b' is given by the position of the center of the Ruby standoff. This is then smaller than the previous b by the differences in the radii of the standoffs:
The nominal value of b is 0.985mm. Thus, the pitch resonance frequency is changed by factor of 0.965, i.e. 3.5% smaller. Then, taking the wiki value of 0.829 Hz results in 0.800Hz, a 30mHz decrease.
ITMY side : Magnet od 1.9 mm so wire to magnet gap ~ 0.2-0.3 mm
2005 ALL oplev servos use Coherent DIODE LASERS # 31-0425-000, 670 nm, 1 mW
Sep. 28, 2006 optical lever noise budget with DC readout in 40m, LIGO- T060234-00-R, Reinecke & Rana
May 22, 2007 BS, SRM & PRM He Ne 1103P takes over from diode
May 29, 2007 low RIN He Ne JDSU 1103P selected, 5 purchased sn: T8078254, T8078256, T8078257, T8078258 & T8077178 in Sep. 2007
Nov 30, 2007 Uniphase 1103P divergence measured
Nov. 30, 2007 ETMX old Uniphase 1103P from 2002 dies: .............., running time not known......~3-5 years?
May 19, 2008 ETMY old Uniphase 1103P from 1999 dies;.....................running time not known.....~ ?
Oct. 2, 2008 ITMX & ITMY are still diodes, meaning others are converted to 1103P earlier
JDSU 1103P were replaced as follows:
May 11, 2011 ETMX replaced, life time 1,258 days or 3.4 years
May 13, 2014 ETMX , LT 1,098 days or 3 y
May 22, 2012 ETMY, LT 1,464 days or 4 y
Oct. 5, 2011 BS & PRM, LT 4 years, laser in place at 1,037 days or 2.8 y
Sep. 13, 2011 ITMY old 1103P & SRM diode laser replaced by 1125P ..........old He life time is not known, 1125P in place 1,059 days or 2.9 y
June 26, 2013 ITMX 622 days or 1.7 y note: we changed because of beam quality.........................laser in place 420 days or 1.2 y
Sep. 27, 2013 purchased 3 JDSU 1103P lasers, sn: P893516, P893518, P893519 ......2 spares ( also 2 spares of 1125P of 5 mW & larger body )
May 13, 2014 ETMX, .............laser in place 90 d
May 22, 2012 ETMY,
Oct. 7, 2013 ETMY, LT 503 d or 1.4 y............bad beam quality ?
Aug. 8, 2014 ETMY, .............laser in place 425 days or 1.2 y
Sept. 5, 2014 new 1103P, sn P893516 installed at SP table for aLIGO oplev use qualification
May 23, 2016 ITMX dead laser sn P845648 replaced after 1062 days [2.9 yrs] by 1103P, sn P859884, with output output 2.6 mW, nicely round beam quality at 15 meters.
July 27, 2016 2 new 1103P from Edmonds in: P947034 & P947039, manf. date April 2016,
While tightening the bolts on the ETMX wire clamp, the wire broke. All four face magnets broke off.
Fortunately, no pieces were lost.
For the rest of this vent, at least, we need to start using the EQ stops more frequently. Whenever the suspension is being worked on clamp the optic. When you need it to be free back off the stops, but only by a few hundred microns - never more than a millimeter.
Best to take our time and use the stops often. With all the magnets being broken off, its not clear now how many partially cracked glue joints we have on dumbells which didn't completely fall off.
The clamp is in the machine for milling off the grooves. It's condition is normal. The edges needs some 800 sand paper so it is not sharp anywhere.
How did those nicks get on the edge? Fortunatelly they did not aligned with the wire.
The question arose whether we can get good enough data to diagonize our OSEM sensing matrices in air.
I just took a look at the BS spectra over the last six hours (~10PM-4AM), and the SNR looks good. The BS diagonalization itself doesn't seem so great; the POS is hugely coupled into pitch and yaw, and the angular motions are themselves coupled to each other at around 10%.
NB: use a flat-top window when you really care about peak heights that don't fall exactly on an FFT bin.
I would've liked to check this for the PRM and SRM too, but one of the PRM sensors continues to be dark, and I just noticed that all of the SRM OSEM signals are dark. ughhhh
Unbaked steel music wire from "Ca Fine Wire Co" from 24" od spool, od 0.0017" used. Identical to the one that broke.
The set up as shown with silver plated screws-washers on clamp. The unused clamp edges were sanded on P800 paper at 45 degrees just not to be very sharp.
Use your finger to feel the sharpness of edge and sand till it gets a little bit not so sharp. The drawing note is "sharp edges" on wire clamp for low loss, high Q in mind.
The wire broke at the midle with single load 295 grms
The wire hold on overnight at single load 242 grms Vezo torque wrench is not accurate! This test was performed ~ 1.5Nm DO NOT USE THIS NUMBER! (added at 8-10-2016)
This gives us a factor of 2 safety with loop suspended of 250 grms small optic.
Summary: Third unsuccessful attempt at getting ETMX suspended. I think we should dial the torque wrench back down to 1.0 N m from 1.5 N m for tightening the primary clamp at the top of the SOS tower. No damage to magnets, standoff successfully retrieved (it is sitting in the steel bowl)
Unfortunately I don't know of a more deterministic way of deciding on a "safe" torque with which to tighten the bolts except by trial and error. It is also possible that the clamping piece is damaged in some way and is responsible for these breakages, but short of getting the edges chamfered, I am not sure what will help in this regard.
Unrelated to this work: earlier today before the first wire failure, while I was optimistic about doing fine pitch balancing and gluing the standoff, I set up an optical lever arm ~3m in length, with the beam from the HeNe on the clean bench at 5.5 in above the table, and parallel to it (verified using Iris close to the HeNe and at the end of the lever arm). I also set up the PZT buzzer - it needs a function generator as well for our application, so I brought one into the cleanroom from the lab, isopropanol wiped it. The procedure says apply 5Vrms triangular wave at 1000Hz, but our SR function generators can't put out such a large signal, the most they could manage was ~2Vrms (we have to be careful about applying an offset as well so as to not send any negative voltages to the PZT voltage unit's "External input". All the pieces we need for the fine pitch balancing should be in the cleanroom now.
Gautam and Steve,
The clamp's left side was jammed onto the left guide pin. It was installed slit facing left. Gautam had to use force to remove it. The clamp should move freely seating on the guide rods till torque aplied. Do not move on with the hanging of optic with a jammed clamp. Fix it.
Never use force as you are hanging - aligning optic. The clamp is in the shop for resurfacing and slit opening.
[lydia, steve, ericq, gautam]
Here are the photos we took showing the magnet positions in the OSEMs, and others showing the positions of the wire and unglued standoff. These were taken before the pitch balancing adjustment Gautam described, which apparently cause UR to be a little too high. Thoe OSEMs were all inserted only until the ends of the magnets were almost inside, to lower the risk of knocking any magnets off.
At the time of these pictures, all magnets except LL were intentionally positioned slightly above the center of the OSEM in anticipation of wire sag. The LL magnet was approximately centered in the OSEM. It was not possible to get both LL and UL the same height relative to their respective OSEMs, possibly due to a spacing error when they were glued to the optic.
Attachment 1: Position of wire along bottom of the optic. Looks adequately centered and not kinked.
Attachment 2: Photo showing good contact between the sandoff and the barrel of the optic. The standoff does not appear to be resting on glue from the guiderod.
Attachment 3: Shows position of standoff and wire after rough pitch banacing. Wire is visibly resting in the groove.
Attachment 4: SD magnet location photographed through OSEM.
Attachment 5: LL magnet location photographed through OSEM.
Attachment 6: LR magnet location photographed through OSEM.
Attachment 7: UL magnet location photographed through OSEM.
Attachment 8: UR magnet location photographed through OSEM.
Ni plated SmCo magnets with specification of LIGO-C1103521-v2 for SOS ordered from Electron Energy Corp
100 pieces of Ni- Platted magnets are in 9-27-2016 They are stored at clean cabinet S15
EP30-2 epoxy 1/2 pt kit 250 ml of part A and 25 ml of part B should be here in 7 days. These can packed epoxy is much more economical than the double barrel cartridges.
Spare SOS wire clamps will be out of the machine shop next week.
[lydia, ericq, gautam]
Lydia also briefly played around with the IR camera to inspect the OSEMs. A more thorough investigation will be done once the cage is in for air baking. From our initial survey, we feel that the beams are pretty well aligned along the straight line between PD and LED - we estimate the upper bound on any misalignment to be ~10 degrees.
Part 1: Rotation of optic
Part 2: Replacement of holder for top pair of OSEMs
Part 3: Fine pitch balancing
Attachment #1: Striptool trace showing OSEMs are pretty well centered (towards the end, I turned on the HEPA filters again, which explains the shift of the traces). The y-axis is normalized such that the maximum displayed corresponds to the fully open PD output of the coils
Attachment #2: Fine pitch balancing optical lever setup
Attachment #3: Tower assembly
Attachment #4: SIDE OSEM close-up
Attachment #5: UR OSEM close-up
Attachment #6: UL OSEM close-up
Attachment #7: LL OSEM close-up (this is the concerning one)
Attachment #8: LR OSEM close-up
We should also check the following (I forgot and don't want to wear my clean jumpsuit again now to take more photos):
If only the LL magnet looks too low, doesn't this mean that the OSEMs are not arranged in a square shape?
If so, you can fix this misalignment by moving the OSEM holding plate rather than OSEM shimming, can't you?
0.0017" OD., 500ft steel music wire ordered. Pictures of the existing roll are below. It will be on 8" OD. spool too.
Attachment #1: Wire is in the groove in the unglued wire-standoff, groove rotation looks pretty good.
Attachment #2: Ruby standoff is sitting on the barrel of the optic (if you zoom in)
Attachment #3: Side magnet is well centered w.r.t OSEM coil
Attachment #4: UR magnet is well centered w.r.t OSEM coil
Attachment #5: UL magnet is well centered w.r.t OSEM coil
Attachment #6: LL magnet is well centered w.r.t OSEM coil
Attachment #7: LR magnet is well centered w.r.t OSEM coil
Attachment #8: Wire is in the groove in the glued Ruby standoff
Attachment #9: Standoff after gluing. 3-4 drops of epoxy are visible on the wire, but none looks to have seeped into the groove itself
Attachment #10: Side view of newly glued Ruby standoff
Attachment #11: Before and After gluing shots.
I came in to check on ETMX. I freed the earthquake stops, and found that the OSEMS were reasonably, but not perfectly, centered. Turning on the damping, I found that the pitch balance is biased slightly downwards at about ~0.5mrad, which is acceptable.
As another check for how much we moved the standoff while gluing, we can look at the spectra of the OSEMS while the mirror is free swinging, and see if/how the resonance frequencies have moved around. As Gautam previously mentioned, the pitch frequency is even softer than we expected from the thicker ruby standoff alone. This is due to the excess glue around the guide rod forcing us to position the standoff even lower to have good contact with the optic's barrel. In the plot below, the design yaw/pit/pos frequencies are the dashed lines, and the measured frequencies are the solid lines.
[The plot is not in spectral density units, so that the peak heights reflect real units of motion at each resonance frequency. Data and code used to generate the plot is attached]
According to the calculations from ELOG 12316, this pitch frequency implies the support point is 0.317mm lower than the design value of 0.985mm. (However, this is just an approximation and does not include the fact that each standoff is at a different height.)
Nevertheless, this difference is frequency is not so large that the dynamics of the suspension will be qualitatively changed in some important way; really, the pitch frequency is just ~1.5dB lower. So, I deemed our standoff gluing a success, removed the optic from the suspension, and placed it in an optic holding ring after giving the top of the barrel a gentle drap wipe with some iso. At this point, I used the microscope to look at the ruby standoff groove. As far as I can tell, no glue has invaded the groove - it looks sharp as ever. (whew)
I also wiped the wire with acetone and easily removed the glue droplets. However, I noted that (as is the case for ETMY) the wire is deformed at the points where it was in contact with the standoffs. I wonder if we should re-suspend with new wire, or accept the current deformed wires.
In any case, we can now move on to air baking the ETMX tower and gluing the stray magnet back onto ETMY.
Given that ETMX looks to be in good shape and the optic and suspension tower are ready for vacuum and air bakes respectively, I set about re-gluing the knocked off magnet of ETMY. In my previous elog, I had identified the knocked off magnet as the UL magnet. But in fact, it was the LR magnet that broke off. This is actually one of the magnets that was knocked off when Johannes was removing the optic from the vacuum chamber. I have edited the old elog accordingly.
Step 1: Removing epoxy residue
Step 2: Putting the optic in the magnet gluing jig
Step 3: Gluing the magnets
Provided the gluing goes well, the plan for tomorrow is:
The pickle pickers came off nicely and both magnets seem to be glued on okay. The alignment of the face magnets look pretty good, but we will only really know once we suspend the mirror, check the pitch balance, and put in the OSEM coils.
I brought the ETMY suspension tower + OSEM coils out of the vacuum chamber into the cleanroom. Given that the old wire had a pretty sharp kink in it, I removed it with the intention of suspending the optic with a new length of wire. I noticed a few potential problems:
Attachment #1 - ETMY tower is different from ETMX tower:
Attachment #2 - the base of the tower is significantly rusty:
I am holding off on attempting to re-suspend the optic for now, until we decide if the old wire grooves need to be removed or not. If we are okay with re-using the same piece as is, or if we are okay with using sandpaper and not the machine shop to remove the grooves, I will resume the re-suspension process.
Eric suggested another alternative, which is to use the old ETMX tower. I don't recall it being rusted, but this has to be checked again. The other problem of the wire-grooves would possibly still be an issue.
Regarding the vacuum bake of the ETMs, Bob tells us that the best case scenario we are looking at is September.
New Wiha 28504 torque wrench for SOS wire clamping. It's range 7.5 - 20 in-lb in 0.5 steps [ 0.9 - 2.2 Nm ] Audible and perceptible click when the pre-set torque has been attained at ±6% accuracy.
The new ETMX sus wire torqued to ~ 11.5 in-lb [1.3 Nm ]
Rana felt it was alright to use the wire clamp and suspension cage in its existing condition for checking the ETMY magnet-OSEM coil alignment. So we set about trying to re-suspend ETMY. The summary of our attempts:
Regarding the vacuum bake of the optics: why do we want to do this again? Koji mentioned that the EP30-2 curing process does not require a bake, and there is also no mention of requiring a vacuum bake in the EP30-2 gluing guide. Is there any other reason for us to vacuum bake the optic?
The 7.5 in-lb of Wiha seems at the upper end of torque range for a 4-40 SS screw
Wiha 28502 ordered with range 5 -10 in-lb for silver plated 4-40 screws
Do not trust the Venzo torque wrench under 2 Nm ! It miss lead me.
Recommended torque values for silver-plated fasteners are here. For aLIGO we use the guidelines in T1100066-v6, This doc is posted in 40m wiki under Mechanics also.
So, we'll use 6 in-lbs on silver plated 18-8 stainless steel socket head cap screw 4-40 x 3/8 into SS tower bridge.
Please replace these clamp screws every time if they were tightened without a torque wrench.
Attachment #1: Striptool trace showing all OSEM coils have been pushed in till the PD readout is approximately half the fully open value
Attachment #2: Pitch balance is off by ~2.8mrad (the Iris center is 5.5" above the table)
Attachment #3: UR magnet
Attachment #4: UL magnet
Attachment #5: LR magnet
Attachment #6: LR magnet
Attachment #7: SD magnet
How much pitch bias do you need in order to correct this pitch misalignment?
That may give you the idea how bad this misalignment is.
How much pitch bias do you need in order to correct this pitch misalignment?
That may give you the idea how bad this misalignment is.
I needed to move the pitch slider on the IFO align screen to -2.10 (V?) from 0 to get the HeNe spot to the center of the iris. The slider runs from -10V to 10V, so this is something like 10% of its range. I am not sure if it means anything, but the last saved backup value of this pitch slider was -3.70. Of course, application of the bias will affect all the coils, and when the optic is pitch balanced, the lower magnets are a little too far out and the upper magnets are a little too far in (see Attachment #1), as we expect for a downward pitch misalignment to be corrected. I suppose we can iteratively play with the coil positions and the bias such that the coils are centered and we are well balanced (maybe this explains the old value of -3.70).
I also checked that the side magnet can completely occlude its PD. With the damping on, by pushing the coil all the way in, the output of the side PD went down to 0.
The wire will arrive in 1-2 weeks. It is a new production. Brad Snook of Ca Fine Wire was suprised that we are still using the 13 years old wire. Oxidation is an issue with iron contained steel wire.
He would not give me a shelf life time on it. He recommended to check the strenght of it before usage. It passed with safety factor of 2 just recently.
In the future we'll store the new spool in oxigen free nitrogen environment..
0.0017" OD., 500ft steel music wire ordered. Pictures of the existing roll are below. It will on 9" OD. spool too.
We have indeed seen numerous tarnished/rusty points along the wires, and just tried to choose lengths free of any of these. I wonder if this can explain the brittleness/ease with which we've been breaking it. My feeling is that we should use the newer wire if feasible.
I assume that we are prepared to live with the pitch bias situation of ETMY (i.e. we can achieve a configuration in which there is some pitch bias to the coils, and the OSEMs are inserted such that the PD outputs are half their maximum value). Or at least that we don't want to go through the whole standoff-regluing procedure for ETMY as well.
So today I took the optic out, and began to make some preparations for the air bake.
In summary, the questions that remain (to me) are:
I think we can start the baking of the optics tomorrow. The timeline for the suspension towers is unclear, depends on how we want to deal with the sanding dilemma.
The SOS ETMY tower had and Aluminum bridge. How is it possible that this was true? Is SS better than Al for some quantitative scientifc reason ???
Their weight ratio as measured = 922 / 307 g = 3
Destinies: SS 304 / Al 6061 > 0.289 / 0.098 [ lb /in3 ] = 2.94
I put in both ETMX and ETMY into the air-bake oven at approximately 8.45pm tonight. They can be removed at 8.45am tomorrow morning.
I turned off the air bake oven at 8:45AM. I'll leave the optics alone for a bit while it cools.
Not really true that it passed. That's just an arbitrary margin. Best to throw away all the old wire. We have no quantitative estimate of what the real torque should be. Its just feelings.
I just put in the following into the air bake oven for a 12 hour, 70C bake:
I put these in at 10.30pm. So the oven will be turned off at 10.30am tomorrow morning. The oven temperature seems stable in the region 70-80 C (there is no temperature control except for the in built oven control, I just adjusted the dial till I found the oven remains at ~70C.
Tomorrow, we will look to put on first contact onto the ETMs, and then get about to re-suspending them.
The wire inprints were removed by 800P grain paper [Norton 73568] The SS bridge block now has an undesireble vally in the wire location.
The sus bridges were soaked in acetone over night and sonicated to remove residual sand paper.
I took the two cages, wires and wire clamps out this morning, back into the cleanroom after their 12 hour 70C bake.
I've also applied first contact to the AR face of the optics. Steve is preparing a jig which will allow us to apply first contact on the HR side with the optic horizontal. The idea is to apply a large coating first, to clean the bulk of the HR surface, and peel it off before re-suspending the optic. Then we can paint on a smaller area, suspend the optic (and hope the pitch balancing is alright) before taking the whole assembly into the chamber where it will be peeled off.
Calum recommended that we buy a new ionizing gun + electrometer assembly (apparently our current set up is woefully obsolete) but I don't know if we can have these in time for the first contact peeling...
Stress Relieved 0.0017" Music Wire CFW P/N: CFW2035025, Made 08-17-2016
GBL (grams breaking load )
UTS (ultimate tensile strength)
YTS (yield tensile strength)
I've applied first contact to both the ETMs. They're now ready to be suspended. I've also cut up some lengths of the new wire and put them in the oven for a 12 hour 70C bake.
Unless we want the AR surface to also have a small F.C coat until the optic is in the vacuum chamber, I think I will proceed with re-suspending the ETMs..
Today morning, I suspended ETMY and made the same checks dscribed below. The clamping went smoothly, 5 in. lb. of torque seems sufficient, in the limited observation time, there has been no evidence of wire sag. Today afternoon, we will go about putting the OSEM coils in, setting their equilibrium points etc. This may need to be re-done once the optic is in the chamber and the first contact has come off, but at least we can coarsely place them in the relative convenience of the cleanroom.
GV EDIT 9.15pm 22 Aug: Eric had a look at both towers and pointed out that I had neglected to use washers on the wire stops. After consultation with Steve, I decided that it is not worth it to remove the clamp and re-suspend the optic - it is likely that the current suspension process will have caused new grooves in the suspension block, which will have to be removed, and the sanding process did not work so well last time. In any case, the net effect of this will be that the actual torque with which the clamp is tightened will be slightly different from 5 in. lb., but since there is no evidence that the clamp isn't tight enough / is too tight, I think it is okay to push ahead.
We worked on trying to insert the OSEMs in the optimal positions such that the coupling of the bounce mode into the OSEM sensor signals was minimised.
First, I gave the barrel of the optic a wipe with some optical tissue + acetone in order to remove what looked like some thin fibres of dried first contact. It may be that while I was applying the F.C., the HEPA air flow deposited these on the barrel. In any case, they came off easily enough. There is still a few specks of dust on various parts of the barrel, but it is likely that these can just be removed with the ionized air jet, which we can do after putting the optic in the chamber.
We then did the usual OSEM insertion till the magnets neutral position was such that the sensor output was ~50% of the fully open value (turned the HEPA off for the remainder of this work). I tweaked the bottom OSEM plate a little in order to center the magnets relative to the coil as best as possible. Once this was done, we attempted to look at spectra of the sensor outputs, with 0.05 Hz bandwidth - however, we were unable to identify any peak at 16.4 Hz, which is what a Jan 2015 measured value wiki page claims the bounce mode frequency is (although this was an in vacuum measurement). There were a couple of peaks at ~15.7 Hz and ~16.7 Hz, but I can't think of any reason why the bounce mode resonance should have changed so much - after all, this is ETMY for which no standoff regluing was done. The only difference is that there is some first contact + peek mesh on the HR face now, but I doubt this can modify the bounce resonance frequency so much (this is just my guess, I will have to back this up with a calculation).
Anyways we decided to take this up again tomorrow. Things are progressing fairly well now, I hope to be able to put in ETMY back into the chamber at some point tomorrow and commence re-alignment of the interferometer. I've left the OSEMs in for today, with the EQ stops not engaged but close by. HEPA has been turned back on.