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ID Date Author Type Category Subject
12101   Fri Apr 29 16:13:36 2016 ericqUpdateLSCGreen PDH demod lowpass

We can get as much, if not more, attenuation of the 1F line in the mixer output that we get from the post-mixer LPF from using the following passive filter between the PD and mixer RF input:

There should still be some kind of LPF after the mixer, but I haven't yet determined what it should be; this will determine how much phase the PDH loop wins. At most, this should win around 25 degrees at 10kHz.

The filter was designed by referencing the "Handbook of Filter Synthesis" by Zverev, looking for an elliptic filter for matched source and load impedences, 40dB min attenuation in the stopband, a stopband frequency that starts at twice the corner frequency, and minimizing the VSWR between the PD and filter in the passband.

In terms of the tables in the book, this means: n=5, rho=2%, theta=30deg, K**2 = 1.0. The dimensionless component values were scaled by the corner frequency of 200kHz, and reference impedence of 50 Ohm. (The corner is a little lower than the real modulation frequency, since the nonzero resistance of the inductors pushes the frequency up a bit)

The ideal capactior values do not correspond to things we have in hand, so I checked our stock and chose the closest value to each one.Unsurprisingly, due to these component substitutions, and the fact that the coilcraft inductors have a resistance of about 7 Ohms, the predicted TF of the realizable filter does not match the design filter exactly. However, the predicition still looks like it will meet the requirement of 40dB of supression of the 2F line in the PD signal. (Since we have tunable inductors, I've used the ideal inductor values in generating the TF. In practice I'll inspect the TF while I tune them)

 Desired Realizable C1 8.28 nF 10 nF C2 1.39 nF 1.5 nF C3 19.6 nF 22 nF C4 4.22 nF 4.7 nF C5 6.08 nF 6.8 nF L2 43.1 nH 32-48 nH + 7 Ohm L4 34.4 nH 32-48 nH + 7 Ohm

[In this TF plot, I've multiplied the real response by 2 to account for the voltage division that occurs with ideal 50 Ohm impedance matching, to make 0dB the reference for proper matching]

The filter's phase delay at the modulation frequency is just about 180, which as a time delay of 5usec works out to 9 degrees of phase loss at 10kHz in the PDH loop. According to some old measurements, the current LPF costs something like 35 degrees at 10k, so this wins at most around 25 degrees, depedent on what LPF we put after the mixer.

LISO source both traces is attached!

Attachment 3: elp_liso.zip
12106   Thu May 5 04:05:03 2016 ericqUpdateLSCAux X PDH checks

We took an OLG measurement of the green PDH loop. It seems consistent with past measurements. I've added a trace for the the post-mixer lowpass, to show its contribution to the phase loss. (EDIT: updated with measured LPF TF)

I used this measured OLG and the datasheet laser PZT conversion factor to calibrate the control signal monitor into the AUX laser frequency noise, it looks consistent with the frequency noise measured via the PSL PLL (300 Hz/rtHz @ 100Hz). Above a few tens of kHz, the control signal measurement is all analyzer noise floor, due to the fourth order 70kHz lowpass after the mixer (the peaks change height significantly depending on the analyzer input range, so I don't think they're on the laser). Gautam will follow up with more detailed measurements of both the error and control signals as he noisebudgets, this was just intended as a quick consistency check.

12107   Thu May 5 14:03:52 2016 ericqUpdateLSCFurther Aux X PDH tweaks

This morning I poked around with the green layout a bit. I found that the iris immediately preceding the viewport was clipping the ingoing green beam too much, opening it up allowed for better coupling to the arm. I also tweaked the positions of the mode matching lenses and did some alignment, and have since been able to achieve GTRX values of around 0.5.

I also removed the 20db attenuator after the mixer, and turned the servo gain way down and was able to lock easily. I then adjusted the gain while measuring the CLG, and set it where the maximum gain peaking was 6dB, which worked out to be a UGF of around 8kHz. On the input monitor, the PDH horn-to-horn voltage going into the VGA is 2.44V, which shouldn't saturate the G=4 preamp stage of the AD8336, which seems ok.

The ALS sensitivity is now approaching the good nominal state:

There remains some things to be done, including comprehensive dumping of all beams at the end table (especially the reflections off of the viewport) and the new filters to replace the current post-mixer LPF, but things look pretty good.

Attachment 1: 2016-05-05_newals.pdf
12110   Fri May 6 16:42:12 2016 ericqUpdateLSCGreen PDH demod lowpass

I've build the filter, and it seems to have the desired TF shape.

I also re-purposed the 70k lowass to a ~120k lowpass by changing the 68nF caps to 22nF caps, since we still want some post-mixer rolloff.

However, putting the ELPF in the chain caused some weird shapes in the OLG. I still need to get to the bottom of it. However, just with the post-mixer LPF modification, here's what the OLG looks like:

As Rana surmises, we definitely still add a boost and maintain a 10k UGF. I still need to look into the state of the remote boost....

12112   Sat May 7 09:40:40 2016 ericqUpdateLSCGreen PDH demod lowpass

As I was looking at filter designs, it seemed difficult to get 40dB of supression at 2F with a bandpass without going to a pretty high order, which would mean a fair number of lossy inductors.

I'll keep working on it. Maybe we don't need 40dB...

12114   Tue May 10 03:44:59 2016 ericqUpdateLSCRelocked

ALSX noise is solidly within past acceptable performance levels. The DRFPMI was locked on four out of six attempts.

Some housekeeping was done:

• PMC aligned
• Static alignment voltages of X end PZT mirrors offloaded by turning mount screws
• Rough comissioning of AUX X dither alignment
• Locking scripts reverted to AUX X Innolight voltage/temperature sign convention

The recombination of the QPD signals to common / differential is imperfect, and limited how well we could keep the interferometer aligned, since the QPD at X has changed. This needs some daytime work.

Some sensing matrix measurements were made, to be meditated upon for how to 1F the DRMI.

Other to-dos:

• Bandpass + notch combo for green refl PDs
• SRCL, and to a lesser extant, MICH feedforward subtraction (See DARM vs. other length DOF coherence plot below)
• Fiber couple AUX X light
• Make IFO work good

As an aside, Gautam and I noticed numerous green beams coming from inside the vacuum system onto the PSL table. They exist only when green is locked to the arms. Some of them come out at very non-level angles and shine in many places. This doesn't make me feel very happy; I suppose we've been living with it for some time.

Attachment 1: 2016-05-10_DARMcoherence.pdf
12115   Wed May 11 16:39:01 2016 ericqUpdateVACc0rga alive, output wonky
 Quote: Our last RGA scan is from February 14, 2016  We had a power outage on the 15th Gautom has not succeded  reseting it. The old c0rga computer looks dead. Q may resurrect it, if he can?

The c0rga computer was off, I turned it on via front panel button. After running RGAset.py, RGAlogger.py seems to run. However, there are error messages in the output of the plotrgascan MATLAB script; evidiently there are some negative/bogus values in the output.

I'll look into it more tomorrow.

12128   Tue May 24 10:21:36 2016 ericqSummarySUSITMX Oplev loops

I did a quick measurement of the ITMX oplev loops, both pitch and yaw have about the same upper UGF as previous measurements with the previous laser; about 4 Hz.

12131   Tue May 24 23:17:37 2016 ericqUpdateCOCFinesse modelling - mode overlap scans

I think you should use the current actual PRC & SRC cavity lengths as measured, as it would be simplest to simply replace the folding mirror optics without changing the macroscopic lengths / optic positions. (EDIT: Gautam rightly points out that we have to move things around regardless, since our current lengths include propagation through the folding mirror subtrates)

Moreover, the recycling cavity lengths you posted are not the right "ideal" lengths to use, as they do not account for the complex reflectivities of the sidebands off of the arm cavities (I have made this mistake myself). See this 40m wiki page for details.

In short, given our current modulation frequency, the ideal lengths to use would be:

• Ideal arm length of 37.795 m
• Ideal PRC length of 6.753 m
• Ideal SRC length of 5.399 m

These are the lengths that the recycling cavity optics were positioned for (though we did not achieve them perfectly). If you do a finer PRC/SRC length scan around the DRFPMI resonance of your model, you would presumably see some undesired sideband splitting.

12132   Wed May 25 02:54:09 2016 ericqUpdateGeneralOdds and ends

WFS locking point seemed degraded; I hand aligned and reset the WFS offsets as usual.

ITMX oplev recentered. While doing so, I noticed an ETMX excursion rear its head for the first time in a long while :

There was no active length control on ETMX, only OSEM damping + oplevs. Afterwards, its still moving around with only local damping on. I'm leaving the oplevs off for now.

12138   Fri May 27 02:52:53 2016 ericqUpdateLSCRestoring high BW single arm control

I've been futzing with the common mode servo, trying to engage the AO path with POY for high bandwidth control of a single arm lock. I'm able to pull in the crossover and get a nice loop shape, but keep getting tripped up by the offset glitches from the CM board gain steps, so can't get much more than a 1kHz UGF.

As yutaro measured, these can be especially nasty at the major carrier transitions (i.e. something like 0111->1000). This happens at the +15->+16dB input gain step; the offset step is ~200x larger than the in-loop error signal RMS, so obviously there is no hope of keeping the loop engaged when recieving this kind of kick. Neither of the CM board inputs are immune from this, as I have empirically discovered. I can turn down the initial input gain to try and avoid this step occuring anywhere in the sequence, but then the SNR at high frequencies get terrible and I inject all kinds of crud into the mode cleaner, making the PC drive furious.

I think we're able to escape this when locking the full IFO because the voltages coming out of REFL11 are so much larger than the puny POY signals so the input-referred glitches aren't as bad. I think in the past, we used AS55 with a misaligned ITMX for this kind of single arm thing, which probably gives better SNR, but the whole point of this is to keep the X arm aligned and lock it to the Y-arm stabilized PSL.

12145   Wed Jun 1 16:28:28 2016 ericqUpdateElectronicsCommon board Op amp input offsets

I used a Eurocard extension board to peek at the inputs and outputs of each of the gain-ladder AD829s on input B of the CM board in the +31dB configuration with the input terminated. (i.e with the following stages active in this order: +16dB, +8dB, +4dB, +2dB, +1dB).

The voltages I observed imply that the +8dB stage has an input voltage offset of -2mV, whereas all the other positive gain stages show around +-0.5mV. This could explain the shift observed at the +15->+16 transition. (However, since both input channels show a jump here, maybe its something more systemic about the board...)

In any case, it should be simple enough to swap out a new AD829 in place of U9B and see if it improves things, before getting too deep into the muck. (In principle, the AD829 has offset nulling pins, but I'm not sure how to do it in a non-hacky way since the board doesn't have any pads for it.)

12147   Fri Jun 3 12:53:44 2016 ericqUpdateElectronicsCommon board Op amp input offsets

I replaced some of the AD829s with other AD829s, but the offset situation didn't improve.

However, I figured that we don't really need the ~100MHZ bandwidth of the AD829, since the IMC loop limits us to a ~10kHz CARM bandwidth. Also, since we don't routinely use IN2 for anything, I felt free to try something else.

Specifically, I replaced all of the positive gain AD829s in the input 2 gain ladder with OP27s (U8B->U12B on D1500308), which should have input offset voltages ~30x lower than the AD829s.

Here is a comparison of the outputs these configurations perform, normalized to the output at the +0dB gain setting - where all of the op amps in the gain ladder are bypassed.

So, most of the transitions now result in an output offset change of less than 0.5mV, which is nice.

The exception seems to be where the +8dB stage is switched in or out. I may try replacing this one, as these transitions cause a lock loss now when trying to lock the arm with high bandwidth using POY.

12148   Fri Jun 3 13:05:18 2016 ericqUpdateCDSCDS Notes

Some CDS related things:

Keith Thorne has told us about a potential fix for our framebuilder woes. Jamie is going to be at the 40m next week to implement this, which could interfere with normal interferometer operation - so plan accordingly.

I spent a little time doing some plumbing in the realtime models for Varun's audio processing work. Specifically, I tried to spin up a new model (C1DAF), running on the c1lsc machine. This included:

• Removing the unused TT3 and TT4 parts from the IOO block in c1ass.mdl, freeing up some DAC outputs on the LSC rack
• Adding an output row to the LSC input matrix which pipes to a shared memory IPC block. (This seemed like the simplest way for the DAFI model to have access to lots of signals with minimal overhead).
• Removing two unused ADC inputs from c1lsc.mdl (that went to things like PD_XXX), to give c1daf.mdl the required two ADC inputs - and to give us the option of feeding in some analog signals.
• Editing the rtsystab file to include c1daf in the list of models that run on c1lsc
• Editing the existing DAFI .mdl file (which just looked like an old recolored cut-n-paste of c1ioo.mdl) to accept the IPC and ADC connections, and one DAC output that would go to the fibox.

The simple DAFI model compiled and installed without complaint, but doesn't succesfully start. For some reason, the frontend never takes the CPU offline. Jamie will help with this next week. Since things aren't working, these changes have not been commited to the userapps svn.

12151   Mon Jun 6 16:41:36 2016 ericqUpdateCDSFB upgrade work

Barring objections, starting tomorrow morning, Jamie will be testing the new FB code. The IFO will not be available for other use while this is ongoing.

12168   Fri Jun 10 16:19:03 2016 ericqUpdateSUSETMX watch

ETMX has been jumping around again lately. Just now, I zeroed the ETMX alignment offsets in the SUS model, and centered the ETMX oplev spot via slow machine sliders. OSEM damping is on, oplev damping is off. Let's see how it moves around in the next day or so.

GPS: 1149635923

UTC: Jun 10 2016 23:18:26

12177   Tue Jun 14 15:55:17 2016 ericqUpdateSUSETMX watch

Within two hours, it was already all over the place.

## It has been Decided: we will assemble a suspension with the spare ETM optic with the current-generation standoff for installation ASAP. I.e. no new custom parts. We will continue pursuing the new standoff design, but we need our interferometer back.

12189   Thu Jun 16 12:06:59 2016 ericqUpdateLSCRF Amp installed at POY11 RF output

I have installed a ZFL-500LN on the RF output of POY11. This should reduce the effect of the CM board voltage offsets by increasing the size of the error signal coming into the board. Checking with an oscilloscope at the LSC rack, the single arm PDH peak to peak voltage was something like 4mV, now it is something like 80mV

The setup is similar to the REFL165 situation, but with the amplifier in proximity with the PD, instead of at the end of a long cable at the LSC rack.

The PD RF output is T'd between an 11MHz minicircuits bandpass filter and a 50 Ohm terminator (which makes sure that signals outside of the filter's passband don't get reflected back into the PD). The output of the filter is connected directly to the input of the ZFL-500LN, which is powered (temporarily) by picking off the +15V from the PD interface cable via Dsub15 breakout. (I say temporarily, as Koji is going to pick out some fancy pi-filter feedthrough which we can use to make a permanent power terminal on the PD housing.)

The max current draw of this amplifier is 60mA. Gazing at the LSC interface (D990543), I think the +15V on the DSUB cable is being passed from the eurocard crate; I don't see any 15V regulator, so maybe this is ok...

The free swinging PDH signal looked clean enough on a scope. Jamie is doing stuff with the framebuilder, so I can't look at spectra right now. However, turning the POY whitening gain down to +18dB from +45dB lets the Y arm lock on POY with all other settings nominal, which is about what we expect from the nominal +23dB gain of the amplifier.

I would see CM board offsets of ~5mV before, which was more a little more than a linewidth before this change. Now it will be 5% of that, and hopefully more manageable.

12205   Tue Jun 21 04:01:09 2016 ericqUpdateLSCY arm @ 30kHz UGF w/POY, AO

With the newly amplified POY signal, locking the mode cleaner to the Y arm at ~30kHz bandwidth was quite straightforward. The offset jumps still happen, and are visible in POY11_I_ERR, but are never big enough to cause much power degradation in TRY (except when turning on CM board boosts, but its still not enough to lose lock). The script which accomplishes this is at scripts/YARM, and is in the svn. The MC2/AO crossover is at about 150Hz with 40deg margin.

For now, I'm using IN1 of the CM board, because I haven't removed the op27s that I put into IN2's gain stages. I believe the slew rate limitations of these prevent them from working completely during the offset jumps. I'll put AD829s back soon.

At first, I had ITMX misalgined to use AS55 as an out of loop sensor, then I aligned and locked the X arm on POX to compare.

Weirdly enough, locking the mode cleaner to the Y arm with 30kHz UGF and two boosts on make no real visible difference in the X arm control signal. This is strange, as the whole point of this affair was to remove the presumably large influence of frequency noise on the X arm signals... Maybe this is injecting too much POY sensor noise?

Attachment 1: inloop_outloop.pdf
Attachment 2: xarm.pdf
12208   Tue Jun 21 11:49:29 2016 ericqFrogsCDSmedm command not working

The workstations' .bashrc is a symbolic link to /users/controls/.bashrc

In it, someone commented out the critical line:

#source /ligo/cdscfg/workstationrc.sh

I uncommented it. medm (and all of the other things like cdsutils) work again.

I blame jamie.

12213   Thu Jun 23 17:24:32 2016 ericqUpdateGeneralTweaks

I spent some time this afternoon reviving some of my CESAR/ESCOBAR shenanigans on the Y arm. I found it neccesary to adjust a few things.

• PMC realigned
• ETMY oplev centered
• Y End green realigned
• PSL/Y Green beat realigned

Afterwards, ALSY noise levels were good.

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:

• Guide rod gluing fixture
• 3 axis micrometer + microscope doohicky
• PZT buzzer (for fine standoff positioning)
• Winch fixture (the plate maybe doesn't fit perfectly on the top of the SOS tower, but one bolt will probably work)
• Spare guide rods and ruby standoffs
• Magnet+dumbell gluing fixture (in case we need to glue a new magnet+dumbell pair)
• Magnet to optic gluing fixture (including "pickle pickers"/grippers)
• 0.017" suspension wire
• HeNe laser + QPD + beam height target (confirmed working on scope)

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.

• Something called an "SOS set screw tool" (D961412)
• Not mentioned specifically what this is for
• Edmund scientific pocket measuring microscope + bushing
• Seems to be intended for centering OSEM holding plate on the magnet position. I found no mention of this use in 40m elogs. It can likely be done by eye
• SOS cleaning bracket (D970181)
• This is likely for the old liquinox cleaning procedure. We'll be using first contact.

Some other tasks and their status:

• Check cleanroom table levelling:
• Done via 12" spirit level, looks good
• Glue removal strategy / fixture
• Steve is working on this
• Cut and apply viton tips to earthquake stops
• Either gautam will do this, or we will use the current suspension's stops
12233   Thu Jun 30 16:11:57 2016 ericqUpdateGeneralVent Prep

I have updated the vent prep checklist on the wiki. Gautam and I did the following things from it:

• Center all oplevs, transmon QPDs
• ETMX oplev has not been centered, since it's moving around so much, and we're going to immediately move the suspension anyways.
• Align the arm cavities for IR and align the green lasers to the arms.
• AUX X Green was aligned while the X arm was well aligned. Soon thereafter, ETMX wandered away, but the green will remain a good reference
• Update the SUS Dritmon values
• Reconcile all SDF differences
• Reduce input power to no more than 100mW by adjusting wave plate+PBS setup on the PSL table BEFORE the PMC. (Using the WP + PBS that already exist after the laser.)

• Replace 10% BS before MC REFL PD with Y1 mirror and lock MC at low power.
• I don't think we've vented since the most recent slew of changes to the IMC servo, so its not surprising that the current low power scripts don't work. I'm working on locking the IMC, but this does not prevent us from initiating the vent tomorrow.

The following bullets have not yet been executed:

• Close shutter of PSL-IR and green shutters at the ends
• Make sure the jam nuts are protecting bellows
• Check crane functionality & cleanliness

• Turn off HV into vacuum: OMC is not wired this time
• Particle count must be under 10,000 counts / cf min for 0.5 micron
• Check all metal window covers are on.
• Check 5 cylinders (24 cft size) of instrument grade air, called Alfa Gas 1 in stock.
12235   Thu Jun 30 21:24:36 2016 ericqUpdateGeneralVent Prep

Steve has ordered some teflon parts to take the place of the metal parts in his acetone-soaking jig. They should arrive tomorrow.

So, we will be begin the venting process tomorrow. Doors to come off on Tuesday.

12240   Mon Jul 4 10:30:37 2016 ericqUpdateGeneralPreliminary vent plans

Here are some plans / rough procedures for this week's vent. It is unlikely that I have though of everything, but this should be a reasonable starting point.

The mode cleaner still hasn't been locked in air, we may not want to touch the Y arm optics until we are able to lock to the Y arm and dither align, so we are sure to keep the input pointing from drifting away too much.

# Primary objectives:

• Re-suspend ETMX
• First contact of all arm cavity optics

# Secondary objectives:

• Install new gauges
• Replace 40mm baffles with 50mm baffles
• Check cleanliness of inner viewport surfaces

# ETMX project

• Open ETMX chamber
• Take all manner of photos of ETMX suspension in-situ
• If some kind of obvious issue is evident, fix it, proceed accordingly
• Mark suspension position
• Move suspension to edge of the table, more pictures + inspection
• Move suspension to flow bench, remove optic
• Transport optic to clean room
• Acetone soaking / standoff removal
• Re-glue side magnet
• Re-glue guide rod + standoff
• OSEM transplant from old to new suspension
• Suspend, following SOS suspension procedure
• Drive optic around, see if jumps are evident
• Clean with first contact
• Reinstall optic, align, etc.

# Optic cleaning

For \$optic in [ITMX, ITMY, ETMY]:

• Open chamber
• Take many, many pictures
• Mark suspension position
• move suspension to edge, take pictures of HR surfaces
• Mark OSEM orientation, remove oems
• Clean AR and HR surfaces with first contact
• Reinstall OSEMS at proper position, rotate to minimize bounce/roll coupling
• Reinstall optic, align, etc.
12243   Tue Jul 5 17:14:02 2016 ericqUpdateGeneralVent progress

Rough summary of today's progress:

• IMC locked, reasonably aligned. (Only have MC2 trans reference, no WFS)
• FSS Slow lock threshold got lowered to 1k MC2 trans
• Autolocker doesn't really work, though I made some modifcations to it that reflect the manual locking that works
• TTs, PRMI optics moved around until AS and REFL spots looked good.
• Small flashes visible in TRY
• ND filter on Y transmon QPD removed, since we have so little light
• Y arm was not locked, but this was deemed suitable to proceed
• Heavy doors taken off ETMX and ITMX chambers, light doors put on.
• Went into ETMX chamber, poked around, took a bunch of pictures (Gautam is uploading has uploaded to picasa (foteee account), the two best ones of the stand-offs on either side are attached, although I guess we can't really conclude anything from these except that on the side with the OSEM, there seems to be a few extra stray bits of epoxy residue...)
• Removed ETMX side OSEM to get a picture of that side of optic (it is currently off, ETMX watchdog shutdown for now...)
• Checked that table is level with clean spirit level (it was to within the resolution of the spirit level which is quoted as 0.42mm/m)

I didn't really see anything out of the ordinary on the ETMX suspension. Earthquake stops had clearance, OSEMS were secure, no visible glue degredation on face magnets. Inspection with green LED flashlight didn't reveal any obscene dirtieness on either face, just a few particles here and there. The top of the opic barrel unsurprisingly has a good amount of particulate. The wire grooves are way too small to resolve anything at this point, other than that they exist.

The suspension footprint is already marked, tomorrow we can move the suspension closer to the door to get an even closer look at it, before removing it from the chamber.

Attachment 1: noOsemSide.JPG
Attachment 2: OSEMside.JPG
12246   Tue Jul 5 21:51:35 2016 ericqUpdateGeneralVent progress

One glitch was seen to occur without a change in the output voltage monitors in ELOG 11744

12263   Thu Jul 7 00:25:07 2016 ericqUpdateGeneralVent progress - ETMX SUS Coil driver electronics investigation

It may be advantageous to look at the coil output data from when the OSEM damping is on, to try and reproduce the real output signal amplitude that gets sent to the coils.

12268   Thu Jul 7 15:23:39 2016 ericqUpdateGeneralSUS Vmon

Based on Koji's observation of a flat TF, it seems more likely the Vmon channels are looking at the path I've highlighted in green (named "EPICS V Mon"), rather than the path in red (named "DAQ Mon") that Koji initially suspected. This path still lacks any AA for the 16Hz EPICS sampling.

12274   Fri Jul 8 14:03:26 2016 ericqUpdateGeneralETMX removed from suspension

ETMX is currently in the clean room, the barrel is the tiniest bit submerged in acetone that will remove a guide rod, standoff, and side OSEM.

Additional inpsection of the standoffs on the flow bench did not provide any insight, pictures are in picasa. Here is a cropped version of a picture we took:

We should look at them under a microscope.

12276   Fri Jul 8 16:33:26 2016 ericqUpdateGeneralETMX removed from suspension

The magnet, guide rod, and standoff came off without too much force. However, some epoxy residue remains on the barrel. I didn't really want to scrape it off, so I've opted for more soaking. Much of the acetone had evaporated already, so I put some more - just to the point where the residue is submerged.

12283   Sun Jul 10 15:38:01 2016 ericqUpdateGeneralETMX in guiderod/standoff gluing fixture

I was hoping to glue a standoff and guide rod today, but some problems have reared their heads. Story follows:

Upon first placng the optic into the standoff gluing fixture, I was presented with a geometric problem. In the assembly procedure, one glues the rods before the magnets, which prevents a situation like this:

When what you want to do is this:

So, I spun the optic around such that the magnet is on the far side of the scribe line from the side arm, and instead of extending the side arm past the scribe line, will bring it back towards the near side. I also swapped the arms of the fixture such that the guide rod will be glued on the opposite side of the optic than the side magnet, so the side magnet won't get in the way when doing the pitch adjustment of the second standoff.

Then, I found the scribed ruby rods, and took a look at one under a microscope. The groove looks nice and sharp. I placed the standoff in the side arm of the fixture.

However, the fact that the groove does not go all the way around the standoff leads to problem #1: when adjusting the position of the side arm, the standoff seems to roll around unpredictably, making it hard to deterministically position it while keeping the groove facing outwards.

Problem #2 is not too surprising give Steve's finding about the guide rod holding arm in ELOG 12264. Given that the tip is banged up, the guide rod does not sit straight in the arm, making it crooked. This would lead to the second standoff's groove not being well aligned to the suspension wire.

I will meditate on solutions to these problems... I have covered the optic and fixture with the same foil hut Koji made on Friday.

Also, I peeked at the aluminum standoffs under the microscope. Since the groove goes all the way around, we don't really know where the wire was seated before. Still, there are some places where the groove looks kind of worn:

12284   Sun Jul 10 15:54:23 2016 ericqUpdateCDSAll models restarted

For some reason, all of the non-IOP models on the vertex frontends had crashed.

To get all of the bits green, I ended up restarting all models on all frontends. (This means Gautam's coil tests have been interrupted.)

12285   Sun Jul 10 17:33:00 2016 ericqUpdateGeneralVent progress

It took a little time, but I relocked the IMC and realigned to the point where the PRC is flashing, visible on REFL and AS, and tiny flashes are visible in TRY.

12290   Tue Jul 12 09:18:12 2016 ericqUpdateGeneralSlippery substance mystery

I found a note on Steve's desk that R. Abbott left yesterday afternoon about an unidentified slippery substance being present on the floor by cabinet S12, along the X arm. (Steve is away this week)

Just now, I found no trace of the substance in the vicinity of that cabinent (which is one of the cabinets for clean objects). Maybe the janitor cleaned it already?

12292   Tue Jul 12 16:08:00 2016 ericqUpdateGeneralETMX ruby guided gluing

[ericq, Koji]

We have positioned and applied epoxy to one ruby standoff on ETMX, for overnight curing according to the SOS standoff gluing procedure. This included:

• Removing and reinserting the guiderod until the groove is properly oriented, as seen by microscope
• finding the right vertical offset with the microscope + 3 axis micrometer stage
• axial centering by equalizing the distances from the grove to each bevelled edge of the barrel with the microscope stage
• mixing epoxy
• Testing the mix by putting some drops on some foil, and putting that in a 200F oven for 15 minutes, and checking that it cured well
• Applying some tiny droplets of expoxy using the tip of some copper wire, making an effort to keep epoxy away from the glue

Instead of trying to fix up a way of gluing the guiderod with the proper alignment, we chose to be more conservative and glue the standoff today, then switch the gluing fixture's arms tomorrow to glue the guide rod with the good fixture arm.

Additionally, we chose to glue one of the more assymetric standoffs on this first side. What I mean by this is: We have 3 ruby standoffs with grooves. Two of them have the groove about 1/8th of the way along their length, and one has it about 1/4 of the way. Since the second standoff is going to be glued while suspended, after pitch balancing, we figure that we want to use the more centered groove on that side, meaning we used one of the 1/8th standoffs today.

Unfortunately, we neglected to take any pictures :/

12316   Wed Jul 20 14:03:01 2016 ericqUpdateSUSEffect of thicker ruby standoffs

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.

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:

$\frac{\omega'_\theta}{\omega_\theta} \approx \sqrt{\frac{b'}{b}}$

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:

$b' = b - \frac{\oslash_{\textrm{ruby}}-\oslash_{\textrm{Al}}}{2}$

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.

12322   Thu Jul 21 17:01:59 2016 ericqUpdateGeneralETMX magnet gluing/guiderod excess glue removed

One step forward, two steps back...

While attempting to suspend ETMX, I broke off a side magnet

It is now gluing

(This is *not* the one that was previously glued. I.e., now both ETMX side magnets have been reglued)

12328   Sun Jul 24 03:43:56 2016 ericqUpdateGeneralMagnet positioning

When Koji and I were gluing magnets to ETMY, we decided to position the side magnet based on the empirically observed offsets from the standoff groove seen at other side magnet locations. Specifically, we figured that the magnet should be glued 1.25mm closer to the HR surface than the wire groove.

However, Steve has told me that he believed that this distance should be something like 0.5mm.

I used the 1.25mm figure when gluing the ETMX side magnets, which now do not align well to their OSEM mounts. While it is certainly possible that I made an error when shimming the fixture, I think it is also possible that this figure was incorrect.

Sadly, after poring through the DCC and various elogs, I have not been able to come up with a definitive answer on what this offset should actually be.

One approach is to examine the suspension tower dimensions. I.e. when subject only to gravity, the wire loop should lie in the plane of the back face of the top block of the suspension, as it is constrained by the clamps. Thus, the standoff grooves also lie in this plane. The center of the side OSEM mounting holes are about 1.64mm in front of this plane, which is larger than the 1.25mm figure that Koji and I came up with. Examining the picture Gautam posted of the marginal magnet/OSEM alignement, we see that this figure would in fact move the magnet in the wrong direction...

ELOGs in which the intitial side magnet gluing and fixture shimming are detailed do not reference the absolute position of the side magnet, nor do they include any pictures of their fixture setup. (Some links for the curious: 2652 2654 2668)

The DCC isn't much help either, as it is not clear what version of the gluing fixture we actually have. There is a drawing for a 40m specific version, but it includes swappable side-magnet-pickle-picker-slots to achieve different positions for different (circa 2001) optics; this is not the kind of fixture we currently have in our possesion. (https://dcc.ligo.org/D010131) I have discovered that some versions of this fixture (https://dcc.ligo.org/d990168) include an assumed 0.5deg wedge angle and thus position the two side slots differently. Although the fixture we have has no identifying marks on it whatsoever (naturally), I measured the two side slots to be different in axial position by roughly 0.6mm, which is consistent with a 0.5deg wedge. Furthermore, the sign of this difference indicates that this fixture ring is designed for the opposite wedge orientation than our ETMs, which have a 2.5deg wedge, making this fixture wrong by 3deg (which is ~4mm over the diameter of the optic).

We did not account for this for either ETMX or ETMY, so this is another source of error, but this does not give us much guidance on what the real absolute magnet position should be.

12331   Mon Jul 25 13:01:49 2016 ericqUpdateGeneralETMX suspension - progress

(Full resolution versions of the photos in this ELOG are on picasa)

The OSEM gender changers were not in the box labelled as such, we need these to be able to use the OSEMS to see just how bad the side magnet alignment is, and to do any kind of damping for the fine pitch balancing. The hunt is on.

In the meantime, Gautam and I checked out the standoff seating, and alignment of the face OSEMS (after slightly adjusting the wire length - I guess some sagging is still happening).

With a bit of poking, we convinced ourselves that we sat the standoff in contact with the optic's barrel. Amazingly, we were able to maintain the coarse pitch balance of the optic.

We then partially inserted the face OSEMS, to check their magnet alignment. ("partially" means that the OSEM is not actually enclosing the magnet, we don't want to knock anything off) They seem ok, but not perfect. These magnets were not removed or reglued, so presumably their alignments should be unchanged.

12336   Tue Jul 26 09:56:34 2016 ericqUpdateCDSc1susaux restarted

c1susaux (which controls watchdogs and alignments for all non-ETM optics) was down, the last BURT was done yesterday around 2PM.

I restarted via keying the crate. I restored the BURT snapshot from yesterday.

12345   Thu Jul 28 03:22:28 2016 ericqUpdateGeneralETMX magnets re-reglued

[gautam, ericq]

Brief summary, some pictures and such follow in the daytime.

• All magnets enclosed by OSEMS were knocked off. (This means one side magnet remained, on the guiderod side)
• Glue residue cleaned from ETMX
• Dumbbell feet were cleaned of glue, finely sanded, re-scored with a razor blade
• The magnet gluing fixture was painstakingly aligned multiple times, adjusting the shim height to get a magnet/wire groove clearance of 0.25-5mm
• Epoxy mixed, test batch cured perfectly, applied to 5 dumbbells (after triple-checking polarities) and set to glue.

The epoxy needs at least 12 hours of room temperature air curing, so no touchy until 3:30PM on Jul 28!

12351   Fri Jul 29 03:32:30 2016 ericqUpdateGeneralETMX suspended once more

[gautam, ericq]

Tonight's progress on ETMX:

• All pickle pickers removed successfully, face magnet positions look symmetric (all on border of AR coating), side magnet same location as in yesterday's photo
• Flipped around clamp blocks on winches and top blocks, refinished main clamp block not on tower yet
• Trimmed viton tips of EQ stops, I had left them too long before, leading to bending and unwanted translation when in contact with optic
• Inserted optic into bottom EQ stops, turned bolts to position optic at correct height and sort of pitch leveled
• Threaded new length of wire up through both sides, clamped at winch. Made an effort to avoid any wire twisting.
• Winched until enough tension to sit in standoff groove, inserted second ruby standoff
• Winched to just come up off of bottom EQ stops, observed neccesary correction of second standoff for rough pitch balance
• Roughly pitch balanced by iterating standoff location
• Partially inserted OSEMS, all four face magnets looked low. We figure it's more likely that our microscope was set to the wrong height, than all four OSEMS being too high by the same amount. (Given how the face magnets are all located on the concentric circle of the AR coating, we know there wasn't much translation error in the magnet gluing)
• Did some common mode winching of both wire ends to get magnets to correct height, all OSEM alignments look good
• Inserted OSEMs to half of open voltage
• Having trouble engaging stable damping of all DoFs, this will be followed up in the daytime.

Since the air bake oven we had been using is out of commision, we're not sure where to do our EP30 test runs. If we are fortunate, we can get the fine pitch balance done tomorrow while Bob is still around, so he can help us quickly bake the test dots, so we can do the standoff gluing.

12353   Fri Jul 29 03:59:55 2016 ericqUpdateSUSIn air OSEM diagonalization check

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

Attachment 1: BS_OSEM_diag.pdf
12410   Mon Aug 15 14:34:33 2016 ericqUpdateSUSSOS sus wire ordered

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.

12416   Wed Aug 17 08:47:43 2016 ericqUpdateSUSAir-bake finished

I turned off the air bake oven at 8:45AM. I'll leave the optics alone for a bit while it cools.

12441   Thu Aug 25 15:43:29 2016 ericqUpdateSUSOSEM issues

We've seen for some time now that one of the PRM OSEM signals has been gone, and all of the SRM signals seem dark. We had tried squishing various cables to no avail.

Today I played some "musical satellite boxes," in an attempt to see if the problems are in the chambers or in the signal chains. That is, I swapped the OSEM cables from the vacuum feedthroughs between the satellite boxes, and observed what happened.

It seems clear that something is up with SRM inside the chamber. For PRM, it's not so clear...

 PRM Satellite SRM Satellite BS Satellite PRM OSEMs LR low + small fluctuations LR low + small fluctuations LR low + small fluctuations SRM OSEMs No signals No Signals No Signals BS OSEMs LR low, flat OK OK

Somehow, issues with the LR channel follow both the PRM OSEMs and the PRM satellite box.

PRM LR first went dark on Jul 2nd, after the IFO was vented, but before we took any doors off (which happened on the 5th). I'm not sure what may have caused this.

SRM OSEMS first went dark on the evening of Jul 18, the day before ELOG 12310, when ITMY was moved in the same chamber. Maybe this ELOG was written about work the day before, but the sensors show disturbances over the course of hours. I think we need to double check the connections in chamber.

12447   Fri Aug 26 14:09:46 2016 ericqUpdateSUSETMY UL sensor problematic

We do indeed have a box of clean spare OSEMs, it should be out with all of the other boxes of clean stuff we had for the suspension building. You could also try swapping in a different satellite box, to see if the circuit powering the OSEM PD is to blame.

12504   Mon Sep 19 11:11:43 2016 ericqUpdateSUSAlignment status

[ericq, Steve]

ITMX is free, OSEM signals all rougly centered.

This was accomplished by rocking the static alignment (i.e. slow controls) pitch and yaw offsets until the optic broke free. This took a few volts back and forth. At this point, I tried to find a point where the optic seemed to freely swing, and hopefully have signals in all 5 OSEMS. It seemed to be free sometimes but mostly settling into two different stationary states. I realized that it was becoming torqued enough in pitch to be leaning on the top-front or top-back EQ stops. So, I slowly adjusted the pitch from one of these states until it seemed to be swinging a bit on the camera, and three OSEM signals were showing real motion. Then, I slowly adjusted the pitch and yaw alignments to get all OSEMS signals roughly centered at half of their max voltage.

12507   Mon Sep 19 22:03:10 2016 ericqUpdateGeneralFurther recovery progress

[ericq, Lydia, Teng]

Brief summary of this afternoon's activities:

• PMC alignment adjusted (Transmission of 0.74)
• IMC locked, hand aligned. Tranmission slightly over 15k. Measured spot positions to be all under 2mm.
• Set DC offsets of MC2 Trans + WFS1 + WFS2 (WFS2 DC offsets had wandered so much that DC "centered" left some quadrants almost totally dark)
• Set demod offsets of WFS1+WFS2
• Note to self: WFS script area is a mess. I can never remember which scripts are the right ones to run. I should clean this up
• WFS loops activated, tested. All clear.
• Locked Yarm, dither aligned. Transmission 0.8
• Moved BS to center ITMY reflection on AS camera
• Misaligned ETMY, aligned PRM to make a flashing PRY AS beam. REFL camera spot confirmed to be on the screen, which is nice
• Wandered ITMX around until its AS spot was found. ITMX OSEMs not too far from their half max. (todo: update with numbers)
• Wandered SRM around until full DRMI flashes seen
• Centered all vertex oplevs
• Made a brief attempt at locking X arm, could only get some crazy high order mode to lock. BS and ITMX alignments have changed substantially from the in-air locks, so probably need to adjust ETMX much more.

Addendum: I had a suspicion that the alignment had moved so much, we were missing the TRX PDs. I misaligned the Y arm, and used AS110 as a proxy for X arm power, as we've done in the past for this kind of thing. Indeed, I could maximize the signal and lock a TM00 mode. Both the high gain PD and QPD in the TRX path are totally dark. This needs realignment on the end table.

ELOG V3.1.3-