B. Weaver, J. Kissel
WP 12109

Betsy, myself, and several others are looking to propose redlines to the WHAM3 flange cable layout (D1002874) in prep for O5 (see T2400150 for DCN and discussion there-of). 

However, in doing so, we discovered that the flange layout may have double-counted the shared cable for the MC2/PR2 M1 (top) RTSD / T1T2 OSEMs. Other drawings (e.g. the Cable Routing D1101463 and the wiring diagrams D1000599) indicate "yes, there's an extra 'SUS-TRIPLE' entry somewhere between the D6 and D3 allocation," but we wanted to be sure.

As such, Betsy went out to HAM3 today and confirmed that YES the MC2/PR2 M1 (top) RTSD / T1T2 cable, labeled "SUS_HAM3_002" in the wiring diagram or "SUS-HAM3-2" in real life, does come out of D3-1C1 and *not* out of any D6 port, and thus we validate that D6's list of 4x DB25s to support the 'SUS-TRIPLE' (i.e. MC2) in D1002874 is incorrect.

Pictures attached show the D3 flange, and highlight the SUS-HAM3-2 cable at the flange going to D3-1C1, and then the other end of that cable, clearly going into the MC2-TOP/PR2-TOP satamp box in the SUS-R2 field rack (S1301887).

J. Kissel, S. Koehlenbeck, M. Robinson, J. Warner

The LHO install team (Jim, Mitch) -- who has experience installing in-chamber fiber optic systems -- have reviewed the two options put forth by the SPI team for optical fiber routing from some feedthrus to the future location of the SPI follower breadboard on the -X side wall of the HAM3 ISI using Eddie's mock-ups in D2400103. Both options (WHAM-D8 or WHAM-D5) are "evil" in several (but different) ways but we think the lesser of the two is running the fibers from D5 (the currently blank flange underneath the input arm beam tube on the -X side of HAM3; see D1002874).

In support of this path forward, one of the primary evils with D5 is that access to it is *very* crowded with HEPI hydraulics piping, cable trays, and various other stuff. 

Here I post some pictures of the situation.

Images 5645, 5646, 5647, 5648, 5649, 5650, 5651 show various views looking at HAM3 D5.

Images 5652, 5653, 5654 show the HAM2 optical lever (oplev) transceiver, which is a part of the officially defunct HAM Table Oplev system which -- if removed -- would help clear a major access interference point.

I tested again the OMC aligment with low frequency lines, as in 76335

It looks like there is still some modulation of the DARM line amplitude at 410.x Hz. There is also some effect on the pitch jitter line amplitude, but no effect on the yaw jitter line amplitude.

New offsets that simultaneously make the DARM calibration line maximum and the pitch jitter minimum:

I put those offsets in. The range dropped. So they are not good. I don't understand why. I reverted them. The range went back. A step in the other directions did not change the range much, but KAPPAC dropped.

Very low frequency angular lines are being injected in the OMC ASC controls starting at 14:39 UTC. The longer they run the better, but please feel free to stop them if other tests are ongoing.

awggui's are running on cdsws26.

This is a test to see if we can find a better OMC alignment position, and if this has any effect on DARM noise.

Earlier today I did some 2.6 Hz sine injection in DHARD_Y (71590) to understand the upconversion phenomenon seen previously (71505). This is maybe related to the non-stationary noise in the 20-50 Hz (71092) and the observed bicoherence (71005).

In summary: DARM noise between 20 and 80 Hz gets worse for positive excursions of DHARD_Y_IN1 from zero, but not for negative excursions.
It doesn't look like it is necessaarily correlated with the 2.6 Hz peak (although that peak contains a lot of the RMS in normal conditions).
This might indicate that we have a static offset in DHARD_Y alignment.

The first atttached spectrogram shows in the top panel a DARM spectrogram, whitened to the median of a quiet time, so that a value of 1 means normal noise levels. The bottom panel shows the DHARD_Y 2.6 Hz excitation amplitude, and the DHARD_Y error signal value. The most interesting feature is that noise in DARM is higher when DHARD_Y value is positive and large, but not when it is large and negative. The second plot shows a zoom in time of the same spectrogram, which makes the correlation evident.

To better understand, I computed the DARM BLRMS in the 20 to 50 Hz region [using the spectrogram, averaged over 2-s-long windows with 1-s overlap] , and compared it with the maximum value of DHARD_Y [in the corresponding 1-s window]. The third plot shows the corrrelation and the fourth plot is a time zoom showing the clear correlation with the positive peak value of DHARD_Y.

There is a clear correlation between the DARM BLRMS between 20 and 50 Hz and the maximum positive value of DHARD_Y_IN1, but not the maximum negative value. The last plot shows how the BLRMS is correlated with large positive excursions of DHARD_Y.

Possible causes for this behavior:

• do we have a large static misalignment of DHARD_Y (maybe also consistent with the large ITMY A2L needed to reduce the coupling to DARM 71588)
• are we clipping somewhere in the output path, so when the beam moves on one side we have more noise?
• are we saturating some actuators?
• suggested by Daniel: a scattering path that depends on one of the test mass aligments

Some next useful tests:

• repeat the test at a diffferent driving frequency, to confirm it's not necessarily related to 2.6 Hz but to the signal excursion from zero
• add offsets to DHARD_Y to see if they improve th DARM noise, and while injecting a line to see if they fix the observed behavior

As a side note, the RMS of DHARD_Y is dominated by a 1.3 Hz and a 2.6 Hz peaks. The 2.6 Hz peak could be the high frequency plant resonance, but the lowest plant resonance is at 1.05 Hz (71489). Previously I showed that there is some evvidence that the test mass M0 damping could be responsible for most of the DHARD_Y motion below a few Hz (71466). So maybe another useful test would be to check the status of the test mass M0 damping, and do some noise injections to properly project the OSEM noise contribution to DHARD_Y

• Grounding check for ISC. Problem found and fixed.
• Used the viewport simulator on +X door to see if the beams (ASAIR and OMC TRANS) will come out of the viewports. They'll be fine.
• Took pictures of the table layout.
• Jim put an wafer on the table.
• I tried to take good picture of the OMC DCPD surface, but it's impossible without removing the OMC shroud, so we gave up.
• Rahul took SUS TFs and they're fine.
  • HAM5 gatevalve was closed, foil removed, and the plastic cover was put on.
• Jim unlocked ISI.
• Cleanup work by everybody.
• HAM6 ready for the door.

Some details.

Grounding.

I and Jim checked the ground loop for everything on A6 flange (ISC) again. I disconnected in-air cables from the feedthrough, put a DB25 breakout board on the feedthrough and tested the connection between pin13 (in-chamber shield) and the chamber ground.

The only genuine problem we found and fixed was a ground loop for ASC-AS_C QPD cable. Jim rerouted that cable that was bunched up under the ISI and it was fixed.

Also, when testing ground check for F1(OMC DCPD)/F2(OMC PZT)/F3(OMC QPD), disconnecting these three isn't enough. Don't forget to disconnect 3MHz cables (D4-2B1 and D4-2B2), otherwise there's this path which gives you anything from a few hundred kOhm to 4MOhm. We wasted some time because of this.

F1 in-chamber shield <-> DCPD preamp signal ground <-> RF cable SMA shield <-> SMA Rack ground -> chamber ground.

After disconnecting RF cables, don't forget to torque them using a dedicated torque wrench for SMA.

As of now, in-air cables on D6 are as follows.

AS_AIR beam position check

TJ and Tony installed viewport simulator on the +X door after adjusting the hoop positions on the real door.

From the picture I previously took (ASAIR_beampos.jpg), I know that the ASAIR beam position is about the radius of the BDV optic toward -Y direction at the BDV when it's open.

So I placed the camera so that the lens is co-axial with the line connecting the center of the ASAIR beam position by the BDV and the center of the ASAIR-AS_C splitter as good as I can (ASAIR_likely.jpg). Green cross is where I think the beam will be by BDV. Cyan line is the center line for ASAIR-AS_C BS. (Red line is the center line of the lens just so you know how big the parallax could be.)

Anyway, as far as the centering on the BS is not terrible, the beam will come out w/o any problem.

I also repositioned the camera to assess the worst case scenario (the beam will be very close to the left edge of the BS and therefore comes closest to the right edge of the viewport given the fixed position of the ASAIR beam by the BDV), and the beam will still come out of the viewport.

OMC TRANS beam check

We haven't done anything as there's no reason for a big change except that we changed how OMC ISC cables are routed inside OMCS, and that we removed OMCS suspension offsets. Just took one picture through the +Y hoop of the viewport simulator.

Table layout pictures

For posterity.

Couldn't take a good DCPD picture

I tried to take a good picture of at least one of the OMC DCPDs through the space between OMC shroud panels and through the OMC breadboard itself but I couldn't. The view is there but lighting is not (DCPD.jpg).

HAM7:

• HAM7 -> HAM5 -> HAM6 injection, alignment check and power measurement (65110).
• Rebalanced.
• Ground loop check was done, ready for the door. According to Rahul, there's a ground problem for ZM3, needs to be revisited tomorrow.

HAM6:

• New picture of OMCR DCPD shows that it probably has a cracked glass at the edge (65117). No replacement/mitigation at this point.
• Septum viewport adapter was removed (O-ring was stuck to the septum adapter plate side and had to be pulled manually by Jim).
• Septum accelerometer was put back on (see picture), cable was plugged back in, and the digital channel was confirmed to be active.
• Visual check of OSEM blade clearance was done for OM2 (because we rebalanced on Fri.). They were good. OM2 OSEMs were also recentered.
• Preliminary TF for OM1/OM2/OM3 were done while the HAM5-side purge was turned off by Gerardo (HAM6 covers were off). They looked OK but the coherence isn't good for OM1 and OM3. The purge was turned back on after that.
  • Rahul will retake TFs overnight. After consulting with Gerardo, the HAM5 gatevalve was left half-open with aluminum foil cover. That way the corner purge air mostly goes out of that and won't blow into HAM6 so the TFs will be hopefully better. HAM6 purge is on as well as HAM5 purge, so they pressurized relative to the surrounding clean room.
• Jim and Ryan worked on cable routing.
• Jim and Ryan worked on rebalancing.

What's yet to be done.

• If Raful's overnight TFs aren't great, he will talk to Gerardo to turn down the purge.
• Ground loop check for HAM6 needs to be done as some of the cables were rerouted.
• Ground loop fix for HAM7 ZM3.
• Exit photos and sweep.

Following up on Keita and Koji's converation, Sheila and I took a closer look at the OMCR DCPD in HAM6 to see if there are any cracks. We could not positively identify anything resembling a crack on the DCPD (images attached). We could also not see where the DCPD was hole punched. What is the typical size and placement for these holes? More images here. The DCPD is definitely quite dirty. We compared against some DCPDs of a similar design in HAM7 and can confirm that the OMCR DCPD is visibly much dirtier than those.

We also inspected the OMCR shroud input aperture for signs of pitting and other damage. There is no damage to report. We spent some time looking at the output aperture because we saw some potential damage along the aperture edge. After taking photos at various different angles to rule out reflections, we determined that apertures are fine, save for the occasional speckle on the shroud and the rouge edges likely left behind by the machining process. Images attached. More images here. 

We calibrated OMCR DCPD using Pcal integrating sphere. Numbers are to follow. (But note that Koji is worried that maybe the cover glass for that PD was cracked when they punched a vent hole on the diode case.)

We fixed the beam dump that was too high.

After that, we investigated the DCPD signal ground (alog 65081) and we think we know the cause of the problem but we don't have an easy fix. We'll leave it as is.

It seems that one of the cables (either PZT or QPD) that goes to the OMC breadboard was touching the OMC shroud panel. We'll revisit that in the morning, adjust that, then confirm that the laser is still hitting the OMC QPDs. If not we'll realign.

It seems that we have ground loop problem (PZT shield is connected to the chamber). We'll revisit that at some time, maybe in the morning, or maybe after we're done with the injection from HAM7 to HAM6.