J. Kissel, L. Dartez

%%%%% Executive Summary %%%%%%
Remeasured OMC DCPD electronics chain electronics, including compensation, post Jan/Feb OMC swap. There's a small, 0.3% drop in magnitude below 25 Hz. The first line of suspicion is that the environmental or electrical conditions surrounding the new style of transimpedance amplifier, even though the circuit and enclosure itself hasn't changed, but the investigation has just started.

%%%%% More Info %%%%%%

As y'all know, we swapped out the OMC in Jan / Feb 2024 (see highlights in LHO:75529). 
That means we have brand new gravitational wave DCPDs. However, it's *only* the DCPDs that have changed in the GW path. Remember, as of O4, the PD's transimpedance amplifier (TIA) is now inside a separate podded electronics box () that encloses a brand-new style of TIA (see T1900676 and G2200551). This need not -- and hasn't -- changed with the swap, where it used to need be changed because the TIA was built in to DCPDs in pre-O4 OMCs. 

So, in principle, we've "just" disconnected the old PDs, and reconnected the new PDs, to the same electronics. As such we don't *expect* the frequency response of the signal paths to change.

However, Keita reports, for the first time in history, that there're no electrical issues with the OMC sensors after the OMC swap in January (LHO:75684). While there have not been issues with the DCPDs themselves, per se, recall, for example, problems in the past including issues with shorts to electrical ground of the OMC's PZTs (IIET:12445). Keita did report that, during this Jan/Feb 2024 vent that he found and mitigated some grounding issues with the preamp though -- the 3 MHz SQZ side-band pick off of the gravitational wave DCPDs had shown some signs of electrical short to ground. Quoted from LHO:75684:
    Inside the chamber on the in-vac preamp, the DB25 shell is connected to the preamp body (which is isolated from the ISI via PEEK spacer). At first DB25 shell and the preamp body was shorted to the ISI table, but this turns out to be via 3MHz cable ultimately connected to the in-air chassis. As soon as both of the 3MHz cables were discunnected from the in-air chassis, preamp body as well as the DB25 shell weren't conducting to the ISI table any more.
I interpret this to mean that there's a *potential* that the electrical grounding on board the OMC and in the GW signal path of the TIA *has* changed from "there used to be an issue" to "now there is no issue."

So with uber-careful, precision calibration group hat on, I repeated the remote, full-chain measurements of the OMC DCPD GW path -- including the digital compensation for their frequency response -- that I took on July 11 2023 -- see LHO:71225.

Attached are the results -- the magnitude of the transfer function -- for DCPD A and DCPD B. There are three traces:
    - The former measurement with the previous OMC DCPDs, on 2023 Jul 11.
    - The first measurement with the new OMC DCPDs connected, on 2024 Feb 22 (last week Thursday)
    - The second measurement with the new OMC DCPDs connected, on 2024 Feb 26 (yesterday, 4 days later)

We do see some small change ([3.05e6 / 3.04e6 - 1]*100 = 0.3% reduction) in the magnitude below about 25 [Hz].

Preliminary investigations cover a few things that might cause this. Because of where the "wiggle of change" is happening at 25 [Hz] -- right at the RLC complex poles, I immediately suspect the environmental sensitivity of giant ~2.4 [Henry] inductors and/or the electrical grounding situation surrounding the TIA. 

Regarding the environmental situation:
    - The OMC and HAM6 are back mostly at ultra high vacuum (~1e-6 [Torr], when its typically 1e-7 [Torr]) :: (so, any physical distortions of the enclosure that would change the geometry of inductor should be similar) 
    - The TIA has been powered on for several days even prior to the 2024 Feb 22 measurement :: (so the dominant thermal load on the circuit -- the bias voltage -- should have had time to thermalize), and 
    - LVEA temperatures are stable, albiet 2 [deg C] cooler  :: (I'm not sure if a 2 [deg C] in the external environment will have such an impact on the PDs)

Of course, it's an odd coincidence that both DCPDs chain response changed in the same direction and magnitude -- maybe this is a clue.
The fact that the 2024-Feb-22 and 2024-Feb-26 measurements agree indicate that:
    - The change is stable across a few days, implying that
    - The TIA circuit has been on for a while, and circuit is thermalized

Also attached are trends of these environmental conditions during the 2023-Jul-11 and both 2024-Feb measurements.

Also also attached are the two relevant MEDM screens showing the OMC DCPD A0 filter bank configuration during the DCPD A measurement (OMC DCPD B0 is the same), and the Beckhoff switch states for the excitation relay in the TIA and the whitening gain relay in the whitening chassis.

%%%%% What's next? %%%%%%
    (1) Ask Keita / Koji / Ali some details about the DCPD chain that I've missed having been out.
        (a) Are you sure you plugged in the transmitted PD into DCPD A and the reflected PD into DCPD B, the configuration we'd had with the previous OMC?
        (b) When were the electronics powered on?
        (c) Can you confirm that other than the DCPDs and the cable connecting them to the TIA, no electronics have changed?

    (2) Using the same remote measurement, configure the system to measure the TIA response by itself to see if there's a change and if so if it matches this overall chain change.

    (3) If (2) doesn't work, use the remote measurement tool to measure the TIA and the Whitening together, take the ratio of (3)/(2) to see if the whitening chassis response has somehow changed.

    (4) If the answers to (1), (2), or (3) don't solve the mystery, or provide a path forward, then we ask "does this *matter*?" A reminder -- any change in the frequency dependence of the OMC DCPD GW path electronics that's not compensated is immediate and direct systematic error in the overall DARM calibration if not accounted for. So the question is does 0.3% error below 25Hz matter, or is it beneath the uncertainty on the systematic error in calibration that's present already for other reasons? To answer this question, we'll resurrect code from G2200551, LHO:67018, and LHO:67114 which creates an estimate of the impact on the calibration's *response* function systematic error, i.e. creating an "eta_R." 

    (5) If the resulting estimate of eta_R is big compared with the rest of systematic error budget, then it matters, and we're left no other course of action than to out to the HAM6 ISC racks with our trusty SR785, remeasure the analog electronics from scratch, fit the data, and update the compensation filters a la LHO:68167.
        

D1900451
E2100504
T1200131

HAM8 ground loops checks completed. All passed. Some cables previously modified per E2100504. This was to resolve known in-chamber ground issues for FC2 Top (BOSEM).

Description     Cable         Location               Notes
FC2 Top         FC2_001    FCES SUS-C1     Pin 13 and shield lifted per E2100504
FC2 Top         FC2_002    FCES SUS-C1     Pin 13 and shield lifted per E2100504
FC2 Middle    FC2_003    FCES SUS-C1     Tested ok
FC2 Bottom   FC2_004    FCES SUS-C1     Tested ok

Tue Feb 27 10:12:02 2024 INFO: Fill completed in 11min 57secs

Gerardo confirmed a good fill curbside.

Closes 26233, last done in 75700

Laser Status:
    NPRO output power is 1.807W (nominal ~2W)
    AMP1 output power is 67.22W (nominal ~70W)
    AMP2 output power is 141.2W (nominal 135-140W)
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN

PMC:
    It has been locked 0 days, 0 hr 6 minutes
    Reflected power = 16.3W
    Transmitted power = 108.3W
    PowerSum = 124.6W

FSS:
    It has been locked for 0 days 0 hr and 0 min
    TPD[V] = -0.01492V

ISS:
    The diffracted power is around 3.3%
    Last saturation event was 0 days 0 hours and 5 minutes ago

Possible Issues:
    FSS TPD is low
    ISS diffracted power is high

All looks nomial except for the PMC and FSS not being locked for a long duration of time, but this is expected with the ongoing in chamber PSL work.

Closes FAMIS 26487, last completed 75223

T240:

Averaging Mass Centering channels for 10 [sec] ...
2024-02-27 09:30:04.266757

There are 11 T240 proof masses out of range ( > 0.3 [V] )!
ITMX T240 1 DOF X/U = -1.057 [V]
ITMX T240 1 DOF Y/V = 0.379 [V]
ITMX T240 1 DOF Z/W = 0.496 [V]
ITMX T240 2 DOF Y/V = 0.319 [V]
ITMX T240 3 DOF X/U = -1.07 [V]
ITMY T240 3 DOF X/U = -0.485 [V]
ITMY T240 3 DOF Z/W = -1.448 [V]
BS T240 1 DOF Y/V = -0.33 [V]
BS T240 3 DOF Y/V = -0.31 [V]
BS T240 3 DOF Z/W = -0.421 [V]
HAM8 1 DOF Z/W = -0.408 [V]

All other proof masses are within range ( < 0.3 [V] ):
ETMX T240 1 DOF X/U = -0.03 [V]
ETMX T240 1 DOF Y/V = 0.005 [V]
ETMX T240 1 DOF Z/W = -0.022 [V]
ETMX T240 2 DOF X/U = -0.135 [V]
ETMX T240 2 DOF Y/V = -0.123 [V]
ETMX T240 2 DOF Z/W = -0.089 [V]
ETMX T240 3 DOF X/U = 0.022 [V]
ETMX T240 3 DOF Y/V = -0.096 [V]
ETMX T240 3 DOF Z/W = 0.026 [V]
ETMY T240 1 DOF X/U = 0.15 [V]
ETMY T240 1 DOF Y/V = 0.173 [V]
ETMY T240 1 DOF Z/W = 0.233 [V]
ETMY T240 2 DOF X/U = -0.025 [V]
ETMY T240 2 DOF Y/V = 0.21 [V]
ETMY T240 2 DOF Z/W = 0.128 [V]
ETMY T240 3 DOF X/U = 0.257 [V]
ETMY T240 3 DOF Y/V = 0.186 [V]
ETMY T240 3 DOF Z/W = 0.184 [V]
ITMX T240 2 DOF X/U = 0.189 [V]
ITMX T240 2 DOF Z/W = 0.295 [V]
ITMX T240 3 DOF Y/V = 0.193 [V]
ITMX T240 3 DOF Z/W = 0.166 [V]
ITMY T240 1 DOF X/U = 0.093 [V]
ITMY T240 1 DOF Y/V = 0.108 [V]
ITMY T240 1 DOF Z/W = 0.031 [V]
ITMY T240 2 DOF X/U = 0.082 [V]
ITMY T240 2 DOF Y/V = 0.254 [V]
ITMY T240 2 DOF Z/W = 0.09 [V]
ITMY T240 3 DOF Y/V = 0.06 [V]
BS T240 1 DOF X/U = -0.161 [V]
BS T240 1 DOF Z/W = 0.14 [V]
BS T240 2 DOF X/U = -0.038 [V]
BS T240 2 DOF Y/V = 0.061 [V]
BS T240 2 DOF Z/W = -0.11 [V]
BS T240 3 DOF X/U = -0.144 [V]
HAM8 1 DOF X/U = -0.16 [V]
HAM8 1 DOF Y/V = -0.087 [V]

Assessment complete.

STS:

Averaging Mass Centering channels for 10 [sec] ...

2024-02-27 09:31:21.264093
There are 2 STS proof masses out of range ( > 2.0 [V] )!
STS EY DOF X/U = -4.12 [V]
STS EY DOF Z/W = 2.85 [V]

All other proof masses are within range ( < 2.0 [V] ):
STS A DOF X/U = -0.505 [V]
STS A DOF Y/V = -0.796 [V]
STS A DOF Z/W = -0.601 [V]
STS B DOF X/U = 0.433 [V]
STS B DOF Y/V = 0.971 [V]
STS B DOF Z/W = -0.463 [V]
STS C DOF X/U = -0.698 [V]
STS C DOF Y/V = 0.84 [V]
STS C DOF Z/W = 0.431 [V]
STS EX DOF X/U = -0.106 [V]
STS EX DOF Y/V = 0.07 [V]
STS EX DOF Z/W = 0.038 [V]
STS EY DOF Y/V = 0.156 [V]
STS FC DOF X/U = 0.483 [V]
STS FC DOF Y/V = -0.699 [V]
STS FC DOF Z/W = 0.869 [V]

Assessment complete.

Transfer function results for FC2 in HAM8 shows that the suspension is healthy, hence we are ready to close the door of this chamber. Results for all six dof are attached below.

TITLE: 02/27 Day Shift: 16:00-00:00 UTC (08:00-16:00 PST), all times posted in UTC
STATE of H1: Planned Engineering
OUTGOING OPERATOR: None
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 5mph Gusts, 3mph 5min avg
    Primary useism: 0.02 μm/s
    Secondary useism: 0.34 μm/s
QUICK SUMMARY:

LVEA is still in LASER HAZARD
CDS Looks good
Temperatures in the LVEA Zone 4 look to be leveling out well at 67C

Today's Expected work:
HAM8 finish work and close up
More Vacuum Leak Checks and RGA scans
Possibly some OPLEV work.


 

Workstations were updated and rebooted.  OS packages were updated. 

cdsutils was updated in conda to 1.7.0 on cdsws22 and cdsws27.   It can be activated on any other workstation by running 'conda activate cds-testing'

Today's activities:
- The corner (BSC8 blanks and 1000 amu RGA GV) was leak checked, and everything was found OK - this is a big relief, as this was not anticipated - see https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=75717
- After this, the Kobelco is now shut off: https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=75980
- HAM7 pumpdown status: ~5.9E-7 Torr
- Corner pumpdown: ~4.4E-7 Torr, ~147 hours after the HV pumping started
- EX pumpdown status: 2.6E-8 Torr. The GV will remain closed during FAC works (during this week)
- At the EX RGA the bakeout temperature has been ramped up to 200 deg C
- There was an issue with the RGA connections, which has been resolved in the afternoon. Tomorrow RGA scans and possibly bakeouts will be done at the HAM7 and the OMC RGAs
- A pumping cart was connected to the GV2 annulus system, and its all-metal valve has been opened. Now it is being pumped with the cart in parallel with the AIP
- The relay tube was valved in to HAM7 (RV2 is open now)

The purge air system (Kobelco unit) was turned off this morning around 18.20 utc.  Took a dew point reading of the air at the dryer and got -42.9 degrees C.  The system was inspected daily at least once since it was turned on to support the current vent, current run hours 10,965.9.  No leaks were noted on the compressor.

However, one valve for the Pneumatech left drying tower needs to be replaced, this is a small actuated purge valve leaking dry processed air, leak is at the stem.  FRS ticket filed 30556.

Dhruva, Nutsinee, Naoki

We aligned the pump AOM and fiber. The pump fiber coupling is 43%. We also optimized the seed fiber polarization. We have ~50% of seed throughput from fiber to SQZT7. 

First we aligned the pump AOM. We set the pump ISS drivepoint at 0V and aligned the AOM to maximize the AOM throughput. The AOM throughput was 62% before alignment and is 90% after alignment. Then we set the pump ISS drivepoint at 5V and aligned the AOM to maximize the +1st order beam. After we aligned the pump fiber, the pump before fiber is 21.6mW, the pump OPO REFL is 3.05mW, and the pump OPO REFL rejected is 1.55mW with OPO unlocked. Given the 50:50 BS for SK path, the pump fiber coupling should be (3.05+1.55)*2/21.6 = 43%.

In 75951, we found that the seed launch power increases when the seed shutter is open. Today we found that it is due to the backscattered seed from the seed fiber coupler. We blocked the backscattered seed and now the seed launch power doesn't change with the seed shutter.

After opening the chamber last week, Mitch and I were finally able to get together to replace the V1 GS13, seems like the problem is probably fixed for now. First attached plot shows the passive tfs from the V1 and V2  gs13s to the tabletop Z T240. The brown trace is the old V1 gs13 before replacement, the red and blue traces are the new V1 and unchanged V2 sensor. The old V1 sensor had low response by a factor ~2 compared to the V2 sensor, the new V1 sensor now matches the V2 sensor, the V2 sensor's response hasn't changed. Prior to swapping out the sensor, we went through and checked all of the cables inside the chamber were secured, but didn't really find any explanation for the bad behavior of the old sensor.

I've done close out tfs, those seem okay, second attached image. If FC2 tfs are still okay, I think we are ready to close the chamber.

TITLE: 02/26 Day Shift: 16:00-00:00 UTC (08:00-16:00 PST), all times posted in UTC
STATE of H1: Planned Engineering
INCOMING OPERATOR: None
SHIFT SUMMARY:
The LVEA is Currently in LASER HAZARD.
Japanese Film crew was filming around the site.
Vicki, Swadha, Jenne W. were able to get the OMC locked!
A virbometer for End X was put up on the NUC32 Fom screen so we can keep an eye on it.
Jim is currently running Tranfer functions for HAM8 and will likely pass HAM8 off to the SUS team.
The Vacuum Crew has been running RGA scans and leak tests. No leaks detected. The Gate Valves will remain closed as the VAC teams continue to pump down.

 

LOG:

Today we managed to realign the cameras on HAM6 which show OMC TRANS and AS AIR.   At first we could not see any response from the AS AIR camera so there were some cable swapping back and forth, reseating of cables and a few reboots by Dave B/control room.  At some point it started working again.

In any case, beams are now on these cameras.

We found that the fan bearings in Supply Fan 1 are going bad, causing the vibrations. We switched to Supply Fan 2 and are running it in hand for now until we can get the bearings in fan 1 replaced. 

With the CDS and Beckhoff work yesterday some large numbers got into the CHILLER_SET_POINT filters which requested a low setpoint for CO2X, the laser faulted and turned of when it got to 15degC at 22:06UTC yesterday. This morning I turned it back on and set H1:TCS-ITMY_CO2_CHILLER_SERVO_GAIN_GAIN from 1 to 0 (as in alog 75715) to stop any feedback form the laser being off gong to the chiller).

TJ and I plan to make sure the H1:TCS-ITMX_CO2_PZT_SERVO_GAIN_SW2R is correctly turned on and off in the Guardian code when the CO2 lasers are taken DOWN to avoid this in future.

Rick and I cleaned the optics out here at End X.
Noted a drop in MAX Diffracted Power between M5 and the Wedged Beam Splitter from 1.1W to 1.08 W.
This may be due to the laser being turned off and not thermalized.

We would like to come back to End X and adjust the AOM alignment and we are leaving PCAL in a LASER SAFE status, LASER OFF and Key out.