Yesterday during maintenance Tuesday the pre filters for corner station LVEA HVAC units SF1, SF2, SF3, SF4, SF5, and SF6 were all swapped out for new ones. The new batch of pre filters Bubba ordered that were used in replacement are MERV-13. Which is a step up in more filtration by a factor of +2 from MERV-11 that the previous pre filters were. 
The pre filters at EY, MY, EX, and MX Supply Fan units, were all swapped out for new ones as well. These were replaced with older style but new MERV-11 level filtration pre filters. Unlike what was used to replace pre filters at the corner station LVEA units.

Summary:  This investigation tested the recent hypothesis that the MC baffles in the input arm, particularly the one by HAM3, were producing noise in DARM (74175). I found strong support for this hypothesis:  the varying amplitude of baffle motion from beating shakers matched the variation in DARM, and the velocity of the baffles measured with the laser vibrometer could roughly predict the scattering shelf cutoff in DARM. I think that we can be reasonably confident that improving these baffles during the break will result in gains of a few Mpc, and, by removing noise,  make it easier to investigate the mystery noise band.  I think the baffles are not angled enough and they retro-reflect light scattered from certain optics.  The SLiC group and others are developing hardware and techniques to increase the angle of the baffles, patch bad spots, and increase their damping.

Introduction

We have shown that shutting down air conditioners in the corner station electronics bay when they run at 13.1 Hz, removes broad peaks in DARM at multiples of this frequency, improving range by 2 or 3 Mpc (74677, 73430). I have recently found that shaking of the input arm couples strongly to DARM at 13.1 Hz and 15.2 Hz, and that vibration increases at single-frequencies between about 12 and 18 Hz, by as little as a factor of two, can produce upconverted noise in DARM (74175). This makes this region also a likely source of more broad-band coupling of the CS HVAC and the ambient vibration background in this band.  I suggested that the coupling  was through scattering off of the MC baffles, most likely the one by HAM3.  We have been tentativly planning on working on these baffles during the January break if they are confirmed as the source of this noise, the purpose of this investigation.

Laser vibrometery: MC baffle by HAM3 has resonance at 13.1 Hz,  MC tube has axial resonance at 15.2 Hz and MC baffle by HAM2 has resonance at 18 Hz.

Figure 1 shows spectra from accelerometers and the doppler laser vibrometer when it was pointed at the different MC baffles, confirming that the baffle by HAM3 has a 13.1 Hz resonance. I had to shake the input arm broad-band in order to make the motion large enough for the laser vibrometer. The figure also has photographs of the vibrometer beam spot on the baffles. I checked the calibration of the laser vibrometer by shining it beside an accelerometer on the beam tube. 

Single frequency investigations:

18 Hz – Beating shakers point to dominance of HAM2 MC baffle scattering at 18 Hz, velocity predicts scattering shelf edge, noise in DARM starts at about 5 times the 18 Hz vibration background: In order to determine if we should work on the baffle by HAM2 (strongest resonance at 18 Hz) in addition to the one by HAM3, I investigated whether the DARM noise from 18 Hz shaker injections was coming from the baffle at HAM2, or the one at HAM3, which also moves at 18 Hz during the injection. Figure 2 shows that both the beating shaker phase and the predicted shelf cut-off are consistent with coupling at the HAM2 MC baffle but not the HAM3 baffle. For my 18 Hz injection, the HAM2 MC baffle was moving about 230 microns per second, which predicts a scattering shelf cutoff of about 640 Hz, while the cutoff in DARM was at about 500 Hz, reasonable agreement. By slowly decreasing the shaking amplitude, I estimated that an increase in ambient at this frequency by about 5 would produce noise in DARM. There are many transients that can reach this level, and there may also be off-resonance coupling,  so I think we should also work on the baffle by HAM2.

15.2 Hz – HAM2 and 3 MC baffles move about the same, was unable to determine which one dominates noise: The 15.2 Hz resonance is actually a beam-line resonance of the MC beam tube and so both baffles were moving about the same amount and I couldn’t distinguish between them by the shelf prediction. Unfortunately, I was also not able to distinguish between them with the beating shaker technique because my data were swamped by scattering from a 76 Hz resonance (the shaker was making higher harmonics). I was not able to eliminate this higher frequency shaking because one of the shakers broke down and I used a speaker as a shaker (which produced higher harmonics).

14.1 Hz – in between resonances, noise in DARM starts at about 3 times the 14.1 Hz vibration background: Figure 3 shows that noise starts appearing in DARM when vibration at 14.1 Hz is increased by about 3 over background. Since there is coupling over a 12-18 Hz band, a broad band increase of less than this would increase the velocity enough to show in DARM. As pointed out in (74175), this off-resonance coupling may be currently limiting DARM and be a source of broad-band HVAC coupling.

13.1 Hz – velocity of HAM3 MC  baffle predicts DARM scattering shelf edge much better than velocity of HAM2 baffle – noise currently in DARM : The CER fans that cross 13.1 Hz increase motion of the MC tube by only a factor of 3 or so, strongly affecting DARM (73430), and my injections showed that at 13.1 Hz ambient noise levels may be limiting DARM at 13.1 Hz. For my larger injections, the vibrometer indicated that the sampled point on the baffle reached 120 um/s RMS, predicting a shelf cutoff of about 340 Hz, while  the actual shelf cutoff was at about 450 Hz. So the part of the baffle doing the reflecting must be moving a little more than the point measured by the vibrometer. At 13.1 Hz, the motion of the MC baffle by HAM2 was more than an order of magnitude lower than the HAM3 baffle, excluding it.

When I return, it would be interesting to complement these single-frequeny injections with broader-band injections that could better determine the current contribution of ambient vibration to DARM.

Suggestions for mitigation

Figure 4 shows that the 5 degree angle of the baffles is small enough that some parts of the baffle are normal to scattered light from certain optics. The photographs in the figure, taken in 2017, show the retro-reflected light from the baffles at these optics. Betsy, Alena, Calum, Eddie, myself and others are working on the following mitigations:

1) Increase the angle of the baffles

2) Increase the damping of the baffles (Qs are now in the tens)

3) Attach small baffle panels to cover any remaining retro-reflective regions of the MC baffles

4) Reduce the buckling of the panels (74175), possibly by leaving out some bolts

5) We may eventually want to consider installing nozzle baffles where there are blanks, because of the 15 Hz resonance of the beam tube

TITLE: 12/13 Day Shift: 16:00-00:00 UTC (08:00-16:00 PST), all times posted in UTC
STATE of H1: Corrective Maintenance
OUTGOING OPERATOR: TJ
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 8mph Gusts, 6mph 5min avg
    Primary useism: 0.02 μm/s
    Secondary useism: 0.25 μm/s
QUICK SUMMARY:

IFO is attempting to relock after ADC card failure in h1iopseib3. Erik, Richard and TJ worked on this about an hour before shift and got everything up and running again. See alog 74774 for details. EX seems misaligned (due to a trip) so may go through initial alignment if this lock attempt doesn't work.

Currently locking ALS though TJ mentioned lower ALSX/Y arm transmition than usual (by about 0.1/0.2 counts) - a weeklong issue apparently.

Looks like the lock loss was caused by an ADC error on h1iopseib3. Erik is currently working on the issue.

Gabriele, Sheila, Artem, Louis


Since Gabriele found low frequency noise (~4 Hz) non-linearly coupling into DARM at higher frequencies (~15-25 Hz) (see LHO:73937), Sheila & I have been working to prop up a dependable model of the DARM loop that can be used to estimate stability margins and offload actuation from ETMX L3 to L2 and L1. N.B. we're not 100% certain that the noise we're chasing is due to the ETMX ESD.


1. The DARM Model
To estimate DARM loop stability, we've been primarily looking at modeling and directly measuring IN1/IN2 at the input to each stage's LOCK bank filter. IN1/IN2 at the input to the L3 LOCK bank filter (often measured as (IN1/EXC)/(IN2/EXC) so as to not be biased towards 1) is the open loop gain, G, of the DARM loop. We've been calling IN1/IN2 measured at the input to the L2 and L3 LOCK banks Gp and Gu, respectively. This is because they each behave somewhat like an effective open loop gain as measured at those points in the offloaded DARM loop. Similar to G, Gp, and Gu (the "OLGs"), we calculate the loop suppression, 1/(1-G), and the closed loop gain, G/(1-G), for each our three test points (G, Gp, and Gu) at the input of each ETMX LOCK bank filter.






Figure 1 above is a Bode plot of G, Gp, and Gu for the LHO DARM loop overlaid with measurements taken for G and Gu. The OLG, G, measurement was taken from a recent calibration swept sine and the measurement of Gu is courtesy of Sheila from LHO:74226. The two measurements shown for G and Gu match the model pretty well. There is some noise in the Gu measurement but the structure is in pretty good agreement between the model and the data. The measurement of G also matches pretty well but begins to deviate below 10 Hz. This is likely in large part due to error in fitting the sensing function, C, at low frequencies. It's worth noting that the UIM stage has multiple UGFs just below 2 Hz and 4 Hz; this is okay but not ideal.

We tried taking a measurement of Gp but we've been unable to get good agreement between the current DARM loop model and these measurements (this is mentioned in LHO:74264). We've only tried relatively low coherence measurements so far in this current sprint so we plan to get some better measurements of this soon to compare against the model. However, it's worth noting that the PUM has been a bear to model properly for a while (see for example the PUM discussion in LHO:63450). A few years ago Jenne successfully modeled length-to-pitch-to-length cross-coupling that matched data taken at the PUM stage (LHO:48738). In light of the recent modeling push, Sheila and I are have begun working to follow up on this work to include yaw in the hopes of modeling and suppressing this effect from coupling to DARM. More on that later as our current major goal is to reduce ETMX actuation as introduced at the top.

The Gu points in Figure 1 were calculated from a measurement of IN1/EXC at the input of the L2 stage LOCK bank filter. Direct measurement of Gu = IN1/IN2 was difficult due to low coherence. The relationship between Gu and IN1/IN2 is Gu = (IN1/EXC)/(1+(IN1/EXC)). See Section 4 of DCC:LIGO-T2300436 for a discussion on that relationship.

2. Comparison of LHO and LLO DARM Models

Here is a quick comparison of recent DARM loop models for LHO and LLO. 

For searching purposes I'm writing their modeled OLG UGFs:
LHO UGFs:
  1: 70.45 Hz, 26.97 degrees
LLO UGFs:
  1: 78.75 Hz, 35.89 degrees











The DARM OLG magnitudes between LLO and LHO differ at low frequencies by roughly 3 orders of magnitude near 1Hz. Here's an even higher zoom near 1Hz: LHO_LLO_comparison_OLG_super_zoom_low_freq.png. As an independent check into whether that makes sense, Artem pulled up the external disturbance sent to each actuation stage at both sites using CAL-DELTAL_CTRL_{UIM,PUM,TST}_DBL_DQ and saw that they're similar between LLO and LHO (direct link to this plot). Then he looked at the LHO and LLO error signals and found a discrepancy of 2 orders of magnitude in the expected direction (direct link to this plot). So that all seems to roughly track, which is great news. See LHO:74744 for Artem's discussion.







3. Instability of 4.5Hz boost filter not predicted by DARM model
In LHO:74226, Sheila tried engaging a L2 LOCKL FM2, "boost4.5", which caused a lockloss. She successfully engaged the boost without a lockloss the day before just before the Tuesday maintenance period. 

Here is a comparison of the LHO model with and without this boost engaged.






The hope was that we would look at the model with the boost included and be able to confirm that the resultant loop configuration is unstable. However, we aren't able to point to anything that obviously indicates that that's the case. The corresponding loop suppression plot shows some peaking near 10Hz but nothing that would have us consider it a smoking gun.


=====

So the DARM modeling efforts are progressing but there is still much to do..

TITLE: 12/13 Eve Shift: 00:00-08:00 UTC (16:00-00:00 PST), all times posted in UTC
STATE of H1: Observing at 158Mpc
INCOMING OPERATOR: TJ
SHIFT SUMMARY:
00:27 UTC HWS was restarted and took us out of Observing by making SF changes for a minute. The HWS Engineer making the changes was still in the control room and managed to handle the SDF changes which allowed us to get back to Observing.  See Alog : https://alog.ligo-wa.caltech.edu/aLOG/index.php?callRep=74770

00:29 UTC OBSERVING was reached again.

After this a small earthquake rolled through which we survived, but otherwise the night was quite.
Everthing went smooth like butter.

LOG:
No log

TITLE: 12/13 Day Shift: 16:00-00:00 UTC (08:00-16:00 PST), all times posted in UTC
STATE of H1: Observing at 156Mpc
OUTGOING OPERATOR: Corey
CURRENT ENVIRONMENT:
    SEI_ENV state: CALM
    Wind: 5mph Gusts, 3mph 5min avg
    Primary useism: 0.02 μm/s
    Secondary useism: 0.33 μm/s
QUICK SUMMARY:
H1 Is locked at NOMINAL_LOW_NOISE and OBSERVING for the past hour.
Violins lookin great!

TITLE: 12/12 Day Shift: 16:00-00:00 UTC (08:00-16:00 PST), all times posted in UTC
STATE of H1: Preventive Maintenance
INCOMING OPERATOR: Tony
SHIFT SUMMARY: Relatively light maintenance day followed by some trouble getting locked, but after adjusting thresholds in ALS Guardians, was able to lock without much issue.

• 16:07 Lockloss from commissioning test, ISC_LOCK to IDLE
• 20:27 Maintenance finished, starting initial alignment
  • Troubleshooting lower ALS power
  • Manual-ed ALS Guardians to find IR; see alog74766
  • Rest of locking was fully automated
• 22:51 Reached NLN
• 22:55 Started observing

LOG:

Ryan S, Jenne D, Sheila

The ALS_COMM and DIFF nodes will check on the green arm transmission when finding IR to ensure that the arms are aligned well enough to move on. This threshold has been set to 0.75 but I lowered it to 0.65 since we've ran into this threshold as few times in the last week and have been unable to improve the arm transmission.

Last week this happened on Thursday (alog74655) and I just manualed around the state to continue locking. It worked for that lock to get us back up, and then it wasn't a problem with future locks until today. Today, the arm transmission was low for both arms so we went to confirm that there was no PR3 movement, and then we restored optics back to the start of the previous lock. This also didn't help. Looking at the arm power over the last few weeks (attachment 1), after the PR3 and table work from last Tuesday (alog74618) it has been lower than before then but as low as we were seeing today. The current thinking is that the PR3 move last week brought our powers lower, and while the table work improved the COMM beatnote, it did nothing for the arm powers. Once the IFO gets to a better full lock alignment, this alignment tends to give us better ALS power next lock acquisition, so lowering this threshold should help us get to that point and hopefully help sequential locks.

The long term solution would be to go back on table to realign the rest of the COMM path to camera, then renormalize the arm powers so that 1 is actually our max power, then bring this threshold back to the 0.75 that it was*. Going on that table always carries rick of making things worse, so we definitely don't want to be doing this right before the holidays. We will reconvene in 2024 on this issue if it's still an issue.

*There's a comment in the guardian code that it was 0.85 from Aug 12, 2020.

Jordan, Janos

We ran the functionality test on the main turbopumps in MX and EX during Tuesday Maintenance (12/12/23). The scroll pump is started to take pressure down to low 10^-02 Torr, at which time the turbo pump is started, the system reaches low 10^-08 Torr after a few minutes, then the turbo pump system is left ON for about 1 hour, after the hour the system goes through a shut down sequence.
 

MX Turbo:

Bearing Life:100%

Turbo Hours: 120

Scroll Pump Hours: 211

EX Turbo:

Bearing Life:100%

Turbo Hours: 277

Scroll Pump Hours: 6317

Closing WP 11573 and FAMIS 24846 FAMIS 24870

TJ, Camilla. WP11574

We borrowed the Ophir PH00235 USB MSP-NS-Pyro 9/5 bean scanner from CIT. It has a PH00092 removable 7.5" FL lens on the front and is on a 500mm rail. WE checked the scanner and rail worked in the lab using our Nanoscan laptop and the Nanoscan v1 software. 

On CO2X (layout T1200007) we added three Gold coated steering mirrors just after the power control waveplate. Added a beam block panel on the back of the table. While aligning we kept ther CO2 power requested at 0.1W.  Started aligning the beam to the beamscan but didn't finish before the end of maintenance. 

We left the beanscan and the three mirrors on the table, we moved the mirror that was in the path ("A" on photo) out of the path. Plan to finish aligning and take data next Tuesday. The cables and driver boxes are in a tote labeled "nanoscan" in the TCS cabinet and the laptop is back in the optics lab cabinet.  Photos of table and beampath (nominal lighter red) attached. 

As the first part of the TW0 raw minute trend file offload, tw0 is now writing to a new area freeing up the old files for transfer. 

nds0 was restarted at 10:44 PST to serve the past 6 months of data from their temporary location as the files are being transferred to h1daqframes-0. The file copy takes about 30 hours.

This morning at 8:15am (16:15UTC) I turned off the external power supply that powered both ITM HWS CCD cameras (Dalsa 1M60), located on the floor under the HWS table.  We'll plan to check the magnetometer data to see if the 74738 comb is still present.

After we stopped HWS code and remotely turned off camera's in 74738, the DARM comb still remained. Dan, Daniel, Nutsinee expect this could be the framegrabber in the HWS computer still sending a 7Hz signal. We can troubleshoot this and how the camera's are grounded to the optics table later. 

Louis and I have been looking at increasing the offloading of the signal from the ESD to the PUM and UIM, in light of 73913. 

I have attempted a few times to make measurements by exciting at the L2 LOCK L filter, this results in poor coherence even for amplitudes that are quite large in DARM, and turning up the amplitude slightly has caused a lockloss by saturating the ESD. 

On Tuesday morning I engaged the PUM boost (L2 LOCKL FM2, boost4.5 which is a boost with a little resG aaround 4.5Hz).  Some history (with links to old alogs about this filter is here: 48767) we used to run with this boost but turned it off in early O3 because angle to length cross couplings were causing instabilities of the DARM loop.  On Tuesday morning I engaged this boost, and we stayed locked.  The first attachment shows a comparison of our ETMX drives to LLO's (LLO also uses ETMY L1 for DARM control, but I haven't plotted that here), H1's usual configuration is in gold and the time with the PUM boost engaged is in red. The ESD drive RMS is reduced by more than a fator of 2 with the PUM boost engaged.  I quickly tried a swept sine injection, and saw that the coherence was somewhat better than earlier measurements with a very small amplitude injection, so it seemed promising that we might be able to get a better measurement of the cross over with the PUM boost engaged.  

Today I engaged this boost again during commisoning time and we immediately lost lock.  The third attachment shows that turning on the boost certainly seems to be the cause of the lockloss. 

We can probably rely on the pyDARM model for the PUM crossover, since the calibration measurements validate the model above 10Hz. Today I was able to make a measurement of the UIM crossover, which Louis can use to compare to pyDARM from 1-10Hz.