We were unable to fully open GV6 today after the cylinder repair. We heard the clunk of the gate camming over at 45 psi, but it did not start to raise until 55 psi, at which point we could hear air blow-by at the solenoid manifold, and up at the cylinder itself.

So we stopped trying to open the valve any further and slowly reduced the regulator output in order to bleed out the accumulated pressure on the bottom side of the piston. This lowered the gate back down and we heard the gate touch down indicating it is soft closed.

We will have to disassemble to air cylinder again and see what may be the issue. We still have 4 sets of replacement seals and one brand new air cylinder on hand if needed.

The valve remains soft closed until we are able to troubleshoot and repair the cylinder.

8/3/2026

Travis, Gerardo, Jordan

Today we again disassembled the GV6 air cylinder with the valve soft closed to try and see what may have been causing the air blow-by which prevented us from fully opening the valve last week.

We did not find anything immediately obvious such as a seal that had jumped out of the groove, so we measured the ID of the original air cylinder, which was re-used, and found that it was ~0.01" larger than the ID of the spare cylinder (original ID ~8.015", spare ID ~8.005"). We then elected to use the spare cylinder instead to make sure there is good sealing contact with the cylinder wall, so we re-distributed the grease on the new cylinder and attempted to install over the piston, but the tube seemed to be slightly out of round and would not fit over the piston. So we flipped the tube 180 degrees and measured that side of the tube and found it was better. We again added grease to that side of the cylinder and installed it over the piston, ensuring the seals and wear band stayed in place, Then we re-installed the threaded rods, torqued the nuts, installed the reed switches and installed the air lines.

To verify all the new joints/connections were ok, we put ~10 psi to the top of the cylinder and then to the bottom to see if there were any leaks. There were none so we started to open the valve by increasing air pressure at the regulator, once we got to ~25 psi we could hear and feel air coming out of the bottom plate/adapter flange below the cylinder assembly, see picture below the area where air is coming out of is circled in red, at which point we stopped trying to open the valve and closed the quarter turn isolation valve to the air line.

We spoke with a GNB rep who advised we try to to open at a higher pressure and see if the bottom seals, so we then tried to open the valve again. This time we started at 20 psi and followed our normal opening procedure with the exception of increasing by 5 psi instead of 10 and waiting 3 minutes between increases. At ~35 psi, air stopped leaking out of the bottom flange, there was no air blow-by in the cylinder and we could hear the carriage starting to move. The gate fully opened at ~48 psi and Gerardo was able to take a video where you can hear the piston incrementally move up the cylinder. We increased the holding pressure to 58 psi and verified the MEDM screen showed the valve status as green.

8/6/2026

This morning we wanted to soft close GV6 to see if the scraping/squeaking sound continued, or if grease just need to be distributed in the cylinder. Following our normal soft close procedure,we still heard the same noise as the piston moved down. 

We decide to swap the cylinder one last time to the spare cylinder which removed from GV7 back in May. This cylinder had an ID of 8.004" on both ends. 

During the removal of the "sticky" cylinder, we saw there were some small metal shavings on top of the piston, so we decided to remove the seals and install new ones to make sure there is no damage or debris that could cause sealing issues. We added grease to the new seals/o-rings, and the inside of the cylinder, then re-assembled the cylinder/threaded rods/nuts. 

An updated cylinder repair procedure in the works at E2600176.

Once we were done with the cylinder assembly we opened the gate valve to test functionality, and see if there were any leaks in the cylinder. We again heard air coming out of the bottom flange, same as the entry above, but once we got to 35-40 psi the leak stopped and we could hear the carriage moving up. This time there was no excess noise or dragging, and the valve fully opened at 48 psi. After of ~10 minutes with the valve open, and we confirmed there were no leaks in any of the newly assembled joints, we soft closed the valve, again there was no excess noise or dragging of the piston. This is what we typically see/hear when actuating the pneumatic valves.

GV6 remains soft closed for now, closing WP 13471

Videos related to alog 91378 above (original .mov files compressed to be able to upload in alog)

PSL team said that they have relockedthe PMC and i may drift in the next 24 hours.

The HEPI, ISI, and Optics have been recovered.
All SEI Guardians for all chambers has been set to ISI Damped HEPI Offline , Except HAM7 and BS. BS ISI watchdogs are tripping for some reason. 
All Optics are set to Aligned.

 

Misaligned MC2, PRM, and SRM

For reference, the Beckhoff restore tool reads:
USB Image C9900-I901 v2.1.9.47
Computer Name: BST-000f7zrg

WP 13459

The outputs of the EP1957-0022 terminal are used to enable the CHETAY, CHETAX, and the CRS lasers. The CHETA enclosures are not installed. This required the inputs to the EP1957 for the panel/doors to be shorted. Verified enable outputs were present when system was nominal. Verified enable outputs went to 0V when an e-stop was pushed. Same was done for the CRS.

To clear the error on the EL2904, a phoenix safety relay was installed. This satisfied the minimum required load.

The branch labeled 'scripted' has been merged and deleted. The link still works however (https://git.ligo.org/cds/ifo/beckhoff/lho-laser-safety/-/commit/86f4fb088fbed6ce3c0e47afcdfc756547e70416).

(Travis S., Jordan V., Gerardo M.)
HAM2 annulus system pumpdown is done, Jordan Isolated the system earlier on the week from the aux-cart, ion pump took over the pumping with no issues.  Today, taking advantage of a computer reboot, Travis and I removed the flex hoses and can turbo from the annulus system.  Aux-cart and components were moved away and stored away from the chambers.  BTW, this time we only used one aux-cart for the pumpdown process.  HAM2 annulus system is back to nominal.

HAM1 pressure appears to be dropping now.

As far as I can tell from trending Backhoff channels for the JAC heater we have been at the same set heater power all day (~0.7W).

So not sure how it was the heater causing this.

The last time we had this problem it was because we were dumping 3W of power into the heater.

Included are long term trends of the heater power set value in Watts and the JAC thermistor we use for control in degrees. I also included the HAM1 pressure.

There was a channel cut-out about 3 hours ago in all the JAC heater channels, but I assume this was something to do with the RCG upgrade.

They all went to 0 including the JAC heater guardian. Its on state is 1 and off is 20.

During the cut-out it went to 0 so should not have turned the heater control loop on.

This zoomed in picture of the time all these channels went to 0 is the second attachment.

Here is a long term trend showing the constant readback power from the JAC heater in the bottom left plot and the JAC guardian state in the bottom right.

The temperature on the JAC thermistor has been rising sharply for the last three hours.

Summary: This makes me suspicious that some Beckhoff channel cutting out caused this temperature spike and thus the pressure spike but not sure what.

After speaking with Richard I re-inserted the guillotine as I think the the camera came loose it's currently in a location where it could fall forward and hit the VP. 

After checking on the pumpdown progress at BSC6 annulus system, the rest of the components were put back, controller was reinstalled, cables were connected (power supply, high voltage, and comms cable) and the annulus ion pump was powered on, it did not take long to reach good vacuum pressure.  Aux-cart and can turbo will continue to pump the annulus sytem until it reaches an acceptable vacuum pressure.

(Travis S., Jordan V., Gerardo M.)
Late entry.
After a few days of pumping down the annulus system, on Monday 8/3/26, the can turbo and the aux-cart were removed from the annulus system at BSC6, the ion pump and annulus system are back to nominal.

We have ZM5 SN4 installed now. Original data before we changed the preloading (E2100297) had the ROC range 3.0m to 3.9m. With at 0V applied 667mD optical power, with 200V applied 508mD.

In alog 75709 we increased the preload from 20 in lb to 47 in lbs. An estimated linear increase of 65mD as according to T2300426, changing the preloading changes the optical power by 2.4mD/in.lb.The preloading should make the magnitude of the optical power larger, so it should be increased to 667mD - 2.4mD/in lb * 27 in lbs = 602mD mD with 0 V on the PZT, 443mD with 200V on the PZT. This is an estimated ROC range of  3.3 to 4.5 meters for strain gauge -5.0 to +2.6V (it's range with 0V and 200V applied). This mostly agrees with Eric's data. 

We have ZM4 SN1 installed now. Original data before we changed the preloading (E2100289) had the ROC range -19.3m to -9.0m. With at 0V applied -104mD optical power, with 200V applied -221mD.

In alog 75677 we increased the preload from 46 in lb to 75 in lb. An estimated linear increase of 70mD.  This should be increased to -104mD - 2.4mD/in lb * 29 in lbs = -174mD mD with 0 V on the PZT, -291mD with 200V on the PZT.  This is an estimated ROC range of -11.5 to -6.9 meters for strain gauge 1.0 to 8.3V. This mostly agrees with Eric's data.

I attempted to confirm these values by repeating this exercise with a second dataset from 90827.  This was an additional set of q measurements made directly after ZM4.  The idea here is that this should allow us to fit the ROC values for ZM5 only by taking these measured qs, propagating them through ZM 5 and comparing with the measurements from 90783.  Unfortunately this did not proceed as smoothly.  The fits and mode overlap values are tabulated below.  This isn't too far from the old ROC range, but the agreement between the q values isn't nearly as good as before

Rough values for ZM5:

 Mode overlap after propagating through ZM5 assuming the above ROC values.  I was mostly optimizing the y value; the astigmatism seemed to be quite different in this dataset, leading to poor x/y agreement when propagating and comparing with the other data.  

Attached is a Sw plot at SRM made using the ROCs Eric logged above, and the measured q at the input of ZM4.

The measurements seem to be systematically different from the prediction based on ROC and the input q.  I reproduced the overlaps that Eric listed above, and they are similarly above 98% for all of these (the overlap between the prediction and the measurement for each strain guage pair).  

I also made a linear estimate of the diopters per strain guage based on the ROCs that Eric listed above, for ZM4 this give -7mD/ strain guage volt (for -11m ROC at 4V SG), for ZM5 -10.5mD/ SG V (for 4.05m ROC with SG at -2V).  This is shown by the orange stars and blue + in the attached plot, there is some discrepancy with the red and brown "predicted" points (based on just the ROCs that Eric listed above and the input q), because of the nonlinearity of Eric's ZM5 ROCs.  

Continuing from Camilla's accounting of where we want the ZM4 preload to be.  

Eric's ROC values above show the range to be from -12m ROC to -9meters (this is not quite the full range but close to it), which is -170mD to -220 mD, so the range of ZM4 psams seems to be close to 50mD.  In Camille's original charachterization data before the preload change E2100289 the range was 118mD.  

If we make a decision on where we want to move ZM4 based on the OMC matching grid in the attachment to 90804, we would gues that we'd want the lower edge of the ZM4 range to be in the middle of the range.  This means we want to reduce the pre-load by 25mD,  reducing the pre-load by 10 in lbs, to 65 in lbs.  

Above, Eric found ROCs for each strain guage value that can predict our measured q's after ZM5 (90783) starting with the measured q before ZM4, where the predicted qs overlapped with the measured qs by more than 98%.  We are aiming for sqz to OMC mode matching of better than 99%, so I wondered if we can get better agreement than this with our measurement technique.  If we want to be able to set ROCs or distances based on these measurements, we want to know if they are repeatable and consistent with a model at a level better than the mode matching that we are trying to acheive.  In O4 we had squeezer to OMC mode mismatch of 2.2%, we would like that to be less than 1%.

I take the q's measured after ZM5, propagate them back to before zm4 using the guesses for ROCs and the AOIs from the finesse .yml file, and calculates the overlap with the measured q before ZM4 for each.  The sum off the mode mismatches is the cost function used to fit either vertical or horizontal ROCs.  In this version of the script, it is fitting either the vertical or horizontal data, I would like in the future to have it include both in the cost function.

These plots (horizontal and vertical) show that this fitting results in overlap between the measured beam and the forward propagated beam using the fit ROCs is better that 99.5% for all the data.  This is true when I use only the horizontal (vertical) data in the fit, and use those ROCs to propagate the vertical (horiztonal) mode.  The worst overlaps are all for points measured where ZM5 strain guage was at -4.5V, which also had the worst values of M^2 (see top left panel).  

Using these fit ROCs and the measured q before ZM4, we can propagate to the usual Sw plot on the AR side of SRM, using either vertical or horizontal data gives us an sw plot that looks a lot closer to the measured data than the guesses above.  I think this means that we can use this kind of fit data to determine what ROC we need to move us to a particular place in Sw space in the future, at least at the level of 0.5% mode matching. 

The script to make these fots and plots can be found here

I was curious to see what Sheila's improved fits imply for our hunt for the source of astigmatism in HAM 7.  Below I've tabluated some calculations for the astigmatism, which I define as the difference in focusing power between the horizontal (X) and vertical (Y) directions for ZM4/5

For ZM4

Here T is the angle of incidence (15.5 degrees for ZM4).  The total astigmatism (line 5 in the table) includes both the physical astigmatism (line 4 in the table) due to non-uniformity in the ROC of the PSAM optic as well as the astigmatism resulting from non-normal incidence.  By comparing lines 4 and 5, we see that, for ZM4, the impact of the relatively large angle of incidence is also a significant source of astigmatism.  

For ZM5

Here T is the angle of incidence (5 degrees for ZM5)

The physical astigmatism (Dx - Dy) of the PSAM optics appear to be typical of the characterization data at Caltech in 2021.  

See this presentation from Lee McCuller:  https://docs.google.com/presentation/d/12UynUfIfyXmggvRKFq-OTcJKO3U0TrhD8XnKnrJE1CA/edit?usp=sharing

And his corresponding calcuations from the raw data:  https://git.ligo.org/wieldphysics/wield-ligo-mcculler/-/tree/main/src/wield/LIGO/mcculler/mirror_maps?ref_type=heads

Implications for X/Y overlap in HAM 7:

Note:  I do my best here to calculate the expected impact of the various ZM mirrors on our X/Y mismatch. I'm fairly new to analyzing AWC optics, so take these calculations with a grain of salt.  

From this we can calculate the astigmatism-induced mode mismatch between the x and y directions due to reflection off of ZM4 and ZM5.  This can be done using Equation 23 in the following technical document:  https://dcc.ligo.org/LIGO-T1900144

I believe that one wants to take the square root of eqn 23, since we are interested in calculating a 1D overlap integral between X and Y of a single beam rather than a 2D overlap between two separate beams.

We use the following paramters in Eqn 23:

 w = beam spot size on ZM4 or ZM5 (roughly 1 mm and 2 mm respectively)

D = difference in defocus between X and Y for either ZM4 or ZM5 (Just the last line of the two tables above)

I find roughly that |k₀₀|² = 0.997  for both ZM4 and ZM5.  The impact is small and, because the astigmatism appears to have the opposite sign for each optic, the effect of ZM4 and ZM5 will probably cancel one another to some degree (this should be straightforward to calculate, I just haven't done it here). This suggests that the impact on our X/Y overlap due to the astigmatism on ZM4 and ZM5 is likely not a significant limit to our squeezing level at present.  I'll take a look at the raw q values later to see if they tell a consistant story, will hopefully confirm that these back-of the envelope calcs using this T-doc are reliable.  

However, our measurements on SQZT7 suggest that we do have noticible astigmatism.  ZM2 seems like a more likely culprit due to the larger beam spot size on that optic (w = 2.5 mm).  

Rough estimate of the impact of ZM2:

Based on Lee's analysis of the Zygo data for the ZM2, ZM4, and ZM5 PSAMS, it appears that 10-20 mD of astigmatism is typical near the center of a PSAM optic.

For 10-20 mD of astigmatism from ZM2 with w =2.5 mm, the mode overlap between X and Y would lie between:

|k₀₀|⁴ = 0.9916 to 0.9671  

I dont think that this naive calculation where I square the result for a double-passed optic is correct in general for a retroreflected path, but my intuition is that this should be roughly right in our case because ZM2 actuates mostly on the beam defocus at FC1.  I'm not that confident in my intuition, so I plan to confirm this with some finesse modeling.  

This might account for the astigmatism measured on SQZT7.  Further measurements before/after ZM2 would allow us to confirm this theory.  

Camilla and Eric realized that the AOIs listed in the ligo-commissoning-modeling repo for the ZM2 were a factor of 2 too large, ie they were the angles between entering and exiting beams.  I've corrected this in the repo, and re-ran the fitting to the ROCs, (and cleaned up the code and plots a little). 

In the plots, all the stars are for vertical qs, all the circles are for horizontal qs.  The first plot shows the measured q before ZM4 compared to the qs measured after ZM5 propagated back to before ZM4.  If the measurements and fitting were perfect these would all line up at the horiozontal and vertical measured qs.  

The next plot shows the qs measured after ZM5, but propagated to SRM, the salmon points are the measured qs.  The dark blue symbols are predictions based on the ROCs that I fit using only vertical q measurements and the measured vertical q before ZM4, the teal symbols are based on fits made using only horizontal qs.  You can see that in the middle of the ZM5 range, the fits do a pretty good job of predicting the measured qs, but at the edges of the range the predictions are not as good.  If you look at the vertical fits, they don't do much of a worse job predicting the horiztonal data than the vertical data, so I think this means that whatever is preventing good fitting there is a larger impact than the astigmatism.  The third plots shows similar information, as a grid of overlaps between the predicted and measured qs: the horizontal fits don't do much worse at explaining the vertical data than the horizontal, and vice versa.  So, I don't have a lot of confidence in this technique as a way of measuring astigmatism,as the fitting is limited by something else. It does re-affirm that our measurement technique should be good enough to get lower than 1% mode mismatch. 

Recreating Eric's tables from above, with the corrected AOIs.  For ZM4, the astigmatism expected based on AOI alone is about 5mD.

For ZM5, the astigmatism expected from the AOI alone is about 10mD, we do not seem to need much astigmatism from the optic quality to explain the data.  

Utilmately these number's aren't very different from what they are in Eric's tables above after the AOI fix, the main difference is the total astigmatism from ZM5 which was inflated above because of the too large AOI.