[Kimura, M. Takahashi and Sawada (Hokuto)]
 We restarted presuurization of IXC up to 7.8 x 10^4 Pa with G-2 class grade air and G-2 class grade N2 on 23th/Apr.
Detailes are as followes;
1. Re-start injection the G-2 grade air into IXC
 8:34 Start injection at 3.2 x 10^4 Pa
 10:25 4.2 x 10^4 Pa
 11:34 5.5 x 10^4 Pa
 11:59 5.7 x 10^4 Pa
 13:06 6.6 x 10^4 Pa
 13:54 7.1 x 10^4 Pa 
 14:41 7.8 x 10^4 Pa.
 Stopped injection. 
2. Injection is resumed on the morning of April 24.
After completion of pressurization to atmospheric pressure, repair of flange leaks will begin.
The amount of gas used for pressurization to 7.8 x 10^4 Pa was pure air (7 m^3 x 7 bottles, total 49 m^3)
and pure nitrogen (7 m^3, 1 cylinder).

[Kimura, M. Takahashi and Sawada (Hokuto)]
 We presuurized IXC up to 3.2 x 10^4 Pa with G-2 class grade air on 22th/Apr.
The specifications of the high-purity air (G-2 grade) used are in klog-25912 for reference;
Detailes are as followes;
1. Start injection the G-2 grade air into IXC
 10:15 Start injection
 10:45 2.1 x 10^3 Pa
 11:40 6.5 x 10^3 Pa
 13:16 1.3 x 10^4 Pa
 14:50 2.4 x 10^4 Pa 
 16:10 3.2 x 10^4 Pa. Stopped injection. 
2. We will re-start injection on on 23rd/Apr. morning.

Reply to 19291. I confirmed that the designed value of open angle of the optical beams connecting PRM-PR2-PR3 is 0.02 rad.

In the attached figure, the "incident" and "exit" angles are at PR2, and are both 0.582 degs as shown. So the open angle is 0.582*2 = 1.16 deg, which corresponds to 0.02 rad.

Attached is fig2 for the original post.

[kimura]
  The parallel threaded seal joint with O-ring, which was the cause of air leakage in the valve drive of the GVitmy,
 was replaced with a regular tapered threaded seal joint.
After the replacement, a leakage test was conducted, and it was confirmed that there was no leakage.
Replacement with tapered thread seal joints is required for all KAGRA φ1000 gate valves, φ800 gate valves, and pendulum valves.
The following one gate valves are awaiting replacement.
1. GVetmy

[kimura]
  The parallel threaded seal joint with O-ring, which was the cause of air leakage in the valve drive of the GVitmx,
 was replaced with a regular tapered threaded seal joint.
After the replacement, a leakage test was conducted, and it was confirmed that there was no leakage.
Replacement with tapered thread seal joints is required for all KAGRA φ1000 gate valves, φ800 gate valves, and pendulum valves.
The following two gate valves are awaiting replacement.
1. GVitmy
2. GVetmy

The attached figure shows a summary of the current situation IMMT2-PRM-PR2. How do you think about the next step??

• IMMT2's centering is hard to be checked, though.
• Need to also check input GRX spot on the back of PR2 HR target; this spot should overlap on an IR beam reflected at PR2 toward PR3 (not input from IMMT2 to PR2). According to Fig. 3 of 29261, this spot seems also illuminate +Y side of the center line on PR2 HR target, but this should come rather miuns Y side. The target moves together with PR2 traverser, while GRX beam path won't move together with the traverser, as the steering mirror POP-POM is on the suspended table. So this might indicate that PR2 would be dislocated in the minus Y direction now. If we can somehow move PR2 with the traverser in +Y side to some extent (5 mm would be too much? then a few mm...), these mis-centering might be resolved to some extent.

[Nakagaki, Tomura, Kamiizumi, Hirose] 　Thank you very much for helping with the hard work, Nakagaki-san, Tomura-san, Kamiizumi-san.

We did cabling for the WFSf3. 
Cables were routed between mini-racks and IOO0 racks, IOO1 racks, and the REFL optical table. We did not connect them together. 
The details are summarised in the PDF file.

Future plans

• Connecting the power cable to the power strip and checking the current level of the stable power supply in the computer room. This is because the 18 V and 24 V DC power of the mini-rack will be supplied by the IOO0 rack, but when the circuits are turned on at the mini rack, it is possible that the amount of current, especially at 18 V, may exceed the limit values. For this reason it is necessary to check.

Systematic uncertainties on BS transmission and reflectivity measurements were estimated.
Updated results are:

Ts=51.9 +/- 0.2 (stat.) +/- 0.2 (sys.) % for s-pol
Rs=47.7 +/- 0.2 (stat.) +/- 0.2 (sys.) % for s-pol
Tp=77.7 +/- 0.6 (stat.) +/- 0.2 (sys.) % for p-pol
Rp=21.8 +/- 0.2 (stat.) +/- 0.2 (sys.) % for p-pol

Here, uncertainties from the incident angle and the polarization angle are considered.
It seems that they are not responsible for Rs being to low and Rp being too high, compared with the design.

Incident angle error:
 - BS and the incident beam was not aligned perfectly to have the incident angle of 45 deg. BS was in SAFE state.
 - BS reflected beam was not going though the viewport at the gate valve between BS and ITMY. The beam spot was off by ~15 cm over 3.3 m distance. From this, we have estimated that the incident angle error is about 50 mrad (3 deg).
 - Left panel of Attachment #1 is the reflectivity from the coating design, extracted from JGW-T1503347. The middle panel is the zoomed plot around 1064 nm.
 - From this, we can estimate the incident angle dependence as follows.
 - Reflectivity can be written as

R = R0 + dR/dtheta * dtheta

where theta = theta_in/n_eff is the incident angle inside the coating with an refractive index of n_eff (we used n_eff=1.7).
Slight change in theta_in introduces effective coating thickness change, which is equivalent to the laser wavelength change of

dlambda = lambda/cos(theta+dtheta) - lambda/cos(theta)
 = lambda/cos^2(theta)*sin(theta)*dtheta
 
 Therefore,

dR/dtheta_in = dR/dlambda*dlambda/dtheta*dtheta/dtheta_in
 = dR/dlambda*lambda*1/cos^2(theta)*sin(theta)*1/n_eff

 - From the coating design, dR/dlambda is -7e-3 %/nm for s-pol and -3e-4 %/nm for p-pol.
 - From the equations above, this gives dR/dtheta is -4e-2 %/deg for s-pol and -2e-3 %/deg for p-pol (Right panel of Attachment #1).
 - 50 mrad gives dR of 0.1% for s-pol and 0.006% for p-pol.

Polarization angle error:
 - When the polarization angle from s-pol is phi, the measured R will be

R = Rs*cos(phi)**2 + Rp*sin(phi)**2

 - If phi had an error of 5 deg, dR will be 0.2% for s-pol and p-pol.
 - It is hard to explain Rs being too low by ~2%, just from the polarization angle error.

Discussions:
 - Combined systematic uncertainties are 0.2% for all.
 - Rs seems to be too low and Rp seems to be too high, compared with the design.
 - The other source of error could be from the offset of the power measurements from the ambient light.
 - We could also try aligning the polarization angle by maximizing (for s-pol) or minimizing (for p-pol) BS transmission.
 

Takano, Hirata, Akutsu; following 29282.

Afternoon, we checked beam dumps, and ghost beams caught by them in IFI and IMM chambers, and all seemed ok so far. The detailed check will be done next week.

• During this work, C-2-6 blank flange of IFI chamber was detached (Figs. 1 and 2).
• To do this, call PROVIDING_STABLE_LIGHT to IO Guardian, and then zero the ASC gain so that one can walk across the light beam toward IMMT1T (see also Day 1 work: 29261).
• Useful tool: a sensor card attached to a dentist mirror
• In addition, IMMT1 should be kept without oplev feedback tentatively when checking the back of IMMT1; this can be achieved by calling PAY_FLOAT to IMMT1 Guardian.
• Do not hesitate to check REFL DC value and the relevant gige camera image when calling ALIGNED to PRM.
• Refs: invac work finalization in 2022; you can link back from 22244. Highlight would be  21655, 21654, and 21578.
• I would like to repeat that this kind of work requires at least two optical interferometer experiment experts...

Hirata, Akutsu; following 29723.

Summary

We found that the main light beam location at the aperture of PR2 HR mid baffle was almost centered when centering the beam spot on PR2 (to precisely put, PR2 HR target). This means PR2 HR mid baffle is dislocated with respect to the main (forward) beam, unfortunately. My conlusion is that this baffle needs to move about 5 mm in the minus Y direction next week.

Details

As discussed in the morning, we were worried if the current light beam was not be clipped at the aperture of PR2 HR mid baffle. So we started with checking the aperture edge with the Miyakawa-san's IR camera, and no shining in IR found. However, at the same time, we found that the beam passed through the very center (or even shifted in the minus Y direction slightly) of the aperture (Fig. 1).

Nominally, the input beam to PR2 should pass through 6.3 mm shifted in the plus Y direction with respect to the center the aperture of PR2 HR mid baffle (JGW-T1910200-v4). Otherwise the light beam reflected at PR2 toward PR3 would be clipped at this aperture. Because we have not yet determined the "nice" alignment of PR2, we could not make this light beam so far, unfortunately. So we could not check if this reflected beam would be clipped here or not. At any rate, if the input beam would be centered, or in other words, off-centered about 6.3 mm in the minus Y direction with respect to PR2 HR mid baffle, this document says that the reflected beam would be clipped, as the 2.8-sigma edge of this reflected beam is only 4.6mm away from the aperture edge.

So, we need to move PR2 HR mid baffle 6.3 mm (or let's say ~ 5mm) in the minus Y direction.

The drawback of this move is: the invac POP-POM is on the same suspended breadboard as that for PR2 HR mid baffle. When this baffle moves, the balance of the breadboard might be affected, and the alignment of invac POP-POM may also vary slightly. The invac POP-POM is steering (1) POP_FORWARD and (2) GRX to PR3, so both of them should be affected. In short, we have to repeat Day 1 work for GRX, and Day 2 work for POP_FORWARD later. Our hope is that the suspended breadboard does not have vertical springs, so the balance variation might be very small, altough this means no vertical vibration isolation for the stuffs on this breadboard.

Anyway, moving PR2 HR mid baffle will be done in the next week. Hirata-san found several tools used in the past to move this. For reference, see 19291.

Note

• By the way, it would be kind of of-course, no shining maybe due to clipping was found at the aperture edge of PR2 HR mid baffle with the Miyakawa-san's IR camera.
• During this work, we were disturbed by a strange ghost beam, and finally found that this was due to a window attached to a gate valve between PRM and PR3; this GV had been closed. So we opened it.

[Shimasue, Takano, Michimura]

BS transmission and reflectivity were measured to be:

Ts=51.9 +/- 0.2 for s-pol
Rs=47.7 +/- 0.2 for s-pol
Tp=77.7 +/- 0.6 for p-pol
Rp=21.8 +/- 0.2 for p-pol

BS transmission for s-pol is a bit too high, which might be because BS is not aligned (it is now in SAFE state).
We might need to measure them again once BS and ITMs are aligned.

What we did:
 - Followed the procedure in klog 29275 for measuring the BS transmission.
 - For BS reflection, we opened an ICF203 flange labeled HY-2-1 (Attachment #1) so that we can stick the power meter (Thorlabs S310C) from the hole (Attachment #2).

Results:
 - The table below summarizes the results

 - By calculating T = (BS transmitted power) / (incident power) and R = (BS reflected power) / (incident power), transmission and reflectivity were estimated.

Discussions:
 - We noticed that the beam reflected by BS is not going through the viewport at the gate valve. We then realized that BS is not in ALIGNED state, but in SAFE state.
 - This means that the incident angle to the BS might be off by 50 mrad (~15 cm over 3.3 m distance).
 - The measurent tells that AR reflectivity is small enough compared with the measurement uncertainties.

Next steps:
 - Estimate the effect of incident angle from the wavelength dependence from the design.
 - Re-do the measurements with BS and ITMs aligned.

[Shimasue, Takano, Michimura]

BS transmission at ~45 deg was measured to be:

50.8 +/- 0.9 % for s-pol
78.3 +/- 1.6 % for p-pol

They are consistent with the design (see, also, klog 29269 and JGW-T1503347)

What we did:
 - Assembled a tripod setup for injecting the probe beam at IMC REFL area. We had a hard time collimating the beam for a few meters with the beam size smaller than the aperture of the power meter (Thorlabs).
 - The injection bench consists from the laser source -> steering mirror -> Glan laser prism (rotated so that it transmits most of the beam, which was mostly s-pol) -> HWP -> f=-75 mm lens -> steering mirror -> Glan laser prism (rotated to define the polarization of the probe beam) -> f=300 mm lens (Attachment #1)
 - Put the power meter head on a stick so that we can stick it inside the BS chamber (Attachment #2) to measure the power of transmitted beam. IR card was also put in front of the power meter head to find the beam.
 - Brought these setup to the BS area, and put the tripod setup for injecting the probe beam between BS and PR2 chambers.
 - The alignment of the incident beam, both in pitch and yaw was tuned by eye by centering the beam on BS.
 - Measured the incident power at the injection bench, after the last lens (Attachment #3), and the transmitted power at the back of BS (Attachment #4) by holding the power meter on stick by hand. The stick was rested on a ground and/or some vacuum structures so that the head will be stable.
 - The polarization of the probe beam was tuned by eye by rotating the second Glan laser prism (OptoSigma GLPB2-10-25.9SN-7/30). When the white line is vertical, it is s-pol and when horizontal, it is p-pol. The HWP was tuned to maximize the probe beam power.

Results:
 - The table below summarizes the results

 - By calculating T = (BS transmitted power) / (incident power), BS transmission was estimated.

Discussions:
 - The measured values are consistent with the coating design shown in  JGW-T1503347.
 - The incident angle was tuned within a few mrad (beam centering error of a few cm over injection bench to BS distance of 3.3 m).
 - Mis-tuning of the incident angle by a few mrad can be converted into laser wavelength mis-tuning of a few 0.1 %.
 - According to the coating design in JGW-T1503347, HR reflectivity and AR reflectivity does not depend very much on laser wavelength, and probably we will be still be limited by the uncertanties in the power measurement, even if we tune the incident angle more carefully.

Next steps:
 - Measure reflectivity by sticking a power meter from the ICF203 flange between BS and ITMY.
 - Re-do the measurements after aligning ITMs. Use ITM reflection to more carefully align the probe beam to the BS so that the incident angle will be the same with the main beam. (But this is probably uncesessary considering the uncertainties of the power measurement)
 - Estimate systematic uncertainties from the polarization orientation of the incident beam, the incident angle etc.

[Kimura, M. Takahashi and Sawada (Hokuto)]
  In preparation for crane inspection of the EYA clean booth,
the duct side flange of EYA and the flange on the duct side opposite it were temporarily closed with stainless steel plates.
See attached photos.
 To ease the removal of the temporary flange, the temporary flange is fixed with low adhesive tape.
When removing the temporary flange on the duct side of the EYA, care must be taken with the wiring directly under the duct side flange of the EYA.

[Kimura and Ueda (SKS) ]
On the morning of April 18, a vacuum leak test was performed on the reclosed flanges around the IYC and IYA.
The results of the vacuum leak test confirmed that the reclosed flanges did not leak more than 1x10^-11Pam^3/s.

[Kimura and Ueda (SKS)]
The pressure of the X-arm increased rapidly.
Please confirm attached graph.
This was probably due to the effect of opening GVitmx and GVetmx.
Therefore, after discussing with Uchiyama, we started TMP (X-2, X-10,X-15, X-21) for X-arm and stopped the Ion pumps.
To prevent condensation on the Ion pump power supply, the high voltage of the Ion pump power supply was turned off and the power switch was turned on.

Aso, Ikeda, Hirata, Takano, Akutsu; following 29261.

Summary

Confirmed the aligned light beam POP_FORWARD reached two QPDs on the POP table, but mostly clipped at a steering mirror on the POP table. So not yet centered to these QPDs. The work is still on the way.

Details

Yesterday we tweaked IMMT1 and 2 with their oplev setpoint in yaw to their limits. So, we were worried if the actual beam might be off-centered at IMMT2. So, we started with checking this. Before that, we called PROVIDING_STABLE_LIGHT to IO Guadian to make IMC with LSC and ASC. In addition, we also set IMC ASC gain to zero (following Ushiba-kun's suggestion) tentatively from MEDM so that we were able to walk across the light beam to IMMT1T without disturbing the aligned IMC. Then, we found that the spot on IMMT2 was seemingly mis-centered somehow (difficult to see it due to the fact that it is located in the deep of the chamber and the surface is protected with the black shield). So, we re-considered our plan. At this point, the new plan was to (1) reset the setpoint values of IMMT1 and 2 to the values before yesterday, (2) check the IMMT2 centering, and if not good, adjust with IMMT1 setpoint, (3) align IMMT2 to center the spot on PR2 with setpoint, and (4) adjust PRM centering with its traverser.

When reset IMMT1 setpoint, the beam centering at IMMT2 seemed ok (Fig. 1) , so we simply left the IMMT1 setpoint as reset value. Then, we tweaked IMMT2 to bring the beam spot at the center of PR2 (precisely, its HR target); Fig. 2. With this situation, we checked the beam spot postion at PRM (both at AR (Fig. 3) and HR (Fig. 4) with the relevant targets; these AR and HR spot locations were almost the same), and it was 5-mm off-centered in the minus Y direction.

5-mm would be too large for the PRM traverser to move. The demerit of using the traverser are (1) the small movable limit itself as already mentioned, (2) we need to adjust oplevs otherwise we would lose ALIGNED state of PRM (ALIGNED state would be useful to control a suspension with its setpoint values), (3) even though "ALIGNED" can be obtained, this would not mean the beam reflected at PRM could reach REFL, and (4) at any rate, PRM mid baffles do not follow the move of the main suspension chain of PRM. On the other hand, considering the RoC of PRM is ~460 m (kagra wiki), 5-mm off center might be acceptable or easily to be compansated.

So, we determined to modify the original plan mentioned above: (4) -> not adjust PRM traverser, but adjust mid baffles for PRM later.

The PRM AR mid baffle seemingly caught two (known) ghost beams from PRM already. In this sense, this mid baffle would be also ok. But in fact, looking at the aperture of the PRM AR mid baffle, the aperture edge seemed shining with IR (Fig. 5; taken from a location between IFI and IMM with the Miyakawa-san's IR camera; two ghost beam spots at IMMT1's shield can be also seen, and they may come from IFI...). This shining might be due to the main beam's slight clipping. JGW-T1910659-v2 shows where these ghost beams and main beam would come at PRM AR mid baffle, and from these nomial locations, it would not be strage at all that this clipping might happen in the current situation: the main beam is shifted with respect to the aperture in the minux Y direction about 5 mm, while this document says the 2.8 sigma radius of this main beam should be nominally 4.8 mm away from the edge. So we will adjust the AR (and HR for balancing?) mid baffle position later. See also Fig. 6; also compare with 20797 and 21654.

Anyway, apart from the slight clipping at this PRM AR mid baffle, the main beam would be well aligned. Then, we detached the duct connecting the POP table and PR2 chamber to see the PR2 transmission IR beam, or POP_FORWARD. Fortunately we confirmed that this beam was somehow reaching relevant two QPDs (Fig. 7). We also confirmed this with QPDs SUM count variation. But we also found that this beam was 90%-ly clipped at a steering mirror just after the periscope (Fig. 8). It seemed no simple way to resolve this clipping...

Note

• We confirmed that the beam spot on PR2 varied (more than 1 mm? anyway it was apparently obvious) depending on the PRM state PAY_FLOAT or ALIGNED. Be careful when you repeat this kind of initial alignment again. I recommend to do this kind of careful alignment together with more than one interferometer optical experts, otherwise you may easily forget this and saddly your alignment would be insane.
• The way "setting IMC ASC gain zero" should be done just before such a work starts that someone would pass across the light beam to IMMT1T, maybe; otherwise, as ASC gain is zero, the alignment of IMC may become worse in the long term. By the way, we firstly did the other way but it failed: firstly we just turned on signal hold switches only for the feedback signals from IMMT1T to pitch and yaw matrices, as we thought there might not any integrators in these feedback paths. But maybe we mis-understood something; every time IMC lost lock within a few minutes.

[Shimasue, Michimura]

We are preparing a setup for BS transmission and reflectivity measurements around IMC REFL area.

Background:
 BS is designed and measured to have 50:50 transmission and reflectivity for s-polarization (Ts=49.96%, JGW-T1503347).
 But the BS transmission and reflectivity for p-polarization are unknown (Designed to have Tp=80% or so, AR for p-pol a few %, JGW-T1503347).
 To understand what is going on in the IFO for p-pol, we are planning to measure them with an another laser source during this vent.

What we did:
 - Assembled a tripod setup with a bread board to install laser source (Attachment #1)
 - Assembled a laser injection bench on the bread board (Attachment #2, now resting on IMC REFL table)
 - Assembled a tripod setup with a bar to hold a power meter to measure the incident power to the BS and BS reflected/transmistted powerr (Attachment #3)
 - We are planning to stick this power meter to ICF203 flanges between BS and ITMX or ITMY (Attachment #4 and #5)