[YokozaWashimi]

We moved the 3-axial accelerometer and the impact hammer from the OMC area to the IFI area.

[Tomura, Kamiizumi, Hirose]   This work was done on Friday, 26/04/2024.

Continued from klog29281.

We connected the power cables of the circuits in the mini-rack to the power strips located on the mini-rack.
These power strips are connected to the 18 V and 24 V power strips in the IOO0 rack. Then, the following process was done to check the current value of the stable power supply in the computer room.

1. First, we made sure that the stable power supply was turned on and then we increased the limit value to the maximum. Specifically, turned the knob "CURRENT" to the right to increase the limit current amount to the maximum. (The "CURRENT" knob is 3 A per 1 turn. To raise it to a maximum of 30 A, it is advisable to find the required number of revolutions from the current limit value marked on the memo, turn it by that amount and check that the knob is at its maximum and no longer stuck).
2. To check that the circuits are connected from the stable power supply, turn on each circuit and check that the 'DC AMPERES' of the stable power supply rises.
   However, because the amount of current used by the 24V is very low, the 'DC AMPERES' of the 24V stable power supply could not be visually observed to rise.
3. Switch on everything, check the current value and set the limit values. The current value of the ± 24 V remained almost unchanged, so the limit values also remained the same as before. 

   	The current value	The limit value
   +18V	24A	27A
   -18V	14A	18A

   18 V may exceed 25 A depending on circuit usage. If 25 A is permanently exceeded, the power supply should be re-examined. I would like to proceed with this for now.

I checked the reason why ETMX was oscillated.
Figure 1 and 2 show the signals of NB filters and MN DAMP filters, respectively.

DOF5 and MN_DAMP_L was oscillated at 5.1 Hz, which should be damped by DOF5.
So, it is very likely that the reason of the oscillation is DOF5 NB filter.
This filter was optimized when ETMX is at 90 K, so it is neccesary to optimize it again at the current temperature.

I requested SAFE state and checked the SDF after this work and klog29353.
Also, I turned the Pcal-X laser OFF.

I added loop_check and injection_check as Decorators in the CAL_PCAL guardian:

• loop_check: make sure that the OFS loops are open.
• injection_check: make sure that the injection SWs are OFF=open.

I added these Decorators in SAFE state and DOWN state of the guardian.

Date: 2024/4/30 early morning

I checked the Pcal-X beam positions on the ETMX, and no large change was found comparing to the last beam alignment works on 4/25 (klog29331).
Fig 1: picture on 4/25, fig 2: picture on 4/30=today.

Because of the ETMX suspension stuation repoted on klog29351, the suspension state was PAY_TRIPPED and I did not touch it, which means the Tcam picture can be differ a littlt.

Tcam direction changed a little?

I checked all TFs of PRM.
All TF seem fine though resonant frequency of GAS filter is shifted slightly.

Following is an additional note, which is not problematic.
1. BF coil DoF measurement have a larger gain than before because of the calibration factor update (klog21311 and klog21315).

I measured the spectra of PRM LVDTs and OSEMs (fig1, fig2)
All seem fine.

IMC LSC was often failed when holding the output of MCL feedback.
Since MCE actuator efficincy increased by a factor of 3 due to thechange of the magnet size, I added a gain of 0.3 at FM9 (gain) of IMC-MCL_SERVO filter bank.

I performed finer alignment of X arm with ADSs.

Followings are the procedure:

1. X arm lock with both IR and GR.
2. Engage ADSs for PR3 by using GRX PD.
3. Engage ADSs  for PR2 and IMMT2 by using IRX PD.
4. Move ITMX and ETMX so that beam spot on both mirrors are good.

Left figure of fig1 and 2 show the beam spot on ITMX before the earthquake and now, respectively.
Left figure of fig3 and 4 show the beam spot on ETMX before the earthquake and now, respectively.

After the alignment, I recoarded the good OpLev values of IMMT2, PR2, PR3, ITMX, and ETMX.

Followings are the several notes we need to check.
1. IRX beam is not hit to the X arm trans IR camera.
2. GRX beam is shifted on the X arm trans GR camera.
3. We haven't checked the beam on TMSX, so I'm not so sure ADSs work fine (at least, trans power was increased thanks to ADSs, though).
4. IRX and GRX normalized transmission is around 0.7-0.8 now. I'm not so sure this value is due to the bad alignment, bad finesse, or clipping somewhere (GV between BS-IXC, GV between EXC-TMSX, optics on TMSX, and so on).

[Yokozawa, Ushiba]

During the work, we found that the OpLev beam was clipped by te RM, so we moved injection beam and in-vac mirror slightly to avoid cipping.
After rearrangement of the optics, we performed OpLev beam centering.

Hirata, Akutsu on 26 Apr 2024; following 29342.

Summary

Checked if ghost beams were within the relevant beam dumps in IMM chamber.

Setup

The same as 29342 basically. Plus, request IMMT1 Guardian to PAY_FLOAT, as we need to check behind IMMT1 and cut/shut the oplev beams.

Details

For the reference drawing, see Fig. 1 of 21578 (finalization in 2022); but I think we would need the newer version of this...

Behind IMMT1

Behind IMMT1, there are a pick off mirror (IMMT1T-POM) and a beam dump, while there are four transmission beams:

1. Forward IMMT1 transmission. Most of this is reflected by IMMT1T-POM within the chamber, and becomes ISS beam. A part of this, or transmission of IMMT1T-POM is used as IMMT1T beam for IMC-ASC.
2. Backward IMMT1 transmission. Most of this is reflected by IMMT1T-POM as well, but to be dumped later within the chamber (shown later). A part of this would trasnmit out of the chamber throught a viewport, and should be around IMMT1T beam; hopefully properly dumped on the in-air optical bench.
3. IMMT1 AR reflection (forward); this is an IMMT1 AR reflection of "1" above. To be dumped here.
4. IMMT1 AR reflection (backward); this is an IMMT1 AR reflection of "2" above. To be dumped here.

Fig. 1 shows the beam "1" and "2" mentioned above are within the IMMT1T-POM (pick off mirror). Fig. 2 shows the ghost beams "3" and "4" mentioned above are within the beam dump.

Backward beam through IMMT1 and reflected by IMMT1T-POM

Fig. 3 shows the beam "2" mentioned above is dumped by the relevant beam dump. Due to the mirror-like surface of the structure, a vertual image of the sensor card and the ghost beam can be also seen; please not confused if there might be two ghost beams; it seems only one GB.

ISS beam reflected at the relevant viewport window

Fig. 4 shows a (actually two degenrated) ghost beam generated at a viewport window through which a beam for ISS passes. In theory there should be two ghost beams, but due to the narrow separation of the two beams, they can be caught with a single beam dump.

Note

• The other beam dumps and shields were already checked the other day. For example, see Fig. 8 of Day 6 (29334).
• Different from IFI chamber, IMM chamber is not so shining when I saw it with IR camera. By the way, interestingly, Fig. 5 shows something above PRM is shining in IR. Fig. 6 was taken after Fig. 5, and maybe these are from OSEMs. Even when we shut the PSL IR beam, these IR still there.
• For accessibility, we newly detached a blank flange D-2-4 of IMM chamber (Fig. 7)

Hirata, Akutsu on 26 Apr 2024; following 29334; also refer to some historical record in 2022's finalization Day 1, 2, 3, 4AM, 4PM, 5, 6, and 7.

Summary

Checked if ghost beams were within the relevant beam dumps in IFI chamber. Found some spread stray field but left regretfully today.

Setup

• Request PROVIDING_STABLE_LIGHT to IO Guardian, then request HOLD_ALIGNMENT to IMC Guardian.
• IMMT1 and 2 -> ALIGNED
• PRM -> LOCK_ACQUISITION so that backward light beam from PRM can be seen at the same time.
• Don't hesitate to monitor IMMT1T, POP_FORWARD, and REFL.

Details

Firstly see Fig. 1, which is the same one as Fig.1 of 21655, Day 4 in 2022.

Around STM1

Around STM1, There are four beam dumps;

• a KG5 glass behind STM1
• a KG5 glass at the +Y side of STM1
• a beam dump (nameless) located above STM1 as in 22084; made of SiC.
• a beam dump #14 below STM1; made of SiC.

Among these, the first two was not be accessible today. The 3rd one can be seen in Fig. 2, catching two ghost beams and an arch-like scattered light. This photo was taken by Miyakawa-san's IR camera without using a tripod; I holded it with my hands. IR wavelength seems assigned to be shown in violet, interestingly. Unfortunately, there seems stray light field out of the existing dumps; actually, with this IR camera, such faint scattered light fields that have not been seen by sensor cards nor IR viewers, can become clearly seen; so useful. Prepare dozens of this kind of cameras to set everywhere.

Fig. 3 shows the same scene as of Fig. 2 but taken from different viewpoint. In addition to the already-mentioned stray light, CWP1 seems shining in IR. By the way, in Figs. 2 and 3, the two beam spots on STM1 are due to forward and backward beams. Seemingly they are located not too much close to the mirror holder's edge; good. Fig. 4 shows #14 beam dump still caught a kind of ghost beam.

Around STM2

Fig. 5 was taken from behind of STM2. There is a KG5 beam dump behind STM2, and maybe caught transmitting (ghost) beam through STM2. I could not take nice photos to show that the KG5 dump catcing the ghost beams. What would be good would be that the KG5 is not so shining with IR.

Carefully looking at this photo, you can see two spots on STM2, and they should be forward and backward beams. Figs. 6 and 7 was taken from the front of STM2, which is located deep inside the chamber, and the forward and backward beam spots can be clearly seen within the holder edge. Again, there are severe scattered light fields maybe due to IFI (not the chamber's name, but the Faraday isolator itself) can be clearly seen. There might be possiblity that some of the scattered light might be due to a window on GV between MCF and IFI chambers; in Fig. 7, three beam spots can be seen on this window; from the left, these are backward beam to REFL, forward beam from IMC to STM1, and backward beam from PRM. Hopefully some of the scattered field might be mitigated after GV will be opened.

Around IMMT2

There is a KG5 beam dump behind IMMT2. Fig. 8 shows the two ghost beams are within the dump.

Beam dump #13

Fig. 9 is of beam dump #13. As shown in Fig. 1, this ghost beam won't exist if the mirror attached on IMMT2 structure would not exist. This mirror is to take out one of GWP1's ghost beams to out of the IFI chamber for monitoring the input beam alignment before IFI, but never be used at all so far. I personally guess, although making these beam paths took much efforts of us, but this kind of complexity might increase the difficulty of stray light control, so this mirror should be replaced with a beam dump, or making a shroud around IFI.

Beam dump #12

Fig. 10 is of beam dump #12. As shown in Fig. 1, these ghost beams are genereted when the "IFI pick off" beam passing through a viewport window. Again, if we discard the (so far) meaningless plan to use this pick off beam, this beam dump is not needed.

Beam dump #5

Fig. 11 is of beam dump #5, which catches a transmission (ghost) beam of a pick off mirror to reflect the backward beam to REFL table.

Beam dump #11

Fig. 12 is of beam dump #11, which catches two AR reflected (ghost) beams generated at a viewport window through which the backward beam to REFL table passes.

Beam dump #8

Fig. 13 is of beam dump #8; maybe a ghost beam generated at CWP2 by backward beam.

Around input Faraday isolator (IFI)

Figs. 14, 15, and 16 are around the isolator structure. Many ghost beams and/or scattered diffused field are found.

IFI Chamber itself

Fig. 17 shows the inner surface of the IFI chamber seems shining due to stray light field. Regretfully I could not identify from where this came today. Before O5, it may be nice to do

• Detach the unused pick off mirror, and relavant beam dumps to reduce complexity of this chamber.
• Put IFI Shroud
• (Hopefully STM1, 2, and IFI should be suspended...)

Abstract:

GRX and IRX flash were found and X arm can be locked with both IR and GR.

Detail:

1. Alignment of PR3, ITMX, and ETMX:

First, we aligned PR3 so that GRX hit the center of the TMSX GR PD by scaning PR3 alignment.
Then, I scaned ETMX good alignment so that reflection beam was hit on the GR REFL PD (ITMX was MISALIGNED state at that time).
After that, ITMX was scaned so that reflection from ITMX is hit on the GRX REFL PD center.
Then, GRX is flashed, so I ran the script (search_FRX_alignment.py) to find the better alignment of PR3, ITMX, and ETMX.

2. Alignment of PR2:

After alignment of GRX, I tweeked PR2 alignment so that IR reflection from ITMX hit on the REFL PD.
Then, IRX flash can be seen.
After the alignment, PR2 OpLev is cmpletely out of range, so we need PR2 OpLev centering to remember the good PR2 alignment.

3. Lock trial of GRX:

I requested ALS_LOCKED state toXARM guardian and GRX can be locked with TEM00 without any problem.

4. Lock trial of IRX:

I rotated IFO REFL HWP from 176 to 146 degrees to increase the laser power on REFL PD.
Then, I requested IR_LOCKED state to XARM guardian.
Though IR seems resonating, IMC trans power oscilated a lot due to the oscillation of MCL control.
The reason of the oscillation is gain change of MCE actuator, so I added a gain of 0.3 in FM1 (3,500) of LSc:MCL filter bank.
After this modification, IRX can be locked with TEM00 without any problems.

I checked PRM MISALIGNED_BF state, which is used for hitting the PRM reflection beam to the HPBD.
Figure 1 shows the state of PRM and thermometers on HPBD.
T cursor shows the time when PRM reached MISALIGNED for BF state.
After that, HPBD temperature increased gradually, which means the reflection beam hit the HPBD.

I offloaded all GAS filters and IP with the FR.

[Yokozawa, Yuzu]

We performed the TCam photo session at 8:06~8:16 this morning. This time, we took only the ITMX image in the Xarm single bounce.

• ITMX Tcam image: [4/1] --> [4/26]
  • horizontal shift = -13.2 pixel = -2.2 mm, vertical shift = +6 pixel = 1.0 mm
  • The position of oplev light also shifted at the same time. We guessed the steering mirror in the chamber might have tilted, due to the vacuum evacuation(klog#29307)? I will check the ammount of the shift is consistent or not later

Date: 2024/4/26 early morning.

I made the states around "SAFE" of Pcal guardian to be safer.

What I did:

• At "TOSAFE" state:
  • The target value of OFS offset values were changed from 0V to 0.01V because the spec sheet of the AOM driver says it should be 0-1 V and I don't know whether a negative value can make trouble.
  • Added a block to cut the injection signal. (This is not an essential feature, but makes it safer)
  • Added a block to close shutters and open the OFS loops. (This is not an essential feature, but makes it safer)
• At "FAULT" state:
  • Added a block to open the OFS loops.
• Adding decorator
  • Made a "shutter_check" decorator to monitor the shutters, and this decorator was adapt in SAFE and DOWN states. Because of this modification, if you opened the shutter(s) at SAFE or DOWN state, the guardian would detect it and kick to TOSAFE state to close the shutter(s).

Hirata, Akutsu; following 29308 and 29312.

Summary

Confirmed the locations of PR2 HR mid baffle and PRM AR and HR mid baffles. Reinforced STM2. Confirmed that the reflected beam from IMMT2 was far from high power beam dump. Confirmed that the beam from PRM was passing far from PR3 (so the open angle of PRM-PR2-PR3 beam seems 0.02 rad).

Setup

• IMMT1 and 2: ALIGNED state; IMMT2 sometimes went to ALIGNING.
• PRM ALIGNED state; depending on the situation, PAY_FLOAT was called; sometimes, wishing rigorously fix the angle of the mirror, LOCK_ACQUISITION was called.
• PR2: mainly PAY_FLOAT
• IO Guardian: PROVIDING_STABLE_LIGHT, and also HOLD_ALIGNMENT to IMC Guardian additionally.

PR2 HR mid baffle

As was confirmed in 29312, we started with checking the beam position at PR2 HR mid baffle aperture, and seemed the spot was 3.5 mm in plus Y direction with respect to the aperture (Fig. 1), as already reported.

PRM mid baffles

It is difficult to confirm the relative postion of the beam spot at PRM mid baffles due to severe accessibility. We tried several ways (see Fig. 2 and 3, for example; they are respectively of PRM AR and HR side; taken by Miyakawa camera on a tripod; maybe due perspetive, it would be hard to say how much the aperture is dislocated with this way). In the end, using the same method as reported in 29282, we were able to "draw" a vertical line to show the center of PRM AR mid baffle aperture. Then inserting a sensor card with a ruler, we maybe able to say that the beam spot would be ~ 5 mm off-centered in the minus Y direction from this line (Fig. 4), while the noimal number should be 6 mm (JGW-T2214066-v1). So we satisfied at this point.

By the way, Fig. 5 is the beam spot on PRM AR target, while Fig. 6 for PRM HR target. As seen, on PRM AR target, the beam spot was mostly centered; on PRM HR target, maybe due to the refraction, the beam spot was a few mm (2.5 mm? see JGW-D2012020-v2) off-centered in the plus Y direction.

At the same time, ghost beams from PRM on PRM AR mid baffle were checked (Fig. 7). The nominal locations are found in JGW-T2214066-v1, and qualitatively no inconsistency. Also, Fig. 8 was taken from IFI-IMM by Miyakawa IR camera; as seen, "both" side of the aperture edge of PRM AR mid baffle seemed equally shining. The small beam spot left of the main beam spot on PRM would be of surface scatter due to the ghost beam (main incindent -> PRM HR -> -refleceted to AR -> reflected to HR -> exit from AR). When this photo was taken, the camera was set in between the optical beams of IMMT1-to-IMMT2 and IMMT2-to-PRM somehow. The camera hight was somehow set at about the same as those beams. The perspective view seemingly be similar to those in 3D CAD somehow, but it would be difficult to say something definit. At least, qualitatively no inconsistency tendency as follows found; the beam spot on PRM seems left-ward; in the AR baffle aperture, the HR baffle apperture edge could be seen like a crescent...

By the way, in Fig. 8, on the IMMT1 shield, three or four apparent ghost beam spots are seemingly distributed, other than the IMMT1 spot itself. In my observation they are all due to PRM main reflection; When PRM Guadian was at PAY_FLOAT, they were dancing, and stopped when ALIGNED or LOCK_ACQUISITION. My estimation senario is that the PRM backward beam is reflected within IFI, which is made of several optics, and each ghost beam would be reached the IMMT1 shield somehow. One can also see a ghost beam spot in the beam dump in front of IMMT1; this SiC one catches a ghost beam from IFI.

STM2 reinforcement

We set another clamp for the pedestal of STM2 (Figs. 9 and 10; the CL-5 type aluminum one in the deeper inside on the table)while carefully looking at IMMT1T QPDs and POP_FORWARD QPDs; this is related to 24703 (ref: 24697 as well, althogh the main topic of this post was not this bump, but some characteristic was mentioned here). Before and after this work, I checked K1:IMC-IMMT1_TRANS_QPDA2_DC_PIT_DQ spectra, but basically no change around 120-130 Hz area; there was a bump (Fig. 11; blue and green are some reference; red is under experiment; the bump slightly shifted after my works/experiments). What I found was that when I only slightly touch a thick cable for picomotors for STM2, this spectum sensitively responded (it was hard to distingush the response whether I would mere shut the optical beam occasionally by my body or not, though...). I checked if this bump would disappear or not by tentatively fixing this cable with white tapes somehow, but not big changes observed. Anyway, the sensitivity seemingly larger than the other point in the IFI chamber I guess.

Please do some cross-check, and hopefully some treatment should be done before closing this area. Currently, maybe most of the frequency band is dominated by acoustic disturbance, so the next time you should make a tube to connect IFI and IMM chambers to avoid this disturbance.

Light beam position near high power beam dump

As already reported in 29308, The light beam reflected at IMMT2 was passing through far off high power beam dump so no clip should happen (Fig. 12).

Light beam position near PR3

The light beam thourgh PRM was passing through far off PR3's recoil mass (Fig. 13). From this, the open angle of the light beams connecting PRM-PR2-PR3 should be not 0.013 rad, but should be close to the nominal designed value, 0.02 rad; PR2-PR3 distance is about 11 m (see wiki), so 0.02 rad open angle means the beam separation must be 0.02*11 = 220 mm or so, which would be consistent with this photo somehow.

Note

A strange thing; according to JGW-T2214066-v1, the PRM AR and HR mid baffle should be displaced about 9.3 mm nominally; the HR one should be shifted in the minus Y direction. But today we found that there was only ~3 mm displacement. Where 6 mm gap went..? Is Fig. 3 (the center of the target seemd offcententered to the aperture, but I cannot discard this is due to perspective or parallax) related to this issue? Actually the beam spot on this target is a few mm in the plus Y direction according to Fig. 6, but may not be 6 mm. At any rate, 6 mm shifting would be too much. That's why we did not touch both sides of PRM mid baffles.

Ushiba, Hirata, Akutsu

Summary

Reduction of LO for PMC locking, which might be similar but not identical (?) found in the past (19472), happened. This LO power was manually (kind of) recovered, but I have no idea how we could avoid this happening again.

Details

During works 29334, IMC or even PMC suddenly became unable to be locked. In my view, this happened when I requested PROVIDING_STABLE_LIGHT to IO Guadian from PSL_LOCKED. Anyway, Ushiba-kun pointed out that LO level was under the threshold (maybe set at 19472). We were not sure what the "LO monitor" channel meant, but I found that the LO signal generator in the PSL room displayed 8.1 dBm while its nominal power should be 8.6 dBm according to a label attached on its body. I tweaked a knob on the signal generator to tweak the displayed output power to 8.6 dBm, but Ushiba-kun said that the "LO monitor" signal was still slightly under the threshold, so I tweaked it to 8.7 dBm, then PSL and IMC lock came back.

I have no idea why and how this happened. Looking at the "LO monitor" to the past, actually recently sudden reduction of the output power were sometimes observed. So this might repeat again.

One hint might be that I saw a kind of "unstable" state changing in IO Guadtian when I requested PSL_LOCKED when I finished works before lunch (but aruond 13:30). What I did before this was just requesting PROVIDING_STABLE_LIGHT to IO Guardian, and then requested HOLD_ALIGNMENT.