Yamamoto, Tanaka

After today's maintenance work we noticed that the laser output was at zero. We checked how long it had been zero and found that the laser output had dropped to zero all at once at around 10:50 today. According to Yamamoto-san, this was before the maintenance work had been carried out.

Later, when we looked at the laser controller screen via the webcam in the PSL, we saw the error message "temperature too High, Master Fault" (Fig, 1) The temperature displayed on the controller was 52°C, which was much higher than the nominal value of 23°C.

When we entered the mine, we first checked whether the chiller was working properly, and the chiller temperature display showed a nominal value of 19 degrees Celsius, which seemed to be working properly.

We then entered the PSL and touched the enclosure of the fibre amplifier and did not feel any heat in the enclosure. I also held up a sensor card around the laser's output port and found that a very weak light was emitted. The "seed" value on the controller was about 1.4. According to Nakano-san's manual, this "seed" value indicates the incident power to the fibre amplifier and should be between 1.0 and 2.5 as a nominal value. In other words, the incident power is considered to be normal. The current value of the NPRO controller was about 0.96 A, which is the nominal value, so the NPRO controller is probably normal.

According to Nakano-san's manual, in this case it was most likely a thermometer malfunction, which was fixed by switching off the laser, unplugging the connection cable from the amplifier to the PC and restarting the application, so we thought we would try this approach. However, at the beginning of the manual, there is a warning that if the amplifier is switched on while the seed laser is off, it may break down, while the operating procedure states that the power should be switched on from the amplifier. This contradicted the warning, and as we could not decide which was correct, we decided not to power down the whole laser today (although we are sure the warning is correct).

Instead, we first switched off the fibre amplifier only and restarted it. However, the situation remained the same. We then switched off the fibre amplifier, closed the app, and then restarted the amplifier and the app. However, the situation remained the same.

At this point, we noticed that before pressing the "ENABLE" button on the controller app, i.e. when the laser was not emitting, the thermometer on the controller was showing around 3.5°C, and when we pressed the "ENABLE " button was pressed, the value of the thermometer rose up to 52 degrees Celsius drastically. When the "STOP" button was pressed, the thermometer value suddenly dropped from 52°C to about 3.5°C. This seems to be an odd behaviour of the thermometer.

At any rate, as it was late, we finished today's investigation.

Tomorrow, we will try to restart the whole laser system including seed laser.
 

Abstract

Details

[Dan, Hirata, rTakahashi, Tamaki, Ushiba]

We installed three additional cables between BF and PF (B49, B50, and B51).
Then, we replaced Dsub connectors on BF.
Followings are the cable numbers before and after replacement,

Old cables are cut and clamped on the BF.
We will continue the cabling at PF stage tomorrow.

Note:

During the work, we removed radiation shield plates between BF and PF.
They are stored in the cryostt, and need to be reinstalled after finishing the cabling.

[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.