I offloaded the following GAS filters with the FRs.

• ITMX: F0 GAS
• ITMY: F0 and BF GAS
• ETMX: F0 and BF GAS
• ETMY: F0, F1, F3, and BF GAS

[Tanaka, Ushiba, Komori]

Abstract:

We started investigating a mysterious coupling between the IR flashing and the green PDH signals.
Our initial tests suggest that the coupling is likely mediated through the RF signals of the IR RFPDs.

Detail:

The issue of the mysterious IR–GR coupling has persisted for a long time.
Due to this issue, we cannot open the shutter in front of the REFL QPDs or increase the power at the out-of-loop CARM PD, and we frequently suffer from lock losses during the IR handover stage.
If this issue can be resolved, a significant improvement in several operational aspects is expected.

To investigate the origin of this issue, we compared the power spectrum of the ALS DARM signal under several configurations, as shown in the figure.
The reference spectra are the blue and green lines, where the PRM is misaligned and aligned after the IR finds resonance with the conventional cable connections, respectively.
IR flashing clearly produced a noisy DARM spectrum, consistent with the noisy behavior observed in the time-series data.

First, we turned off all REFL PDs by switching off the PD power supply board, and we did not observe the additional noise (brown).
Next, we focused on one of the problematic PDs, REFL PDA3, with the PD power supplies for PDA1 and PDA2 turned off and only PDA3 powered on, while the RF output signal was terminated (magenta).
We did not observe additional noise in either case.
This result suggests that the issue is not caused by a simple cable connection without the power supply, but rather by the connection between an operating PD and the demodulator.

Next, we measured the noise with PDA3 connected using a different cable instead of the conventional one.
In this case, the noise reappeared (green), indicating that the issue does not depend on the cable routing.

Tomorrow, we will test the effect of inserting an RF transformer (T1CA made by R&K), which isolates the ground and blocks the DC signal between the input and the output.

[Takahashi, Washimi, Hirata]

We did preparation for installation of SRM IRM dampers.Today, we locked suspension, and Breadboard. After that we removed Mid-size baffles from the breadboard.

1. Lock IP and Topfilter
After opening the top flange of chamber, we locked IP and Topfilter. We covered suspension by Seiden-sheet. (Guardian status was already SAFE mode.)

2. Check the mirror height
We checked the mirror height by laser leveler. Beam height is indicated on SRM chamber(Main mark is on +Y+X side. Copy is on -Y+X side. pic1, pic2 )
Unfortunately, Beam height is close to the edge of side flange. So laser leveler could only be used near the center.(pic3) We put green laser leveler at the +X side, and align to the Beam height mark on the chamber.
And put red laser leveler at -X side, and align it to the +X side green laser leveler(pic4). Recoilmass front ring has center mark. We can see the laser leveler height and the recoilmass center line.

・+X side (Green line) looks same as recoilmass center line.(pic5)
・-X side (Red line) looks 3 millimeters away from the recoilmass.(pic6)

3. Check the Bread board height
Laser leveler can only used around center of side flanges. So we can only check the height near the center.

・+X side (Green line) is 380.5mm.(pic7)
・-X side (Red line) is 383.0mm.(pic8)

4. Lock the Breadboard
Turn 4 foot screws to lower  that until they touch the block. After that, added 4 masses(Total 20kg) on the breadboard for locking. (pic9)

5. Lock the Suspention
Bottomfilter, IMR, IM, RM and TM were locked.

6. Mark the Mid-size baffle position
To record the current baffle positions, 3 blocks(AL clamps) were set on each baffle.(pic10)

7. Remove Mid-size baffles
We removed 4 fixed clamps, and removed mid-size baffles(AR side and HR side). Clamps for the mid-size baflles remain on the bread board.(Note that those positions have been changed.) (pic11)
Removed Mid-size baffles are on the tables have 4 pillars, and wrapped by plastic films. 4 pillars preventing plastic film touch baffles. (pic12)

*We weighed removed baffles.

・HR side : 4.94kg
・AR side : 4.931kg

Today's pictures are https://www.dropbox.com/scl/fo/1dw0adstbz35z85i0vd91/AJlOguQbuxD332fX1ZaIiYE?rlkey=xv1ztcd0wli70ukd0hxlslcl0&st=sfhiadap&dl=0

Ushiba, Komori, Tanaka

We tempolary replaced the LO to the other one, which was used PLL before (fig.1). Now, GRX could be locked.

Ushiba, Yokozawa, Tanaka

This morning, we found that GRX could not be locked even though the flash amount seemed to be large enough (> 0.8 from the view of K1:LSC-TR_GRX_NORM_OUT_DQ ). According to the GRX PDH error signal channel (K1:ALS-X_PDH_MIXER_DAQ_OUT),  Any PDH-like signals seem to be not observed. However, since the DC power on the PD has some responce whenever GRX was flashed, the PD for PDH itself seems to be turned on. Also, CMS seems to be turned on because K1:ALS-X_PDH_MIXER_DAQ_OUT has some responses when we operated some switches on the CMS. So we suspected that the LO has something wrong.

Yokozawa-san and I entered mine and confirmed the LO and the CMS for PDH were turned on. Then, we checked whether the LO emitted the 33 MHz signal or not by using Moku:lab. However, we could not obsered any signal at 33 MHz. (This time, we confimed Moku:lab could be observed the output of GRY LO which emited the signal with the almost same amplitude at different frequencies.)

We tried to solve it by restarting the LO but the situation was not changed. After this, we found that the "UNLOCK" and "ERR" sign were shown on the display. we checked the error messages. There are many error messages (fig.1).

According to the manual, we need to ask the manufacturer to fix the LO in the case that their messages are shown. This afternoon, we will bring the other RF generator from Mozumi and try to solve this issue by replacing the LO.      

I commented out all the request for SRM in te LSC_LOCK guardian and INITIAL_ALIGNMENT guardian.
These guardians can be used without conflicting SRM hardware work now, so I executed these guardians.

The Check 3 script has been developed and tested.
The comparison between the LL spectrum and the RAW-based reconstructed spectrum shows generally good agreement.

Detailed Working Logs:

• Work log top page
• Working log for the check 3 script: link1, link2

I offloaded the F0 and F1 GAS filters in IX with the FRs.

I offloaded the following GAS filters and IP with the FRs.

• ITMX: F0 GAS
• ITMY: F0 GAS
• ETMY: F0 GAS, H2 IP

[Kimura and Yasui]
 Temperature calibration data was registered to Y-end Cryocon.
The registration date and time were March 6, 2026, 11:00 AM to 11:30 AM.
The name of the Cryocon to which the temperature calibration data was registered is EY2: Duct Shield 1.
The registered temperature calibration data is the resistance/temperature curve for a platinum-cobalt resistance thermometer (PtCO).
After registering this temperature data, the temperature calibration data for channels D to H channels of EY2: Duct Shield 1 were changed from platinum resistance thermometer (Pt100) to PtCO.
The resulting temperature difference at room temperature was +2 K.
This temperature difference increases significantly at cryogenic temperatures.

[Kimura and Yasui]
 From 13:30 to 16:30 on March 6, the SRM was pressurized to 87 kPa with compressed air below the dew point of -40 Celsius degrees.
It will continue to be pressurized to atmospheric pressure on March 9 morning.

Soon after Type-A suspensions are aligned, both GRX and GRY flashes inside the arm cavities.
So, no serious misalignment happens during the blackout.

Though saturation of the actuators occured, all VIS finaly reached the LOCK_ACQUISITION state after offloading actuators.
Since ITMX F0 GAS and ETMY IP H2 actuators are saturating, they should be offloaded again.

I glued the magnets to the side plates for the IRM damper. 

I offloaded the following GAS filters and IPs with the FRs for the recovery from the power outage.

• SRM: F0 GAS, H1 IP
• SR2: F0 GAS
• SR3: F0 GAS
• BS: F0 and F1 GAS
• ITMX: F0, F1, F2, and BF GAS
• ITMY: F0, F1, F2, F3, and BF GAS
• ETMX: F0, F3, and BF GAS
• ETMY: F0, F1, F2, F3, and BF GAS, H1 and H2 IP
• PR3: SF and BF GAS (FR for SF GAS reached SW limit)

The detchar computers (k1det0, k1det1) came back online from the power outage. The regular production of the segment files at k1det1 restarted without issues.

Ushiba, Tanaka

Ushiba-san found that GR beams did not reach the input mirrors even though PR3(SR3) alignment was restored. According to each GR input monitor on POP/POS, GR beams seems to reach to POP/POS table. So I entered the mine and checked the GR laser shutters works or not.

At first, I checked the GRX laser shutter on the POP table. Since the display showed something, the driver itself seemed to be turn on. In this state, I tried to open and close the shutter by medm screen. However, the shutter did not work. Then, I tried to open and close the shutter manually by using the wheel on the driver. I confirmed that I could open and close the shutter manually. So the driver and shutter themselves seems to work. Again, I retried to open and close it by medm screen. Then, I could do so.

Similarly, the GRY shutter could be recovered by the same procedure.

We are not sure of the reason why. One of possibilities is that the current amount to work the shutter is not enough. We used Thorlabs SH1 as the GR shutter and  Thorlabs KSC101 as the GR shutter driver. However, KSC101 is designed for a half inch shutter but SH1 is a 1-inch shutter. So we used the driver to work the larger shutter than one that makers expect. Maybe while the driver keep working, we can move the shutter remotely. However, the driver is turned off once. we may need to move the shutter manually once in order to move it remotely .

I paused LSC_LOCK and INTIAL_ALIGNMENT guardian because they change SRM guardian state and would be dangerous during SRM hardware works.
Please do not use these guardians until properly managed their guardian state not to change SRM state or SRM work will be finished.