[Yokozawa, Yuzurihara]

We performed the lockloss investigation for the recent lockloss of 2025-07-10 10:53:19.187500 UTC. The previous lockloss investigation was posted in klog34259. This is the longest lock in the O4c by now.

Quick summary 

Although I check all the lockloss phenomena which were reported in the past klog, those phenomena except for the OMC DCPD saturation did not occur just before this lock loss.
The OMC saturation occurred just before the lockloss. But, the quickness of the saturation seems to be different from the past saturations. I and Yokozawa-san checked the timeseires and listed up the possible cause of the saturation. 

Details

• There was no excess on seismic motion of 1~10 Hz. (Figure 1)
• About the oscillation, we can see the oscillation on the PR2 pitch with 0.83 Hz. But, the amplitude is not large. (Figure2)
  • We can see the coincident oscillation (0.83 Hz) on the ASC PRC2 pitch and ASC MICH pitch. (Figure3)
• There was small excess on PRM feedback signal. But, it will be small to cause the lockloss. (Figure4)
• About the drift, there was no drift on Xarm and Yarm mirrors over 30 minutes. (Xarm, Yarm)
• About the BPC control, there was no strange behavior just before the lockloss
• About the saturation of control, there was no saturation on BS and ETMX.
• There was no glitch on ETMY MN oplev.
• There was no earthquake around the lockloss time.
  • We can see the large seismic motion in 3~10 Hz and 10~30 Hz. This excess ended 20 minutes later. But, this amplitude is not enough to cause the lockloss. (Figure)

Quick OMC saturation

At this lockloss, we can see the OMC saturation, which we reported many times in the past klog. This will be the direct cause of the lockloss. I and Yokozawa-san checked the original cause of the OMC saturation.
One important difference between this saturation and past saturation is the quickness to reach the saturation. As seen in Figure9 and Figure10, the DCPD signal reached the saturation within 1 ms, which is so quick!
We are thinking it's difficult to make this quick saturation by the suspension. So, we guess it might be associated with the electrical signal or glitch.

In the past saturation, we could see the several oscillation just before reaching the saturation as shown in Figure 11 or this. This might be a hint to investigate the cause more.
Anyway, this was new phenomenon for us (or I missed this phenomenon...).

Other findings

• The volage monitor channel
  • While K1:PEM-VOLD_OMC_RACK_DC_M18_OUT_DQ is stable, K1:PEM-VOLD_OMC_RACK_DC_P18_OUT_DQ shows the drift behavior and it reset somehow. (Figure 12)
  • K1:PEM-VOLT_AS_TABLE_GND_OUT_DQ is almost stable but shows the unstable behavior at -5 hour and just before the lockloss.
  • It's highly important to check the ground condition around AS port and OMC rack.
• PMC control
  • K1:PSL-PMC_LO_POWER_MON_OUT16 shows some jumps before the lockloss. It would be very helpful if the PMC expert could comment on this phenomenon.

Date: 2025/7/11

I performed this work as a weekly work.

Attached figure is a screen-shot just after the work.

[KImura and M. Takahashi]

 At around 10:20 a.m. on July 11, during a routine patrol of Y-end, the occurrence of a strange noise was confirmed near Y-27.
The source of the noise was the cooling water unit for the TMP of the Y-27 vacuum pump, and the cause was a lack of cooling water.
Therefore, the GV of the Y-27 vacuum pump was closed and the TMP was stopped.

 At approximately 1:40 p.m., the cooling water unit was refilled with water to put back into service the Y-27 vacuum pump, and the unit was put back into operation.
As a result of the operation, there were no problems with the TMP or the cooling water unit, and the unit was in regular operation.
As a precaution, we decided to leave the repair equipment at Y-27 and check the situation during the next scheduled patrol.

[Kimura and H.Sawada]

 Two turbomolecular pumps were delivered.
These turbo molecular pumps were transferred to the front room of the parking lot and are temporarily stored next to the lift truck.

[Nakagaki-san, Ikeda]

Summary:
This work is related to K-Log#34519: Offload of F1 GAS.

Due to a communication failure with the network switch located in the SRM VIS mini-rack, communication with the SRM GAS Stepper Motor was lost.
To recover, we restarted the SRM network switch by unplugging and reconnecting the LAN cable on the OMC side, which supplies PoE to the switch.

Details:
We received a report from R. Takahashi-san that the SRM GAS Stepper Motor was not functioning.

Upon investigation, we found the following:

The relay of the Stepper Motor showed slight response.
There was no ping response from k1script1 to the LAN-serial converter.
The SRM VIS mini-rack network switch did respond to pings from k1script1.
However, the web interface of the network switch was unresponsive.
Based on this, we suspected a communication failure within the SRM network switch.

Since the SRM network switch uses PoE, its power can be controlled from the OMC side. However, we were unable to locate the port list for remote control.

Therefore, after consulting in the control room, we decided to enter the tunnel for manual intervention.

14:13 - Entered the center and reconnected the LAN cable from the OMC network switch to the SRM.
14:15 - Confirmed at the BS area workstation that the SRM GAS Stepper Motor could be turned ON via BIO and scripts.
14:18 - Handed over control to Takahashi-san.
14:19 - Exited the central area.

OMC Network Switch Port Assignments:
Pico Network
01: PD mini rack switch  
02: OMC mini rack switch  
03: SR3 mini rack switch  
04: SR2 mini rack switch  
05: SRM mini rack switch  
06: BS mini rack switch  
07: PR2 mini rack switch  
08: Green X Table switch  
09: Green Y Table switch  
10: AS Table switch  
11: Precision Air Processor SRX1
12: AS_WFS HWP  
DGS Network
18: OMC Workstation  
 

[Kimura, M.Takahashi, H.Sawada and Yamaguchi]

 We transported the experimental equipments at the parking lot in the mine to inside the prefab house at the Kohguci.

The equipments will be temporarily stored in the prefab house until July 15.

I accepted the following differences of SDFs (see related klog34517, klog34518, and klog34519). SDF #25-27 were reverted because of misoperation.

[Takahashi, Ikeda]

I offloaded the F1 GAS with the FR. The stepper motor initially did not work due to a network switch problem, which was recovered at the site by Ikeda-san.

I offloaded the SF GAS with the FR, which reached the maximum limit (1360000 steps).

I offloaded the F0 GAS with the FR.

I took the TCam photos for four mirrors at 9:30 ~ 9:37 this morning. The previous work is klog34453.

• ETMY
  • original
  • fitting result
  • previous reference
• For these mirrors, I updated the reference positions. I also re-draw the yellow line shown at the k1mon4. For the other mirrors, we don't need to update the reference positions.

A CAL Tcam session was performed to obtain beam position information necessary for Pcal. The parameters have already been updated, and SDF is expected to be accepted.

Operator: Dan Chen, Shingo Hido

Update Time: 2025/07/11 09:16:29

Update Time: 2025/07/11 09:17:49

Update Time: 2025/07/11 09:18:10

Update Time: 2025/07/11 09:18:46

After this long lock, the BNS range seems to be sometimes degraded during locking. It is better to check the IFO conditions, especially those related to ASC and/or signal saturation. Some excess noise was visible around 60 Hz to 100 Hz.

Because of a small number of earthquakes, over 18 hours of continuous locking was realized.

However, the lock loss seemed not to be related to seismic noise shock.

I measured the coherence between DARM and IMC ASC signals with 128 average during the stable run today (fig1).
Some large coherence can be seen in IMC WFS signals and DARM.
To evaluate the noise comes from beam jitter, noise projection with IMC WFS might be helpful.

As reported in klog34442, there is a coincidence between glitches in OMC DC PD and sensitivity degradation.
So, I tried to systematically understand the kick of the suspension and sensitivity degradation.

As shown in Fig. 1, when glitches are very large, the OMC DC PD signals can become saturated.
In this case, the calibrated DARM signal is no longer reliable, so it should be excluded from the data analysis.

In other cases, the amplitude of each glitch is different, so I categorized them into four groups based on the maximum signal in each glitch: more than 25,000 counts (#1), between 20,000 and 25,000 counts (#2), between 15,000 and 20,000 counts (#3), and less than 15,000 counts (#4).
Figures 2-5 show the Q-transform around the glitch categorized as #1, #2, #3, and #4, respectively.
Even in category #4, some excess can be seen around 60–90 Hz.
So, it would be nice to evaluate the non-lnear effect in DARM sensitivity.
Figure 6 shows the comparison of the spectra when glitches happened (as a reference, spectrum without glitches are also shown with black lines).