[Kimura, Ushiba, M. Takahashi, Sawada (Hokuto) and Ueda (SK)]

 We had closing flange work for IYC on Apr. 15, and closed two cross tube flaneges and one K-800 side flange of IYC.

During this work, we found a white label that has been left in this EYA chamber maybe for 6 years... and detached it.

After the mitiigaing work, We tried to switch the IMC CMS IN1GAIN between 15dB and 16dB with IMC locking. Thanks to the mitigaition, IMC could keep the lock with the swithing (Fig.1). It means that we can increase the input power without any trouble. 

[Akutsu, Ushiba]

We investigated EYA chamber and obtained a sample of the liquid inside the chamber.
We used sysringe with tubes to obtain a sample and stored in the plastic bottole for ethanol.
We also obtained a small amount of the liquid in the stainless bowl.

The  sample volume is about 50 ml and the color of the sample liquid is yellowish (fig1).
Also, I felt the liwuidd is thick during gathering the liquid with syringe.

We stored stainless bowl in the draft chamber to check if the liwuid will be evapolated (fig2, fig3).
We also stored a bottle of the sample at the clean booth of draft chamber (fig4).

[Hirata, Ikeda-san]

We apply First contact to PR2 mirror. We will pill off them tomorrow morning.

１．Lock Suspension（IM→RM→TM）

２．Cleaning（floor, inside chamber by vectra-α with ethanol and vacuum cleaner）

３．Surface inspection of HR and AR side by photo

４．Set FC jig

５．FC apply(AR→HR)

Before appling FC, we saw some edge and footprint of FC on HR and AR side. Those are 500mm or 600mm away from the center.
And also we saw some dots and small dust near the center. We will check it tomorrow morning after pill off FC.

Photo shooting was very difficult like PRM.(Especially AR side) 

I uploaded today's photo to KAGRA dropbox.

I checked OpLev beam path during the installation of SI at IYC.
I confirmed all OpLevs were not clpped by SI.

Since I haven't centered MN OpLevs, OpLev centering should be done before starting pumping.

So, please do not start pumping around IYC area until centering OpLevs of IYC.

For your information. My EYA NAB check on Mar 28, 2024 -> 28997

And the attached photos are additional photos from my directory on that day

Since the earthquake, the pressure at X-27 has tended to increase.
See attached graph.
Periodic inspection records (in Japanese) show no pressure change in X-15~GVmtix.
Inspection-records
Since the pressure increase started immediately after the earthquake, a leak is suspected.
From the estimation, if it is a leak, it is estimated to be 2.8 x 10^-10 Pam^3/s.
Consider leak inspection of X-arms.

This warning seems to vanish around 1:33 according to the records. Anyway, we need more investigation.

Around 0:00, the low water level warning in x was reported via the KAGRA warning system. The warning level itself is regarded as light. I have already reported this situation to Hayakawa kun and several sad members for the next day checks.

Actually, the indicators for x and corner warter suppliers for the cruocoolers showed some warnings. However all water cooling type coolers such as precision coolers and daikin coolers were working.

One more important investigation was pointed out by Uchiyama-kun at the Friday meeting. That is whether the liquid exists in the cone below or not. We need a flexible fiber scope or some simple inspection tools to check the liquid in the cone below. If it is, the cleaning work can be the reconstruction of the stuff around EYA. Some members are proposing a method to avoid this reconstruction to save time.

>The first report some pollution on Tcam mirror in the EYA tank was in February. https://klog.icrr.u-tokyo.ac.jp/osl/?r=28644

This is just a comment. The dust on the TCam mirror in the EYA tank was cleaned on Friday (klog#29213). The mirror could have been cleaned without a complicated cleaning procedure. So, it seems the dirt on the TCam mirror is caused by something other than the oil-ish liquid in the EYA chamber.

Some members in the KAGRA-PMS mailing lists were called to join the discussion on this topics and discussed where it came from, what is this material, and what should we do for this issue at 23:00 on last Friday.

Anyway, we need more investigation on, such as what is the process, sampling, material identification (in the commercial company), the strategy on how to remove this material, and how to clean it. Kimura-san will check whether he can safely open and close the IFC70 flange at the bottom of this type of vacuum tank on Monday. If possible, we can remove at least the liquid. The cleaning method depends on this liquid material. Uchiyama-kun will also try to reopen the closed IYA tank to check inside. About EXA, the vacuum level is not bad during pumping. So no such material is expected because it should be much worse if it exists.

I just guess the total cleaning of this EYA tank will take ~ one month or so. (Just my guess)

---

The first report some pollution on Tcam mirror in the EYA tank was in February. https://klog.icrr.u-tokyo.ac.jp/osl/?r=28644

I checked the dark noise of TRANS and REFL and found it to be dominant above 1 kHz and 10 Hz, respectively, as shown in the attached figure.
Therefore, the second and third puzzling points can be explained.

It seems a bit strange that the dark noise is larger than the measured noise with light at the REFL PD.
This can be explained by the fact that the dark noise of some PDs is better with light than without light.

A potential solution to the first puzzling point is that this intensity noise comes from residual length or frequency fluctuation, rather than the intensity noise of light.
We might be able to improve this by adjusting the offset of IMC LSC.

I can garantee up to +/-20 deg roll of the OSEM flag (see this paper), but 40 deg roll might not be within the garanteed range...

[Hirata, Ikeda-san]

We apply FC to PR3 again.

• Drying time: 4h(center part), 2.5h(tag part)
• Applyed 2layers. After appling first layer, we waited 15min. And applied 2nd layer.
• AR side: We can see tag footprint(about 700mm away from the center) and some small dots.
• HR side: We can see upper edge(about 800mm away from the center) and small dots near the center.

I uploaded pictures to KAGRA Dropbox.

[Hirata, Ikeda-san]

I pilled off FC on PRM mirror. Some edges remained.

• Drying time: 22h 
• AR side: We can see tag footprint and edges(about 30mm away from the center).
• HR side: We can see upper edges(about 60mm away from the center).

I uploaded pictures KAGRA Dropbox.

With Uchiyama, Yokozawa, Yuzu, Takase

We found a pool of liquid the bottom of the EXA like a lake.
The size of the lake was difficult to estimate, but the order is about 1cm in depth and 20cm in diameter.

• Liquid-like material was seen on the optical table surface, on the Pcal mirrors, and on the H steel.
• Also there are small drips in the vacuum tube between EYA and EYC.
• We used a black light to check them, and they looked slightly blue or green.
• We used a long band and a Kimwipe to get a little of the liquid. To the touch, it was viscous and oily.
• There was no liquid on the NAB, but there were traces of what appeared to have dried up.

Picture: link

[Tomura, Kamiizumi, YamaT]
 

Abstract

We updated the IMC model to mitigate glitches coming from a timing gap of the BO operation, which makes a lockloss related to IMC and/or CARM controls.
Now, changing gain on MC common mode servo can be done more smoothly same as the test on the standalone system.
Because we cannot output laser today due to another works, we haven't tested this code with locked IMC yet.
 

Details

When we faced locklosses related to the gain change of IMC servo first time, we doubted the difference on the offset between 16dB and 15dB as a cause of lockloss (see also klog#26657). But we found larger change in offset during a gain change than the offset difference between 16dB and 15dB by some tests on the standalone system as discussed in the thread of klog#29112. Changing gain especially for 16dB->15dB and 8dB -> 7dB by BO makes glitches because delay of photocoupler is different between ON and OFF. BO supported by LIGO RCG has an asymmetric delay as 200us (maximum). So, when we change a gain from 16dB (0b10000) to 15dB (0b01111), the actual change is 16dB (0b10000) -> 31dB (0b11111) -> 15dB (0b01111) within 200us as shown in Fig.1. Finally, we could mitigate this glitch by preparing a new real-time model to mitigate the timing gap of BO on the standalone system.

Because the new real-time model seemed to work fine on the standalone system, we installed it in the IMC model. By mitigating a timing gap of BO operation, a change in an offset voltage at OUT2 is also mitigated from Fig.1 to Fig.2 (Fig.1 was taken in last week because I forgot to save it today...). In the new real-time model, ON and OFF on BO operation can be done almost simultaneously. So we can change a gain from 16dB to 15dB not via 31dB. A situation in the case of 8dB -> 7dB is also improved from Fig.3 to Fig.4.

Latch and intentional delay can be controlled on the MEDM screen (see above IN1GAIN controller in Fig.5). Please keep "ON" for "Use Latch" button if you want to use latch function. When it's in "OFF", latch function is disabled. About a sample number of delay, we confirmed it worked well in N=0~2. Latch channel and gain channel are output from another BO cards each other because of the pin assignment. So this delay is prepared to compensate an individual difference of two BO cards if it's too large. When we will install this model also for CARM common mode servo, we must confirm same things.