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)

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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

>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.

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.

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

[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).

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

[Akutsu, Tamaki, Takano, Ushiba]

First, we checked the viscosity of the liquid yesterday (movie1: sample in the bottle doesn't seem high viscosity. movie2: sample in the bowl seems high viscosity).
Then, we tested if the liquid can be melt in the following things.

1. Water: not melt and liquid is float on the water surface
2. Ethanol: not melt and liquid sank in the ethanol.
3. Aceton: melt easily

We stored all samples in the draft chamber and put labels below each sample.

The speed of melting in the case of acetone is fast or slow or that you need to mix by some bar many times? 

Additional comment: The difference between the one in bottle and the other in bowl was that the bowl one was left (with its upper opened) in the draft chamber (in operation) for a half day (from yesterday's evening to today's morning) so something might evapolate during this period. The bottle was sealed and was out of the draft chamber.

[Ikeda, Takahashi]

We tried to take pictures and movies inside the bottom bellows with the fiber scope. The picture and movie (better quality) show the gap between the pillar and the bellows.

[Kimura and M. Takahashi]

 To identify the source of the liquid material that entered the EYA tank, three filters of the air compressor and the inside of the connection piping of the dry pumps for vacuum pumping were visually inspected.
As a result of the visual inspection, no traces of liquid material were found inside the filters of the air compressor and the connecting piping of the dry pumps for vacuum pumping.
The smell inside the filter and piping was confirmed by nose, but the same irritating smell observed in the EYA tank was not found.
Three filters of the air compressor were replaced with new ones because more than two years had passed since the last replacement.

1. Results of Q-mass measurements
　Q-mass measurements of EYC were performed on June 24 and June 25.
The mass detection range is m=2 to m=100.
The displayed values in the attached graphs (Graph 1 ~ 4) refer to two types of total pressure and sensitivity calibration values.
Both graphs show that many partial pressures are distributed between m=16 and m=18.
Since the values are close to the cracking pattern ratios for H2O(m=18) shown below, it is presumed that most partial pressures between m=16 and m=18 are derived from H2O.
Total pressure: 5.44 x 10^-4 Pa
H2O(m=18): 100 % <- 4.1 x10^-4 Pa (100 %)
OH+(m=17): 25 % <- 9.4 x10^-5 Pa (23 %)
O+(m=16): 2 % <- 9.4 x10^-5 Pa (1.4 %)
　The reason for the high EYC pressure is thought to be the result of water deposited on the inner surface of the duct during cleaning inside the EYA and between the EYA and EYC, which continues to be released as outgassing.
　For reference, the partial pressure ratios from m=16 to m=18 before duct shield cooling in December 2022 are shown.
Total pressure: 4.19 x 10^-5 Pa
H2O (m=18): 100 % <- 2.38 x10^-5 Pa (100 %)
OH+(m=17): 25 % <- 5.39 x10^-6 Pa (23 %)
O+(m=16): 2 % <- 4.3 x10^-7 Pa (1.8 %)

2. Vacuum leak estimation
Examine whether a vacuum leak is occurring at EYC.
If the ratio of O2(m=32) to N2(m=28) is 1:4, a vacuum leak may be present.
From the measurement results, the ratio of O2(m=32) to N2(m=28) is
O2(m=32):N2(m=28)=1.19 x10^-6 Pa:3.65x10^-6 Pa=1:3.
In addition, Ar (m=40), which is present in the atmosphere at about 1 %, has a partial pressure (1.25x10^-7 Pa) relative to the total pressure (5.44x10^-4 Pa) in the Q-mass results, which is 0.023 %< 1 %. 
 Based on these results, it is presumed that there is no significant vacuum leakage, but a leak test is necessary to make a final determination.
 
3. About CO2
 CO2 is  estimated to be generated by desorption from the inner surface of a vacuum vessel that is not baking like KAGRA.

Results of Q-mass measurements
　Q-mass measurements of EYC were performed on July 19 and July 21.
The mass detection range is m=2 to m=100.
The displayed values in the attached graphs (Graph 1 ~4) refer to two types of total pressure and sensitivity calibration values.
Both graphs show that many partial pressures are distributed between m=16 and m=18.
 
On July 19: 
 Total pressure: 1.21 x 10^-4 Pa
 H2O(m=18):  7.0 x10^-5 Pa
 N2 (m=28): 1.2 x 10^-5 Pa
 O2 (m=32): 2.3 x 10^-6 Pa
On July 21: 
 Total pressure: 1.76 x 10^-4 Pa
 H2O(m=18):  5.1 x10^-5 Pa
 N2 (m=28): 2.1 x 10^-5 Pa
 O2 (m=32): 4.8 x 10^-6 Pa
The pressure in the EYC maintains a decreasing trend. The main component of the residual gas is H2O.
The higher pressure on July 21 than that on July 19 is due to the vacuum leak test conducted from July 19 to July 20.

Results of Q-mass measurements
　Q-mass measurements of EYC were performed on July 25 and July 30.
The mass detection range is m=2 to m=100.
The displayed values in the attached graphs (Graph 1 ~4) refer to two types of total pressure and sensitivity calibration values.
Both graphs show that many partial pressures are distributed between m=16 and m=18.
 
On July 25: 
 Total pressure: 8.05 x 10^-5 Pa
 H2O(m=18):  5.3 x10^-5 Pa
 N2 (m=28): 2.3 x 10^-6 Pa
 O2 (m=32): 4.0 x 10^-7 Pa
On July 30: 
 Total pressure: 7.24 x 10^-5 Pa
 H2O(m=18):  4.2 x10^-5 Pa
 N2 (m=28): 1.8 x 10^-6 Pa
 O2 (m=32): 4.2 x 10^-7 Pa