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LAS (bKAGRA laser)
shinji.miyoki - 21:19 Monday 25 November 2024 (31757) Print this report
Water leak from a Beam Dumper for the IMC REFL

[miyoki, ushiba, tanaka, uchiyama, hayakawa, takahashi, sawada, ohmae]

Abstract

The water leak of the beam dumper for the IMC refl happened and water spread on the optical table. After wiping water, we removed this beam dumper and connected the two tubes for this beam dumper. At present, two beam dumpers for the shutter and PMC refl are operated by a water chiller.

What happened

  1. Accident COnfirmation
    1. The commissioners started suffering from the PMC/IMC alignment changes before ~ 12:00. They tried to recover the alignment by changing many parameters.
    2. Finally, the laser downed. (~12:20)
    3. Ushiba-kun and Tanaka-kun checked the water chiller for the beam dumpers and found that there was no water inside. (photo.1)
    4. After turning on the light inside the PSL room, I found that water was on the optical table around the beam dumper for the IMC refl via webcam. (photo2) (If you enlarge the photo, you can notice the edge of the yellow tube was situated at the edge of the transparent sleeve. This meant that this yellow tube was disconnected, and the water leaked from this position.)
    5. Consequently, the water spread around the input optics for IMC (photo3, photo4), and floors around -Y side of the optical table (photo.6). Judging from the photo5, the water that entered the M6 holes around the water leaking point seemed to drop at the bottom corner of the optical table at +X- side.
    6. (note) The reason why for the phenomena in (1) could be the change of alignment of optics on the table due to the deformation of the optical table covered with cooler water.
  2. Optical table and beam dumper Recovery
    1. We changed the PSL mode to working mode. (Open doors and operate both precision coolers, and operate KAOCH filters)
    2. I stopped the chiller for beam dumpers, and we started to wiped water on the table by using bencotton not to hit mirrors and drop water on mirrors. On the other hand, a vacuum cleaner was used to absorb the water on floors. 
    3. When I touched the yellow side tube, it easily detached from the tube connector. So we concluded that this was the water leaking point. 
    4. I removed the other tube for this beam dumper and checked whether there was stuck or not inside this beam dumper by injecting air by an air duster. However, the air could pass through the beam dumper! So there seemed to be no stuck when I checked. (I don't know what happened when the water leaking started)
    5. I also injected air toward the two beam dumpers, then we confirmed that the air could pass through to the chiller position. Also I checked the other pass to the chiller. Also I confirmed that the air could flow to the chiller. So we concluded that there was no stuck in the water path for the two beam dumpers (for PMC refl and shutter)
    6. Anyway, I decided not to use this beam dumper and connected the yellow tube and white tube directly as in photo7 to close the water pass for the two beam dumpers. The connecting point was set outside of the optical table and set the joint position at the bottom of the bending tube to prohibit the leaking water from drop to the optical table side throgh the outside of the tubes. 
    7. To clean the water pass for the two beam dumpers, we kept filling fresh tap water from the chiller and abandoned the returning water to the chiller. Actually, the water showed white color with some material. After the returning water seemed to be transparent, we recovered the closed water loop for the chiller to circulate water to two beam dumpers. We also confirmed that the temperature for the two beam dumpers reduced after the chiller reoperation.
    8. On the other hand, we used an air cooling-type beam power meter  (max 30W injection) to dump the beam of IMC refl as photo8. A thermometer was also attached to its backside. The recovery of this air-cooling type beam dumper was of course done after restarting the Fiber laser because we should know the precise position of the IMC refl beam.
    9. Before restarting the Fiber laser, we checked the mirror surface condition around the water leaking point, especially on the surface of the IMC input window as photo9/10. We believed that there was no contamination with water. There also seemed no serious pollution with water drips on other mirrors.
  3.  Laser recovery
    1. We restarted the Fiber Laser, then found that the PMC transmittance was low maybe because of the alignment change during the working mode and the optical table deformation by the leaking water. Tanaka-kun and Ushiba-kun readjusted the alignment to the PMC and obtained a reasonable PMC transmittance at ~ 20W power operation.
    2. After that they tried to recover the IMC lock. However, also they encountered the low IMC transmittance because of the alignment changes. Although they tried to recover the alignment to obtain the better transmittance, the present transmittance seemed to be lower than before. Actually, the IMC control also encountered the feedback signal situation maybe due to the air flow/temp changes in the PSL room because the working mode was kept for dying water.
    3. The water on the optical table seemed to dry up. However, we had no way to check the water inside the optical table. Anyway, we will keep working mode for one night for drying.

What caused the tube disconnection?

  • One week ago, we encountered the stuck of water for the beam dumpers. At that time, we recovered the water flow by changing the water flow direction. At that time, the water flow from the yellow tube to the white tube. If the stuck happened near the connectors for the yellow tube, the water pressure only for the yellow tube could be enhanced a lot. In such a case, the yellow tube dis connection could happen. However, we also confirmed that there was no stuck material inside this beam dupmper. The stuck material flowed out and got inside the M6 hole when the water leak started??? 
  • The white type sleeves at the connector were used for this beam dumper that had a water leak. Originally, it had black-type sleeves. The white type could be slippy than the black type. This white type was used when the water stuck happened before.

 

 

Images attached to this report
Comments to this report:
shinji.miyoki - 21:40 Monday 25 November 2024 (31761) Print this report

Rough sketch of the water leak area. The PMC body is originally lifted up. So no water on the PMC body.

Images attached to this comment
shinji.miyoki - 21:52 Monday 25 November 2024 (31760) Print this report

The mitigation of thermal lensing in two EOMs can affect the mode matching to IMC during working mode because EOMs can be cooled by airflow of 30cm/sec? 

shinji.miyoki - 23:36 Monday 25 November 2024 (31764) Print this report

PT01~05 on the PSL room table and PMC/IMC output.

PT04 is the nearest position for the water leaking point and PMC. It clearly shows that the drastic temp change because of the leaking water cooled the optical table near the PT04. So, the beam direction of the PMC output also could change because the PMC body could rotate / teilt due to the optical table deformation. Just after the FB recovery, the beam spot of the PMC refl shift a lot upward in the camera.

PT02 reduced a lot (over 1C) because this was soaked in the leaking water as surrounding periscopes and optics. This could be the main reason why the IMC alignment was destroyed because it is also near the periscope for the IMC input.

 

  • PT01:(Laser): far from leaking water
  • PT02: (Periscope for IMC injection): soaked in water !!
  • PT03:(Pole for GR fibers): far from leaking water
  • PT04:(Near PMC) : near leaking water
  • PT05:(Near Electronics Rack): far from leaking water
Images attached to this comment
shinji.miyoki - 23:37 Monday 25 November 2024 (31765) Print this report

By the way, can we relocate the beam dumper for the IMC refl by using one more mirror to outside area of the optical table? If we can do this, we can avoid water flooding on the table and vibration due to water flow inside the beam dumper. How about fixing the beam dumper on the wall of the PSL room or on the aluminum frame beside the duct to the IMC by using magnetic support/clamp, avoiding accidental crossing of workers? 

shinji.miyoki - 7:32 Tuesday 26 November 2024 (31767) Print this report

In addition, we are operating another chiller for the beam dumper in the REFL table. It is better to check the water flow.

shinji.miyoki - 7:34 Tuesday 26 November 2024 (31768) Print this report
osamu.miyakawa - 11:48 Tuesday 26 November 2024 (31770) Print this report

MIyoki-san and I checked the PSL room this morning.

It seems to be the same as last night, and we decided to move to observation mode and wait for a while until the temperature becomes stable.

Alignment of PMC and IMC were adjusted yesterday under different temperatures, so they should be re-aligned after the temperature becomes stable.

 

Meanwhile, we discussed the air cooling beam dump. The dump accepts until 35W, so the current 20W output is OK.

We will relocate the position of the water cooling beam dump outside of the table as Miyoki-san proposed.

 

If you need to change the connecter of the water tube for beam dumps, basically please use "black" sleeves.

All water tubes used for beam dumps in the PSL room are 1/4 inch. Black sleeves are for inch size but white sleeves are for metric size. Please DO NOT use white sleeves unless you are sure you must use white ones.

 

shinji.miyoki - 17:38 Tuesday 26 November 2024 (31779) Print this report

I checked the water flow of the chiller for the beam dumper in IMC refl. It worked fine, and the water was very clear, in contrast to the water for the PSL room.

Actually, this chiller operation time is very long (~ over 3 years or so).

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