[Tanaka, Yamamoto, Yuzurihara, (miyoki, uchiyama: remote)]

[Summary]

There seems to be a stuck in the water circulation path for the beam dumpers(BDs). So these beam dumpers were not cooled by water from the chiller. As a result, the temp at the beam dumper at the REFL increased, then the interlock was triggered by its thermometer.

[What we did]

Firstly, we checked the water chiller for the beam dumper. The water level was slightly lower (The top of the metal circulating tube inside the water vessel was slightly above the water level). The chiller itself was on, and the temp setting was 15C(OK). At this moment we did not check whether the water was circulated or not.

Secondly, we checked the interlock box near the entrance door of the PSL  room. We found the interlock was activated with a red LED light. Thirdly, we checked the sealing of the thermometer on the back of the beam dump. The contact of the thermometer seemed to be good.

Then we reset the interlock successfully. After that, we confirmed that the warning message in the FB control application has not vanished and the temp shows ~50C. Then we closed the application and restarted it. The warning has vanished. However, the temp showed ~3C and it became ~ 50C again after pushing the enable button in the application. So, we closed the application again, and made off/on procedure for the FB laser amp itself. After starting the application, the temp showed ~20C and we could keep this temp after enabling the FB laser.

We increased the current to obtain 10W output.

After that, we started the investigation again on the water chiller system for BDs. Tanaka-kun noticed that the air bubble in the water tube did not flow at all. Also he touched the REFL beam dumper and he sensed relatively hot. Then we suspected that there was no water flow in the chiller system. We tried on and off the chiller. Tanaka-kun noticed that the air bubble position shifted a little bit every on/off action and that the tube itself showed a little bit of trembling. However, we could not realize the smooth flow of the air bubble.  Then we checked whether there was returning water flow just before the chiller or not even if the chiller seemed to try to flow water (We sensed some vibration in the chiller itself after pushing the pumping enable button). Then we confirmed that no water returning.

Firstly, we suspected there was something wrong in the chiller itself. So we replaced the chiller with a new one. However, there was also no returning water from the path in the PSL room. To check the chiller itself, we replaced the tube for going from the chiller to the PSL room with a new one, and checked whether there was water output or not. Then we got water flow output. So we concluded that there seemed to be a stuck in the tube-path for BDs in the PSL room.

Because stuck search in the PSL room is a hard work, we gave up today's recovery work.

The FB laser amp was left to be stopped. The seed IR was on.

[to do]

To check the stuck in the tube path in the PSL room, we need to 

• change from OBS mode to Working mode for the PSL room for the long activities.
• remove all parts on the tube path including BDs not to spoil the PSL room with water
• check the stuck point in each part.

If we want to recover the FB at 20W output temporally, we can put air cooling type power meters (50W max and 150W max that we have) instead of these water cooling type beam dumpers. In this case, the interlock system will be temporarily disabled.