M. Takahashi, Miyoki, Akutsu

Summary

Detached the thick heat link connecting between the high-power beam dump and the copper flange.

Details

As reported in 24203, it has found that the thick heat link connecting between the high-power beam dump and the copper flange (JGW-E2113385) would become a critical path to transfer environmental perturbation to angular jitter of the input beam, and somehow eventually appeared at DARM. So we determined to remove it.

The relevant chambers (IFI-IMM-PRM) has been already got back to atomospheric pressure in the last week (24259) with dry clean air. IMMT1T QPDs were used for reference monitor to know to what extent we could exert torque to the works. Anyway, what we did were:

1. Detached a window viewport (labeled C-2-4) for IFI camera, which had not been used for a long time, as it could not see any meaningful image so much. The camera with a stage was also detached.
2. Through the opening for the camera window, accessed four M8 screws that had been fixed the heat link to the relevant structure on the optical table in the IFI chamber, and detached them all.
3. I tried to move the relevant end of the heat link but I found it was heavy and difficult. So we changed our strategy; once keeping this end left on the table, we loosened screws fixing the copper flange (labeled C-2-3-2), and took out the flange with the heat link at once. For reference in the future, this particular work needed at least three people; two people to support the flange weight, while one support the end of the heat link by accessing it via the ex-window viewport.
4. Detached some structures including the heat link from the copper flange (Fig. 1); we firstly thought to use a new SUS flange beacuse now there is no meaning to use copper flange as it is disconnected with the heat link. But we found this SUS flange did not match to the currently-installed K400 flange of the chamber. It seems the copper flange is special and a non-standard one, unfortunately. So we determined to re-use this cupper flange without the heat link. We used a new viton o-ring, anyway.
5. Got back the copper flange to the IFI chamber, and also the camera viewport flange (Fig. 2). This time we did not get back the camera with the stage as it would not be used any more.