R. Takahashi, Miyo, K. Tanaka, Akutsu
As there are several known strange behaviors for the MCo suspension, Takahashi-san revisited the MCo suspension and tweaked the IM-RM, but no improvement in terms of these behaviors. Strange.
The MCo suspension has several strange behaviors:
- The picomotor sometimes mixes the DoF (but this might be the same for the other IMC suspensions) by observing with oplev.
- The picomotor sometimes refuses to move.
- Even closing the chamber flange at +X with an aluminum foil tilted the MCo in yaw by 100-150 urad! The sign of the tilt sometimes changes.
- Miyo-kun found a strange feature in the TFs from each one of the coil-magnet actuators (H1, 2, 3, orr 4) on MCo to oplev YAW.
So Takahash-san and I revisited the MCo suspension this evening, and that was a beginning of a nightmare.
First, Takahashi-san found the IM was too close to IM-RM in the -X direction, so he tweaked the IM-RM in a brute way (but this is the regular way according to him... I was a bit shoked); he bended the supporting bars for the IM-RM with a monkey wrench so that the IM-RM was re-balanced in a nice atitude. When he finished, I found the oplve beam was totally out of the QPD in yaw (sum is almost zero) and illuminated one of the electric pin of the QPD! I immediately tried to move the yaw picomotor, and the beam spot could move in the first place, but for some reason it won't move any more when it reached at a certain point.
Then Takahashi-san again saw the IM and IM-RM were again very close in the +X direction. He did the same way to relocate the IM-RM. Then I found the oplev beam moved much in the opposite direction! Anyway, again, the beam spot illuminated the other edge of the QPD (but this time the sum is large), and so I again tried to move the spot by picomotor in yaw. Finally it came back to the center of the QPD, although there were issues as already listed above... the picomotor in yaw suddenly become irresponsible or moved in very small amount... Anyway, fortunately, the IMC transmission beam profile also recovered.