cheryl.vorvick@LIGO.ORG - posted 20:33, Thursday 05 October 2017 - last comment - 09:13, Friday 06 October 2017(38913)
ROM RH2 repositioned and realigned to previous beam position as it leaves HAM2
ROM RH2, which sits behind IM1, and steers the IMC Trans beam to IOT2L, was repositioned and realigned today.
As found, with a well aligned IMC that was flashing 0-0 and 1-0 modes, which has beams that are well centered on the IMC optics, the beam coming off of ROM RH2 encountered an OSEM cable on it's path off of HAM2.
The upper right IM1 OSEM cable was hanging down in front of the mirror, and clipped about 1/2 of the beam coming off of the table.
For a temporary fix, I used an aluminum strip that was not effectively holding the cable to a doc clamp, to hold the UR OSEM cable to the UL OSEM cable, in order to give the beam from ROM RH2 clear passage.
This was a temporary fix, and the long term fix is being worked on.
- Keita, Cheryl, Ed
IM1 trans woes finally explained.
This beam was always clipping and was getting worse. We thought that we knew why but it was uglier.
1st attachment shows that the IM1 trans beam, when IMC beam is well centered on MC3 and IM1, is half blocked by the OSEM cable. Somebody thought that threading through the cable mid-air is great. If the beam moves to the right a bit, the beam will be completely blocked.
2nd attachment shows how close to the edge of the steering mirror the beam is when the beam is centered on IM1. As the beam moves to the left, the beam will be clipped and eventually will entirely miss the steering mirror before being clipped by the edge of IM1. I think that's how the IMC was aligned in late O2.
3rd attachment shows the beam path from another angle, showing the cartoon of the beam path and clipping points. I doubt that it was possible at all to exit cleanly here at any point in time.
4th attachment shows the temporary solution to route the problem cable over the top OSEM. After taking this picture, we moved the steering mirror so the entire beam is caught as far as the beam clears the back edge of IM1.