With Aso-san, Hirata-san and Yano-san.

Summary: we set the mirror height according the new height markings.

Pictures can be found in the album SR2 Remedying work after O3.

Tomaru-san recently made new markings in vacuum chambers and pillars indicating what the suitable height of the mirrors are. These new markings are slightly different to those made  by Terada-san long ago. The work today was to adjust the height of the mirror to the new marking. It happened that now we needed to raise the pre-isolator.

• We opened the top of the chamber, locked the IP and locked F0 very close to zero, which is its nominal position.
• We set the positions of the F1 and BF keystones close to zero using coil-magnet actuation.
  • F1: -2100 counts,
  • BF: -1100 cnt,
  • Temperature: 23.4 degrees.
• We measured the height of the mirror with respect to the new marking: it was 1.6 mm below it.
• We turned off the actuation and raised the pre-isolator by approximately 1.6 mm. The jacks have a M42 X 2 mm, so we moved it by 3 steps of 90 degrees plus one of around 22.5 degrees, which is close to 288 degrees = (1.6mm / 2mm ) X 360 degrees.
• After turning the actuation on in F1 and BF, we measured the height of the mirror again: it was 0.15 mm below the target. We decided this was good enough.
• We then released the F0 and the IP and turned the actuation off in the BF and F1.
• We leveled the IP by moving the jackes slightly until it was close to the setpoint.