[Rahul, Keita, Betsy, Koji]

Preparation work to extract the existing OMC has been completed. We will continue with the OMC extraction tomorrow morning.
The overall work procedure for the OMC replacement is summarized in G231106 https://dcc.ligo.org/LIGO-G231106.

= OMC shroud panel removal =

While waiting for the beam from the squeezer to come, we started the removal of the OMC shroud panel in parallel. The work was done along with the procedure E1600164.
The removed panels were placed on a stainless steel table in the HEPA booth of HAM6 (Attachment 1). The panels were not covered to prevent accidental placement of objects on them.

During the work, a beam dump was removed from the table to make the removal work possible. This beam dump is to kill one of the weak transmissions of the OMC.
Betsy took the photo record of the location, but it is safely trivial how it should be aligned.

= SQZ beam marking and alignment =

The beam was delivered to HAM6 and was pinned down with two irises on the ISI table.
The irises were placed just after the beam entered HAM6 (next to OM2) and just before OM1 (next to the fast shutter).
This means that these indicators are not affected by the alignment in HAM6.
They were placed by eyeballing, so their precision was as such. By default, both the irises were set to the maximum opening.

Next, the beam alignment was servoed towards the WFS heads using the DC centering ASC loops.
As soon as the control was applied, both QPDA and QPDB of OMC showed significant signals with total light level of ~1e-3 (Attachment 2).
When the light was blocked (at the squeezer?), the value dropped to almost zero, confirming that this was a real beam.
This is very good news as we'll be able to find the beam arrival using the OMC QPDs when we try to align the new OMC.

= Holding suspension mass =

Next, we proceeded to hold the suspension masses. Rahul and Koji worked in the chamber on the ISI table for the following operations.

To hold the intermediate mass:

• First, the top blade was fixed with stopper screws.
• Next, we tried to fix the middle mass with two 1/4-20 nuts, but this caused some wobbling of the suspension. So, we first decided to fix the middle mass with smaller side EQ-stops. This process has not been described in E1600164. (to be updated)
• Once the middle mass was fixed horizontally, the vertical dof was also fixed firmly with the small EQ-stops and the 1/4-20 hex nuts.

Then, moved onto fixing the OMC:

• The bottom EQ stop for the OMC was left as they could not touch the OMC. The side (long side) EQ stops were extended and are holding the OMC horizontally.
• The Top EQ stops for the OMC were removed by removing the L-shaped brackets on both sides.

= Removing the electronic cables from the OMC =

Upon removing the electronics cables, one person held the cable harness on the OMC breadboard to prevent the OMC from wobbling too much.
The removed cables were wrapped around the top part of the suspension frame to keep them out of the way of the further work.

At this point, it was just at 5pm, so we exited from the chamber.

Next Steps:

• Extraction of the OMC
• Migration of the balance masses to the new OMC
• Final cleaning of the new OMC
• New OMC installation