Rahul, RyanC

Over the past few weeks we've prepped the two basic HXDS assembly (structure sn 035, alog88828 - OMA3 with B2-03 optic, and structure sn 029, alog87998 - OMA2 with A1-03 optic) that we received from LLO. Rahul and Camille assembled these PSAMs at CIT. We attached the wires using the provided HDS Bottom Mass Wire Plate ASSY D2000395 setting the top blade height first using the blade height gauge then feeding the wire down, and the bottom mass (PSAM) with its fixture assembly plate. The wire clamps really wanted to clock when I was doing the final turn, turn and a half on their fasteners so I had to tighten them very slowly. For OMA2 we had some trouble trying to remove the intermediate mass fixture plate D2000230 to replace it with the BOSEM Cam Adj Mtg ASSY as there was a stuck dowel pin. The fixture plate was a V1 version which did not have the emergency release feature that the later version has. We brute forced it out without damaging any components or wires but the intermediate mass shifted a decent amount despite my efforts to keep it still. OMA3 did not have this issue as it was as the V2 plate.

Once we had OMA2 fully assembled, we balanced it then brought it over to the test stand and connected the four OSEMs to the top stage. This first suite of phase 1a measurements was done without the M2 PSAMs cable connected.

The OLV counts were as follows (we later swapped LR and UR, which is reflected below) for OMA2:

UL: 28460 UR: 31900

LL: 29720 LR: 30860

The data/templates live in: /ligo/svncommon/SusSVN/sus/trunk/HXDS/X1/OMA2/SAGM1/Data

and the result pdfs are in: /ligo/svncommon/SusSVN/sus/trunk/HXDS/X1/OMA2/SAGM1/Results

I ran 3 sets of measurements on Wed with a bw of 0.02. The first measurement 2026-03-25_1730 showed some weirdness with LR and lots of cross coupling from Length into Pitch and a bit into Yaw, the shapes were a little different, as well along with the magnitude but that's probably from the coil driver gain. Rahul then swapped the LR and UR OSEMs and double checked the centering, and I ran another measurement 2026-03-25_1900, which looked about the same. Rahul then went and improved the balancing as best he could (the masses were pitching a bit) and I ran a final measurement 2026-03-25_2130.

Overall the Transfer Functions look ok but there's still room for improvement. 

On Thursday Rahul balanced and set up OMA3 on the test stand. Unfortunately while manipulating OMA2 one of the bottom M2 stage wires broke, so we will have to replace it and remeasure it next week.

The OLV counts were as follows for OMA3:

UL: 27030 UR: 32100

LL: 27500 LR: 28900

The data/templates live in: /ligo/svncommon/SusSVN/sus/trunk/HXDS/X1/OMA3/SAGM1/Data

and the result pdfs are in: /ligo/svncommon/SusSVN/sus/trunk/HXDS/X1/OMA3/SAGM1/Results

This set of transfer functions, 2026-03-26_1900 also looks ok and similar to OMA2, see the comparison plot of OMA2 and OMA3. Both measurements shows some weirdness with LR that is not seen in an OSEM noise spectra that we're still looking into.

The next steps are to repair the bottom wire on OMA2, attach PSAMs cables, remeasure then fine tune both OMA2 and OMA3.

Tagging EPO for Corey for the pictures. I'm realizing I only have pictures of OMA3, I might comment with more photos on Monday of OMA2.