Part 1: Rotation of optic

• As reported in my elog yesterday, both the left magnets (UL and LL) seemed too low relative to the OSEM coils
• Eric and I checked the height of the scribe lines using the microscope and found that the scribe lines were low on the left side and high on the right side (as viewed from the AR side) by approximately the same amount, confirming our suspicion that the optic was rotated. The position of the scribe line on the bottom of the optic relative to the bottom-rear face EQ stop also suggested the same
• Eric brought in the bottom EQ stops, and once the wire was slightly unloaded, rotated the optic by the required amount by hand 
• This process took two tries, but we were successful
• Re-checked heights of scribe lines using microscope, and once we were satisfied, re-did the coarse pitch balancing

Part 2: Replacement of holder for top pair of OSEMs

• Eric and I had difficulty removing the UR OSEM-holding screw
• This is the non-silver-coated new variety of screw
• It got to a point where I could neither move the screw in or out, even with the help of a pair of pliers
• I decided to swap out the piece of the suspension tower holding the top two OSEMs (UR and UL) with the same piece from the old ETMX tower that is currently residing on the flow bench at the south end (along with the accompanying piece that overhangs the optic and holds the front-face and top earthquake stops
• I cleaned the piece 3-4 times with acetone, and then a couple of times with isopropanol. I adjudged this to be sufficient as we are going to air bake the tower anyways prior to installation in the vacuum chamber
• I then swapped the pieces:
  • First I brought in the bottom pairs of EQ stops
  • Next, I secured the optic using the three lower face EQ stops
  • Then, I removed the EQ stop screws from the overhanging piece, after which I removed the overhanging piece itself
  • After removing the top-back EQ stop, I removed the OSEM-holding piece from the suspension tower
  • Did the above steps in reverse, installing the new piece
• All went smoothly. This piece does not have a serial number unfortunately
• After this, I re-inserted the OSEMs, and judged the magnet-coil alignment to be satisfactory to proceed further
• We decided to use the old variety of silver plated OSEM holding screws for the top two OSEMs (by choice) and the side OSEM (the new variety is too short anyways). During the course of my work tonight, I found this worked way better. The bottom pair of OSEMs remain held by the new variety of unplated screws. We may want to review whether we really want to use this new type of screws (I believe the idea is to make it easier to tighten and loosen the screws)

Part 3: Fine pitch balancing

• As per the SOS assembly procedure, I turned off the HEPA filters at the clean bench for this part of the work
• Checked that the HeNe beam incident on the optic was level with the tabletop, beam height set to 5.5"
• Proceeded to do the fine pitch balancing the same way as described in yesterday's elog (i.e. no PZT buzzer, just fine touches by hand)
• I was able to converge fairly quickly to a good point in configuration space
• After re-centering the OSEM coils such that the PD output was ~50% of its maximum value (see Attachment #1), I found over a lever arm length of 56" (=1.42m) a beam height deviation from 5.5" by <2mm. This corresponds to 0.7mrad pitching forwards towards the HR side
• The suspension assembly procedure tells us to aim for 0.5mrad, but I think this is close enough for standoff gluing, as this misalignment is extremely sensitive to the OSEM coil positions (although I would say, from Attachment #1, that they are actually pretty well centered)
• The only thing that concerns me is that the LL magnet is still a little low relative to the coil. This can be fixed by shimming if necessary...

Attachment #1: Striptool trace showing OSEMs are pretty well centered (towards the end, I turned on the HEPA filters again, which explains the shift of the traces). The y-axis is normalized such that the maximum displayed corresponds to the fully open PD output of the coils

Attachment #2: Fine pitch balancing optical lever setup

Attachment #3: Tower assembly

Attachment #4: SIDE OSEM close-up

Attachment #5: UR OSEM close-up

Attachment #6: UL OSEM close-up

Attachment #7: LL OSEM close-up (this is the concerning one)

Attachment #8: LR OSEM close-up

We should also check the following (I forgot and don't want to wear my clean jumpsuit again now to take more photos):

1. Wire is still in groove
2. Standoff is sitting on the optic barrel and not on epoxy residue of the guiderod