Reports until 17:24, Thursday 07 December 2017
H1 TCS
jason.oberling@LIGO.ORG - posted 17:24, Thursday 07 December 2017 - last comment - 09:00, Friday 08 December 2017(39685)
TCSx and TCSy Realigned

J. Oberling, T. Shaffer, T. Sadecki, B. Weaver, A. Brooks (remote support)

Today we completed the initial alignment of the TCS tables (after Greg placed them in their new positions last week) to their respective in-vacuum mirrors.  Both tables were aligned via the following steps:

That being said, it wasn't that easy.  Both alignment lasers needed to be realigned to the irises.  In fact, the alignment laser for the TCSy table needed to be installed before it was aligned.  The real problems, however, came when attempting to align the beam through the ZnSe viewport and onto the 1st in-vacuum mirror.  Regardless of how we adjusted the periscope mirrors, we always ran out of range before we could center the beam on the viewport and the 1st in-vacuum mirror.  The top periscope mirror (TPM) is bolted to a plate, that then bolts to the periscope structure itself via slots in the plate; this plate can therefore be moved up and down on the periscope structure (the drawing for the periscope assemble lives at D1200953).  We tried moving the TPM up and down, but regardless of its position on the periscope structure, we always ran out of adjustment range before the beam was aligned.  The problem is due to an apparent design flaw in the plate.  The plate holds the TPM at a fixed angle, and this angle is apparently not the correct angle for properly aligning the beam.  In order to center the beam on the ZnSe viewport and the 1st in-vacuum mirror, we had to remove all the screws from the TPM plate except for one, rotate the plate on the periscope structure, and secure it with whatever screws lined up.  This was necessary for both TCSx and TCSy.  TJ has pictures of the results that he will post as a comment to this alog.  Long story short, the TCSx TPM is now held on by 2 screws and 1 dog clamp, while the TCSy TPM is held on by 1 screw and 1 dog clamp.  We are not in love with this solution, but it was the only way we could align the beam to both the ZnSe viewport and the 1st in-vacuum mirror.  We emailed Aidan about this and he informed us this was not too surprising due to the table being further away from the chamber.

Once we had the beam in-vacuum, Travis and I entered the chamber and, with TJ assisting from the outside, we aligned each beam to its respective CP.  The alignment from the 1st to the 2nd in-vacuum mirror was trivial, but adjusting the 2nd in-vacuum mirror to align the beam onto the CP was very difficult.  The mirror has 8 screws that are arranged in what appears to be a pattern that allows for push-pull adjustment of the mirror alignment, but in reality that doesn't work at all.  All the screws screw directly into the mirror, so there is no push-pull.  The only way we could reliably align this mirror was to loosen all the screws, and then slowly re-tighten them one at a time in such a way that the beam remained centered on the CP.  This was made difficult by the fact that tightening/loosening each screw had a counter-intuitive effect on the beam alignment; i.e. we would tighten a screw on the right side of the optic expecting the beam to move right (since we're pulling the mirror in that direction) but it was a toss-up as to whether the beam would go right, left, or just not move at all.  After several iterations of tightening and loosening screws we finally got the beams aligned to the center of their respective CPs.  This completes the initial alignment of the TCS tables to their in-vacuum mirrors; a fine alignment will be done once the HWS table is re-installed and aligned and the CO2 lasers are hooked up and running again (the HWS is used to image the heating provided by the CO2 lasers, and the TCS TPMs are then adjusted to center the CO2 beam on the CP).

Comments related to this report
thomas.shaffer@LIGO.ORG - 09:00, Friday 08 December 2017 (39690)

TCSY & TCSX top periscope mirror mount pictures are attached.

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