J. Oberling, R. Crouch

In talking with Calum about the upcoming pre-deintall BS measurements, I realized that in the middle of JAC install I completely forgot to write an alog about the WBSC2 support tube FARO survey Ryan and I did at the beginning of February.  So, here it is.

Following the same procedure we used to survey the support tubes for WBSC3 and the +X ends of WBSC2 (alog 88620), we surveyed the -X WBSC2 support tube ends.  The results are shown in the 3 attachments; the first 2 are in the LHO Global Coordinate system and are the images I will be discussing.  The 3rd attachment contains all info from the first 2, but in the Corner Station building Local Coordinate system (included for completeness; for more on LIGO coordinate systems, see T0900340).  The first attachment shows the surveyed locations of the support tube ends, while the 2nd shows information regarding the midpoint location of the support tubes and their angles w.r.t. the IFO axes (the line shown represents the centerline of the support tube created from one end point to the other; the Nominal column (Nom) comes directly from the CAD model, while the Measured column (Meas) is our measured data.  Some interesting things to note here:

• Both support tubes are shifted in the -X direction, with the +Y support tube shifted 2.3mm more than the -Y support tube.  This is seen in the Midpoint X row in the centerlines image (2nd attachment).
  • This implies a CCW yaw of the WBSC2 cartridge assembly, in addition to the -X position shift
  • Averaging out the shift, this implies a -2.6 mm shift in the X axis position, and a 1.36 mrad CCW yaw
• My expectation was to find the support tubes too low in their Z axis position by ~2.5mm, but that is clearly not the case.
  • The BS SUS is the same length as the QUAD SUSs, but the BS sits lower in the coordinate system than the QUADs do (-82.9mm vs -80.0mm); this difference was to be made up with HEPI (i.e. shifting the support tubes lower), since physically making the BS SUS longer isn't exactly practical
  • The support tube end survey in the 1st attachment show the ends are not lower by ~2.5mm as expected, but rather fairly close to the nominal Z axis position
• No real comments re: Y axis position, this looks good

Now keep in mind that the support tube locations may not be indicative of a misalignment of the BS optic itself.  When we installed this we only cared about putting the BS where it needed to be, and HEPI (and by extension the support tube ends) was wherever it (they) needed to be to support that.  We will be taking measurements of the BS SUS cage and the optic itself once the corner is vented (likely to be one of the 1st activities after the vent), and we'll know more about the location of the BS optic once we have done so.