J, Oberling, B. Weaver, T. Sadecki, T. Vo

Last Friday we took a look at the ITMx ACB alignment and found it to be off laterally by +7.8 mm, which was a shift of +8.3 mm compared to the ACB lateral position error from the original alignment (-0.5 mm).  Looking at the HEPI moves made last week (+1.3 mm lateral, 1.25 mrad CCW => ~2.5 mm lateral at the ACB) explained 3.8 mm of the +7.8 mm error, but we still couldn't explain the last 4.5 mm.  Betsy, Travis, and Thomas looked at the ACB and compared it by eye to other "more square" things in the chamber and found that the ACB visually looked like it needed to yaw CW and pitch down (there are no marks or monuments on the ACB to assess pitch and yaw).  Possible after all the swinging back of the ACB for the recent lower structure replacement work it didn't return to its original pitch/yaw; as previously mentioned there are no visual indicators on the ACB for aligning pitch/yaw.  We therefore pitched and yawed the ACB until it was aligned to the ITMx within the ±2.0 mm tolerance.  Another visual assessment of the ACB showed it to look much more square with everything else in the chamber.  The current alignment errors of the ACB, w.r.t the ITMx, are:

• Lateral: +0.1 mm (West)
  • Tolerance: ±2.0 mm
• Vertical: +1.1 mm (high)
  • Tolerance: ±2.0 mm