Hugh, Jim, Hugo,

We measured the level of stage 1 this morning. Results are attached. Stage1 appeared tilted by ~170 µrad. This result is beyond the 100 µrad of the acceptance criteria used during the assembly-validation phase.

We recently changed the shim thickness on locker D. In order to make sure that it is not the cause of the mis-levelling, we measured the level on stage1, just above the locker D when the ISI is locked, and compared it to the same measurement when only the locker D is unlocked. The shift in level is less than 1mil. Hence, the adjustement we made on locker D is not the cause of the mis-levelling we observed.

Changing the shim of locker D is the only serious mechanical modification we made on HAM3-ISI after the suspensions (MC2 and PR2) were approved. We then conclude that the suspensions were tested under the current configuration without being affected by it in a noticeable manner.

We measured the level of stage 0 around the lockers. We did not detect such a mis-levelling there (see attachement).

The assembly validation testing is performed with a ~600lbs pounds on top of the ISI. The mass distribution is very different now that the ISI is loaded with suspensions, optics, and 10kg masses. We currently suppose the new mass repartition would have affected the flatness of the optical table, and thus the level measurement which is performed along its edges.