Summary

TMSX needs to be YAWed by about -250 urad (YAW slider from -329 urad of Feb/06 X arm peek to -585 urad today) to make the ALS X beam retro reflect by ETMX.

Old ERMX wedge seems to have been about ~590 urad, thus deflection should have been (1.46-1)*590=270 urad horizontally, but now the wedge is entirely gone.

We know that ETMX angle is pretty good as of now within ~+-80urad or so from PCal reflected beam. We know that TMSX suspension didn't change angle by O(100urad) since February.

Unfortunately, with the new offset TMSX suspension DAC is already railing, so we need a physical rotation to relieve it.

Old ERM wedge

Old ERM spec is pretty loose, 0.04+0.04-0.03 deg = 700+700-500 urad (in horizontal direction, it seems).

In the case of old ERMX, which is ERM-02, the Vendor report (C1001321) shows that the edge at 180deg position is 0.2mm thicker than the reference edge at 0deg, so I'd guess the wedge is 0.2mm/340mm =590 urad. The same report says something about parallelism of 0.02mm but I don't know what it means. There is also GariLynn's transmission data E1200019 but I don't know if Zernike Tilt coefficients on the report represent the wedge or not.

IF the wedge was indeed ~590urad, using n~1.46 at 532nm, the deflection should have been 271urad before ERM replacement.

(For ERMY 0.25mm/340mm~735urad, deflection ~340urad, on the same order as ERMX, Vendor report C1001320).

What was done

After Betsy and Travis are done with ETMX oplev and confirmed that PCAL beam reflection is right on the detector within +-1mm or so (which means that the ETMX angle is good within of  ~+-1mm/6m/2=+-80mrad), I fired up the ALSX laser, turned on the QPD centering, went in to the chamber, removed the ERM cover, came out and changed the TMSX alignment offset to obtain retro-reflection. I had to basically rail F2 and F3 coil that are used for YAW.

There apparently was a big YAW shift, but I don't see any M0 stage jump nor drift since February. I and Corey moved LF, RT and F1 BOSEMs at some point, but the actuation of a BOSEM should have much smaller dependence on the magnet depth than the sensing, and anyway these shouldn't and didn't affect YAW. See attached.

After this ERM cover was put back on, ALSY was turned off, and EY station was put back in laser safe.

Betsy reported that they ran a quick transfer function and saw no touching/rubbing.

What about Y?

TMSY Yaw offset used to be pretty small (between 0 and +10urad last year when ALSY was regularly locked), but after ERMY swap we had to set the YAW offset to -217 urad (40793). As was noted above, IF the wedge could be read off of the thickness measurement by the vendor the deflection should have been 340 urad. Not as satisfying an agreement as X, but still on the same order.