Sheila, Stefan

The green arm maximum build-up had been trending down for a while to about 500cts, so we decided to do an arm alignment from scratch today.

Step 1: Baffle PDs
- We used the single shot beam to find the baffle PDs:
         TMS PIT    TMS YAW
  PD1    220.0      -226.7
  PD4    289.3      -288.6
  Center 254.65     -257.6
  
  PD1 is H1:AOS-ITMX_BAFFLEPD_1_VOLTS, and PD4 is actually H1:AOS-ITMX_BAFFLEPD_3_VOLTS 

Step 2: Follow with the arm
- We still had some fringing at the old TMS alignment (P 279.3, Y -245.3 - yes, that's 27urad from the new position...)
- Thus we stepped TMS first in pitch and then yaw, and roughly followed with the ETMX and ITMX.

Step 3: Arm dither: Control ETMX and ITMX instead of ETMX and TMSX
- We changed the feed-back scheme to leave the TMS untouched, and only align the arm to the input beam.
- This was done by feeding back PZT1 dither (DOF2) to ETMX, and PZT2 dither (DOF3) to ITMX.

Step 4: Move PR3 to center the green transmitted beam on the first reference iris on ISCT1.
- The new (good) PR3 alignment is
  PR3 P: -245.0  Y: -253.28

Step 5: Realign the green ISCT1 path
- We aligned the camera (and marked the spot on the monitor), realigned the transmitted green DC PD, and tweaked the COMM beat node up.


With this scheme we got about 915cts of green transmitted light - more than ever.


Step 6 (TBD): Diagonalize the dither drive matrix
- Evan and Yuta will do this soon.