Jenne, Georgia

Lately when we have tried to move the OMC for dither alignment, or to minimize the output jitter coupling, we have been railing the OMC suspension. Most of the drive was in the length DOF, and full lock we were sending ~38k counts to SUS-OMC-M1_ASC_L_OUT16.  Edit: the drive which is saturating the OMC coil drivers is actually pitch! On Friday we pico'd AS_B to offload some of that drive on OM1 and OM2 (via the DC centering loops).

To get set up:

• We set the interferometer in single bounce configuration (10W)
• turned on the AS DC centering loops
• engaged the OMC ASC using the OMC LOCK guardian
• locked the OMC (which involved moving the OMC PZT to find the resonance by hand, and manualling the OMC guardian to OMC_LOCKED)

To determine and set the pico position:

• We added DC offsets to AS_B in pitch to check where we would need to pico to offload the OMC sus - an offset of -0.3 seemed good (see first attachment)
• We turned off the offset, opened up the DC centering loop, and used the pico motor to take the beam to the same position as it was on AS_B when we had the offset engaged.
• The pico Y position went from 13000 cts to ~14000 cts.

Looking at our long lock from the weekend, the length asc signal was still the largest at around 10k counts, but at least we pico'd in the right direction. We're hopeful this is enough that we can switch to the OMC dither alignment without causing lockloss.