Jennie, Jenne, Keita, Camilla 

Following 76883, we repeated by moving IM1 Pitch and Yaw then IM2 Pitch and Yaw in turn and recentering the beam on the IM4 TRANS QPD using IM3. Went in both directions until we either saturated the suspension or starting clipping on the Faraday. 

Results: We are not close to clipping FI so reverted the alignment to the original (though TJ said these IMs can have hysteresis).

Steps taken:

• Misaligned PR3, aligned PRM (so we can see REFL beam). 
• We tried using DC centering loops but this wasn't easy to implement so we didn't use them: Jennie copied filters from DC centering loops into DC7 FM2 as 2304_Test, we edited ASC matrices for IM4 Trans > DC7 > IM3. Turned on DC7 gain, IM4 trans didn't really converge, tried + / - gains. Not worth our time.
• Plots from the QR code in G2201230 show the beam radius is around 2mm though IM1 to IM4. Keita points out there is other apertures in this path that may be tighter than the FI. 
• For IM1 Pitch and IM2 Pitch and Yaw, we saturated suspensions (IM2 or IM3, details in pdf)  before clipping the Faraday.
• For IM1 Yaw we stared clipping the Faraday just before IM3 saturated.
  • When we went to the middle position between the two clipping edges (and recentered with IM3) the IM4 TRANS NSUM power was the same as the nominal IM1 Yaw position to within 0.1% so we reverted to nominal. 
  • Nominal IM1 Yaw: -384. Clipping edges: -884 and +416. Center or clipping edges: -243.
  • <0.1% change in IM4 TRANS NSUM power between -384 and -243 alignment,  so we reverted to nominal.