Sheila, Ibrahim, Jenne, Vicky, Camilla
After Ibrahim told Sheila that DRMI has been struggling to lock, she checked the POP signals and found that somethings been drifting and POP now appears to be clipping, see POP_A_LF trending down. We use this PD in full lock so don''t want any clipping.
We has similar issues last year that gave us stability issues. These issues last year didn't have "IMC" lock-losses so we think this isn't the main issue we've having now but maybe effecting stability.
Trends showing the POP clipping last year, and now. Last year we moved PR3 to removing this slipping while looking at the coherence between ASC-POP_A_NSUM (one of the QPD on the sled in HAM3) and LSC-POP_A (LSC sensor in HAM1): 74578, 74580, 74581.
Similar coherence plots to 74580, for now are show the coherence is bad:
- It's got worse since July, ca see as step down once we moved PR2 in 78878. Compare Green (July 1st) then Red (July 10th), then Blue (now), plot here.
- It's been bad since the emergency vent recovery in August plot here.
- The increased coherence seen now <1Hz is the micoseism being elevated.
Sheila is moving the PRC cavity now which is improving POPAIR signals, plot attached is the ASC-POP_A_NSUM to LSC-POP_A coherence with DRMI only locked before and during the move. See improvements. Sheila is checking she's in the best position now.
We have been holding 2W with ASC on before powering up, and using the guardian state PR2_SPOT move, which lets us move the sliders on PR3 and moves PR2, IM4 and PRM sliders to follow PR3.
Moving PR3 by -1.7 urad (slider counts) increased the power on LSC POP, and POPAIR 18, but slightly misaligned the ALS comm beatnote. We continued moving PR3 to see how wide the plateau is on LSC POP, we moved it another -3urad without seeing power drop on LSC POP, but the ALS paths started to have trouble staying locked so we stopped there. (POP18 was still improving, but I went to ISCT1 after the OFI vent and adjusted alignment onto that diode 79883 so it isn't a nice reference). I moved PR3 yaw back to 96 urad on the yaw slider (we started at 100urad), a location where we were near the top for POP and POPAIR 18, so in total we started with PR3 yaw at 100 on the slider and ended with 96 on the slider.
