Summary:

TMSY pitch and yaw alignment tweaked to increase POP_A_LF, saving the lock.

Details:

After JeffK and I saw that POP_A_LF was dropping, I looked at the H1 alignment over the 27 hour lock, and focused of PR3, ETMX, and TMSX.

After looking at the trends, I proposed the idea to JeffK that we might be able to save the lock by aligning TMS, and he suggested TMSY, based on previous work by Kiwamu.

When I compared TMSX and TMSY alignments over the 27 hour lock, I found that TMSY alignment changed by -1urad in pitch and +0.5urad in yaw, when measured from the start of the decrease in POP_A_LF.

To compare, TMSX alignment changed 0.02urad in pitch and 0.05urad in yaw.

I started by raising POP_A_LF  with TMSY yaw, and stepped the alignment slider by 0.05 at first and then increased that step size to 0.2, with a ramp time of 20 seconds, and made a step about every 4 minutes, which gave the ASC time to recover.

After some improvement in POP_A_LF, I switched to aligning TMSY pitch.

When I was done, POP_A_LF had increased from 14850 to 16100.

Plots attached:

• 27 hour plot of TMSX, TMSY, and POP_A_LF
• 6 hour plot of the fix, showing TMSY alignment sliders and position, and POP_A_LF
• 27 hour plot of ASC red QPDs at EX and EY, pitch and yaw, and POP_A_LF
• 27 hour plot of ASC red QPDs at EX and EY, sum, and POP_A_LF

Time history of this lock:

• Jan 9,  00:13:12UTC - H1 reaches Low Noise, start of this lock
• Jan 9,  ~19:00UTC - POP_A_LF starts to fall
• Jan 10, 02:33:40UTC - I start tweaking TMSY alignment - POP_A_LF is 14850
• Jan 10, 03:14:46UTC - H1 back in Observe - POP_A_LF is 16100
• Jan 10, 04:20:48UTC - POP_A_LF is still at 16100

- Cheryl, JeffK, Kiwamu