During the latter part of the day, Louis and I tried to get back to resonance, but have yet to get there. First, we had problems with TR carm (again), and then we struggled at the carm offset reduction.

For TR CARM, we thought the gain might be a bit low in start_tr_carm, so we upped the analog H1:LSC-REFL_SUM_A_IN1GAIN by 3 dB. This seems to help! Louis also increased the time in the servo to 10 seconds.

CARM_OFFSET_REDUCTION problems:

• We ran carm offset reduction and failed. We tried stepping up slowly in the offset and adjusting the gain, but kept losing lock. We found we can step to -35 offset and a gain of 60, and then up to -40 and a gain of 61. This is 3 dB lower than the original final gain of 86, which makes sense based on our gain increase in TR carm.
  • Even though this is guardianized, this still seems to fail unless done by hand. I don't know why because the guardian code should be exactly replicating what I do by hand: step to -7, wait, step to -12, wait, engage darm boost, step to -35 and 60 gain, wait, step to -40 and 61 gain, engage reflbias boost
• I have tried stepping the alignment around to see if I can make the recycling gain better.
  • Looking at the transmitted powers both yesterday and today, I am concerned that the refl power is too low and that we have poor recycling gain.
  • In O4c, I measured arm transmission and refl ratios to see if our carm offset reduction sequence was having a problem, see here. Turns out we were fine at the time. But we can compare those powers to now, reminder we had recycling gain of about 54.
  • For arm transmission of 800, the refl power should be about 1.96 mW, compared to 3.7 mW off resonance, so a ratio of 0.52.
  • Tonight, for a transmitted power of 800, refl power is 1.3 mW compared to 3.5 mW off resonance, so a ratio of 0.37. We saw similar powers last night, although we were able to make it all the way to resonance. This is still in the region of a gain of 30, but that does seem low compared to a year ago.
  • I tried stepping the DHARD alignment around, but it did not improve the refl power. CHARD alignment seems to help, but it's a small improvement. Since the improvement is so small when the transmitted power is low, I think I stepped the wrong way and caused a lockloss by reducing the carm offset with very low recycling gain.
• I tried one more time to walk CHARD around, looked like I was going in the right direction, but we still lost lock.

We had one lockloss at carm 5 pm after completing carm_offset_reduction by hand. Don't know why, but this was another state we sometimes had to carefully do by hand.

Want to reiterate that the IMC is still being fussy when relocking.