Last night TJ and I tried some TCS tuning of CO2X to see if we could fix some of the high frequency noise couplings. Things we learnt:

• ADS doesn't seem to like the same scale of TCS change and I had been doing before. The other night I changed SR3 heater with the 36W test and it started trending away. Then last night when I increased the CO2 it also got unhappy and got itself into a glacially paced oscillation. It was an odd oscillation, it seemed to get a strong kick each time it got close to zero... I left it on at the time as each time it looked like it was sorting itself out, eventually when the CO2X heating had cooled down it was fine.
• The violin mode last night seemed to be ringing up since the start of the lock before any TCS changes were made last night
• Increased CO2X from 0.6W to 1W (the other night I manged to push this up to 1.2W). During this time:
  • RF18, RF90, kappa_c decreased
  • PRG, cavity pole increased
  • Decreasing lines: 9MHz RIN, ~70Hz and 3200Hz intensity noise, 4500Hz frequency noise
  • Increasing line: ~70Hz frequency noise
• Decreased CO2X from 0.6W to 0.4W
  • TJ thinks things were getting more unstable
  • ADS looked ok
  • ASC: DHARD P/Y and CSOFT P look like they were getting noisier. The noise didn't reduce after turning the CO2 backup again.

I haven't demodulated all the lines and data yet but I'll make plots later.

Overall the noise couplings got better with more CO2X, similar behaviour to what we saw at 30W as we're giving a CPX a more positive lens to match the extra heating in ITMY. This time we did see some changes in the frequency noise coupling in the bucket, previously we did not see that. Although the noise couplings got better the sideband matching in PRCL/SRCL got worse. Both RF18/90 were reducing and AS_C sum was increasing. PRCL to arm matching seemed to get slightly better though as PRG increased a small amount, ~0.1.

Less CO2X just made everything worse, apart from frequency noise coupling in the bucket.