During the commissioning meeting today we discussed what to do about the bad lock acquisition. We decided to try the new SEI config which is in Jim's log, and also to revert the TCS pre-load configuration from 50W pre-load to somewhat less (see entry below). Probably, the pre-load was making too much angular instability in the DRMI; too much lensing -> unstable cavities.
Our DRMI lock acquisition speed is now back to less than several minutes, with a few locks this afternoon happening within a couple minutes. This is great. We need to capture this configuration of parameters sothat we don't wander away from the good place.
The TCS settings were adjusted to a 30 W pre-loading state (last used immediately before the vent) from a 50 W pre-loading state:
| ITMX RH power (W) | ITMY RH power (W) | CO2X power (W) | CO2Y power (W) | |
| 30 W Pre-oad | 0 | 1.74 | 0.2 | 0.6 |
| 50 W Pre-load | 1.10 | 5.234 | 1.06 | 1.72 |
The change to the 30 W preload state was at 05:14:12 UTC
It seems as if the ifo is sensitive to high microseism (>=.4 um/s) with the 50W pre-load settings. Shortly after recovering from the vent we were acquiring DRMI on the order of 5-10 minutes with the 50 watts pre-load settings and it was only until this week that we've had issues locking DRMI. Right now it seems that the combination of the 50W pre-load and high microseism are to blame though there have been some other moving parts so a more thorough investigation may be required.
There is no doubt that this TCS change is helping us lock the interferometer again at 2W. TCS updates are pending as we get the interferometer stable again at 20 W - 25 W input power.
Picture of medm screens during DRMI acquistion and DRMI locked. Triggers are at POPAIR_B_RF18_NORM = 60, while fully locked is ~80, so that is 75% of maximum buildup triggering.
After the November vent we had difficulty with ASC and had to reset our POP and transmon (soft) QPD positions. We thought that this could have been because of the preheating, but reverting the preheating didn't cause us any problems for ASC today.
With the DRMI locked with less pre-heating, I set the digital demod phases for the POP 2-omega channels:
| Old | New | |
| POP 18 | 42 | 46.3 |
| POP 90 | 49 | 57.2 |
Did this by minimizing the Q phase signals using 'z servo'. This assumes that the sidebands in the DRM are balanced, so...