Sheila Evan Jenne Terra
The IMC length drive has large glitches when only the IMC is locked. The first attachment shows the MC2 M2 length drive durring a quiet time on July 31st, and a glitchy time today. There are glitches present in both traces, but they are much louder in the trace from today. If you look back at data from late July, the glitches have intermittently been present even before we started having trouble locking, so this is probably not the main reason we can't lock.
The second attachment shows 15 minutes around the time of the July 31st trace, when the glitches transition from being quiet to loud.
Daniel, Sheila
These glitches appear when green light starts flashing in the arms. The COMM PLL sometimes see a green flash, and tries to lock as you can see in the control signal in the top panel of the attached plot. This would be fed back to the mode cleaner if ALS COMM was locked, but that feedback is disabled. The PLL trying to lock moves the COMM VCO, which through some kind of RF coupling similar to the cause of the whistle glitches causes the mode cleaner glitch.
Once we are fully locked we park the VCO so this should not be a problem in full lock and should not be related to the glitches we see after changing gains on the CM board
