Here is a hypothetical scenario which could make the glitches in the LSC error signals. It can be considered as a 4 step phenomenon.
(1) up conversion noise due to a large motion at 3 Hz
=> (2) rms level exceeds the line width (a.k.a. linear range) in some LSC sensors
=> (3) unlocks some of the DOFs in a moment
=> (4) glitches due to the short unlock.
- - plan - -
In order to check this hypothesis the low finesse PRMI must serve as a good test configuration.
What I will do is to gradually decrease the offset in MICH such that the finesse of PRMI becomes higher.
And at each different finesse I will check the spectra, glitch rate, and etc.
Low finesse PRMI
In this configuration NO glitches ( a high speed signal with an amplitude of more than 4 or 5 sigma) were found when it was locked.
Is it because I didn't use AS55 ?? or because the finesse is low ??
Also, as we have already known, the up conversion noise (#6212) showed up -- the level of the high frequency noise are sensitive to the 3 Hz motion.