Dan, Cheryl, Evan
Sometime after 6 am local yesterday, we lost the ability to have stable locks with full input power.
It's not clear what about the interferometer changed, but the symptom again seems to be a slow drift of the AS36→SRM yaw loop which causes a sudden lockloss after a few minutes at full power.
In the end we simply retuned the input matrix elements for this loop in order to keep AS90 and POP90 from drifting downward at high power.
Before, the matrix elements were
ASA36I→SRC1: −3
ASB36I→SRC1: +1,
and now they are
ASA36I→SRC1: −3
ASB36I→SRC1: +0.5.
This combination was not chosen particularly carefully, but it is good enough to get to high power. We may want to see if there is a better combination.
The attachment shows the behavior of the four AS36 signals during power up and the subsequent full-power lock.
Although we've recovered high-power operation, there is severe scattering causing shelves reaching up past 100 Hz.
I checked the velocity of OM1, OM2, OM3 and OMC measured by BOSEMs just to make sure that these are not shaken badly, and they are not.
In the first attachment, thicker lines are from this morning, thinner ones are from four days ago. All of the plots are already multiplied with 2*pi*f in dtt calibration, so these are velocity.
Doesn't look like these are moving more than before.
Second attachment shows non-stationary low frequency thing from this morning.
