Alexa, Sheila. Evan, Daniel Koji
- Angle to length coupling on ETMs. The first attached screen shot shors that when we exicte ETMX pitch or ETMY yaw with broadband noise from 20-50 Hz, we can see broadband noise in DARM. If you assume this is a linear coupling, the EMTY PUM yaw control signal explains 15% of the noise at 20 Hz, while ETMX PUM pit explains 37%.
- DHARD dominates these control signals, so we measured both pit and YAw loops and added more agressive roll offs to the existing ones. (both of these roll offs are pairs of complex poles, at 12 Hz for PiT and 10 Hz for Yaw, both are in FM9). The second attached screenshot shows the reduction in the control signal with the new roll offs engaged.The next two screenshots are OLG measurements before the new roll offs were added, for the record. Of course, another way of addressing this problem would be to adjust the coil balancing. We haven't really optimized the spot positions on the optics yet, so for now reducing the control signal seems like a better solution.
- We were able to close OMC refl, AS air and POP beam diverters in full lock. In the past attempts to close POP and AS beam divereters have broken locks.
- Evan also measured the MICH to DARM coupling and made a frequency dependent FF fitler.
- We had two lock losses tonight where the rotation stage seemed to get confused and reduce the power in the increase power state. A screen shot of the second one of these is attached.
- The other interesting thing about this lock loss was that all quad PUM current watch dogs tripped. ITMX and ETMX required a coil driver power cycle to reset.
Unfortunately, all of these promising developments happened during a lock where the ETMY ESD was tripped, untripping it breaks the lock. Evan has edited the guardian so that it will not move past ALS unles the ESD is on, so this should not happen to us again.
Sadly, the wind started gusting to 30-35 mph while we were reseting the PUM watchdogs, and is forecast to stay that way for about 24 hours. We have locked with these kind of windspeeds before, but today we are having difficulty, perhaps because the ground motion below 1 Hz was not small even before the wind started. The BRS is on at end X with broad low frequency sensor correction, however this storm seems to be mostly along the Y direction. Evan has also increased the common tidal bandwidth again (0.08 now). We've ben keeping ALS locked for 10-15 minutes.
