Alexa, Sheila, Rana, Evan, Dan, Kiwamu
Today we worked on getting DRMI locked on 3F. It took us a while to get through the inital alingment sequence for various reasons, but once we did, and sorted out the WFS DC centering (Evan and Rana made some improvements to the AS A centering loop, Dan pointed out that the output matrix was mixed up), we were able to use the ASC to bring the DRMI to a reasonable build up (POP18 at 200 cnts).
We then looked at the demod phase of our 3F sensors. We tuned both 135 and 27 to miniminize the Q signal, first exciting PRM then SRM.
The best demod phases in degrees:
| PRM | SRM | |
| 27 | 85.5 | 101.8 |
| 135 | -25 |
65 |
We left 27 at 85.8 (we started at 84.8) and 135 at 65 (we started at 63). We thendouble checked the relative gain between 3F and 1F signals, they are the same as previously, and we were able to transition to 3F. (durring all of this DRMI was nice and stable, locking for up to an hour before we knocked it out with an excitation of some sort).
Since this we have made a few attempts to bring the arms in, we redid our entire inital alingment process, and after that realingned the DIFF and COMM beat notes (they haven't been realingned since the pico motor in HAM3 was moved last week). We got about 3dBm in both beatnotes.
Once we had the arms (off resonance by 1 kHz in green), we were able to lock DRMI quickly, but the build up was low. When the ASC came on, it did improve the build up but as the build up got better, we started to mode hop. This was repeated a few times. By offsetting SRCL by -800 counts, we were able to avoid this mode hopping.
We have now rung up the roll mode at 13 Hz on ETMY.
some additional info for the roll mode:
(Developing the roll mode)
In a first half an hour or so, the roll mode was not excited and therefore we could close the ALS DIFF loop relatively easily. However at some point, we saw the roll mode slowly developing on a time scale of roughly 5 or 10 minutes which eventually killed the DIFF loop supposedly due to saturation in ETM DACs. After this incident, we were never able to stably lock the DIFF loop. The loop did not stay locked for a minute. I then waited for an hour while leaving ETMY untouched with a hope that the mode settles down in the meantime. But it did not. I still had a difficulty closing the loop.
(ETMY ESD is bad)
Before we started working on the DIFF loop, we briefly checked whether the ESDs are functional or not by injecting a line in pitch at 2.13 Hz. The ETMX ESD looked fine, but the ETMY ESD was pretty bad. Even though I shook the mirror
verticallyin pitch, oplev showed the motion which was mostly dominated by a yaw motion. The yaw motion was bigger than the pitch one by more than a factor of 5. Apparently the situation is different from how we used to be a couple of weeks ago (see alog 14415). I did not try exciting it in the yaw direction this time. I believe that the ESD is the cause for ringing up the roll mode.(Some efforts did not help)
I tried two things in order to mitigate the issue. But neither worked.