I started to look at our locking attempts over the last two weeks, especially trying to understand our difficulty yesterday. I will write a more complete alog in the next few days, but I wanted to put this one in early so that operators can see it.
We've known for a long time that at LLO they always pull the OMC off resonance durring the CARM offset reduction, and they've told us that they can't lock if it is flashing. We know that we can lock when it is flashing here, which might be because our output faraday has better isolation.
In the two weeks of data that I looked at, we've locked DRMI 64 times, 33 of these locks resulted in low noise locks and 31 of them failed durring the acquistion prodecure. Of these 31 failures, about 9 happened as the OMC was flashing. We also had about 12 sucsesfull locking attempts where the OMC flashed. OMC flashing probably wasn't our main problem yesterday, but it can't hurt and it might help to pull the OMC off resonance durring the CARM offset reduction.
Operators: If you see that the OMC is flashing (visible on the OMC trans camera right under the AS camera on the center video screen) you can pull it off resonance by opening the OMC control screen, and moving the PZT offset slider which is in the upper right hand quadrant of the screen. Even if you don't see the OMC flashing on the camera it might not hurt to pull the PZT away from the offset it is left at, which was the offset where it was locked in the last lock. I will try to add this to guardian soon and let people know when I do.
screenshot with slider circled in a red dashed line
Evan Sheila
Here is a plot of the 24 locklosses we had from Sept 17th to Oct 2nd durring the early stages of the CARM offset reduction. The DCPD sum is shown in red while the black line shows H1:LSC-POPAIR_B_RF18_I_NORM (before the phase rotation) to help in identifying the lockloss time. You can see that in many of these locklosses the OMC was flashing right before for as we lost lock. This is probably because the AS port was flashing right before lockloss and the OMC is usually nearly on resonance.
We looked at 64 total locking attempts in which DRMI locked, 24 of these resulted locklosses in the early stages of CARM offset reduction (before the DHARD WFS are engaged). In 28 of these 64 attempts the OMC DCPD sum was above 0.3mA sometime before we start locking the OMC, so the OMC flashed in 44% of our attempts. We lost lock 16 out of 18 times that the OMC was flashing (57% of time) and 8 out of 36 times that the OMC was not flashing (22% of the time).
We will make the guardian pull the OMC off resonance before starting the acquisition sequence durring tomorow's maintence window.