Alexa, Sheila, Dan, Kiwamu
I was about to post the alog below, when we decided to go back to 1 Watt since everything else we have tried to get DRMI stable at 10 Watts has failed. At 1 Watt we had no mode hopping issues, we aquire lock within 10 minutes or less, and it is stable once we lock. This sounds like a familiar story.....
Right now we are trying to transition to 3F, we didn't suceed at 1 Watt so we are now trying at 2.9 Watts.
The old, sad alog:
Today we tried to get PRMI to be stable again. Our working theory is that we are having these mode hopping problems beause of some bad alignment. Our intial alingment scheme right now doesn't fix the alingment of PR3, so we have tried various methods to recover this alingment to a time when we had more stable locking.
- We have added states to the ISC_DOF guardian (what we are now calling the guardian we have been using for inital alingment) that align PR3 using a servo on the GigE camera on ISCT1. It seems to work, we have the current position as the target right now, but this obviously isn't optimal. Once we find the good alingment we should both center the POP QPDs and mark the location of the ALS X beam
- The most sucsessfull method we tried was based on trending old offsets, locking the IR to the X arm with refl wfs actuating on IM4 +PR2 to keep the input beam aligned down the X arm while we moved PR3 a few microradians. We then locked PRX and used the refl wfs to actuate on PRM. We found that our PRX +wfs don't yeild a repeatable alingment of PRM. We tried to walk ourselves towards the old alignment using this method, but found that our best PRMI build up was in the other direction. The result We were able to get the build up in PRMI better (we went from about 150 counts in POP 18 at max to almost 200 (perviously our best PRMI build up was 220), however we are still mode hopping. Until the last two days, we hadn't seem this mode hopping in PRMI, just DRMI. A video is attached, at the end of the video we drop the lock.
- We tried some other methods, like simply restoring to our old offsets, and we tried locking the input beam alignment to the X arm while we move PR3 to get the beam spots on the POP sled back to the position they were at when we had stable DRMI late last week. (both of these methods were complete failures, resulting in very low or no flashes in PRMI)
We also got a DRMI lock, which lasted only a few minutes, and dropped at 1:53:07 october 18 UTC, that is the second video attached. Our big victory today was that Alexa killed the fly that has been hanging out in the control room.
We tried increasing the input power to 4W; at this point DRMI was already unstable.
Alexa, Dan, Kiwamu
Tried several times of the 3f locking, but was not so successful because the SRCL loop did not like to be locked with the 3fs. Only once, we were able to transition to all the 3fs at 2.7 W. At this ponint the input element was 1, 2, 5 for PRCL, MICH and SRCL loops.
We started checking the demod phases. Surprisingly, it seems that the good demod phase for RF135 has changed from that of 10 W by more than 45 deg. MICH and SRCL show up mostly in the opposite quadrature. We should do more precise and careful adjustment for this
When we were at 2.7W and locked on 3f with MICH and PRCL, I measured the open loop transfer functions. The UGF and phase margin for PRCL has been the same as before (UGF of ~70Hz, with 40 deg phase margin). However, the UGF for MICH was too low, ~ 2.5 Hz.