Plot shows two bigh alingment changes:
1) 13 Nov 2015 start at 17:00UTC, first jump 22:00UTC, IM2 Pitch changes 46urad, IM3 pitch jumps 5urad and continues to drift another 5urad.
2) 14 Nov 2015 at 23:00, IM1 Yaw jumps 15urad, and IM4 pitch sees a jump of 50urad - this might be an alignment change.
The first jump in alignment can clearly be seen in channel 9, IM4 Trans Pitch, and ISS Second Loop QPD Yaw.
- IM2 pitch changes 605 to 565
- IM3 pitch cjanges 1948 to 1955, and keeps drifting
- IM4 Trans Pitch sees an alignment change of -0.41 to -0.2
- ISS second loop goes from 0 to -0.5
The second jump in alignment can clearly be seen in channel 2, IM4 Trans yaw, and ISS second loop pitch.
- IM1 yaw jumps from 18urad
- IM4 pitch changes 60urad
- IM4 Trans yaw changes from 0.069 to 0.189urad
- ISS second loop pitch goes from -0.18 to -0.378
Currently, Kiwamu is adjusting the alignment.
Patrick, Ed, Kiwamu,
We had a trouble locking the full interferometer today. The difficulty seems to have gone away after realigning the input pointing (i.e. IMs and MCs suspensions).
The symptom we saw was that the PRC2 PIT loop for some reason ran away in the full lock ENGAGE_ASC sequences. This resulted in a rapid degradation (on a time scale of 10 sec or so) in the power recycling gain followed by lockloss. We experienced this problem three times in a row from the beginning. By they way, we did not experience such an issue yesterday because we did not attempt to fully lock due the combination of the maintenance and high wind.
I suspected the following two things
- (1) input pointing (see Cheryl's alog above) somehow messing up the ASC sensing matrix,
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(2) the change in the modulation depth for the 45 MHz (alog 23472) impacting on the ASC sensing matrix.
- The modulation depth should be now 7 or 8% lower than it used to be. This may be critical since we derive the PRC2 error signal by linearly combining REFL9 and REFL45.
While both sounded suspicious to me, we started to address the input pointing as a first step. Since the problem seems to be gone after the realignment, we did not attempt to investigate the blending ratio between REFL9 and REFL45.
Re-alignment of the input optics
The philosophy is the same as previous processes (for example, alog 22871). Regardless of what moved the IM and MC suspensions, we move them back to the place where the OSEMs read the same value as they had been before. Specifically, I have touched MC3 YAW, IM1 YAW, IM2 PIT, IM3 PIT. However moving them back did not recover the YAW pointing on IM4_TRAS which I do not know why. On the other hand, the PIT spot position on IM4_TRANS came back to where it should be (~ 0.4 counts). I decided to move IM3 YAW to recover the pointing on IM4_TRANS (~0.05 counts nominally). I could have touched IM2 YAW instead, but I was afraied of screwing up the REFL beam and hence IM3.
After the realignment, we went through the initial alignment. The PRC2 loop seems stable so far.