Today we started the recovery of the interferometer by working on the West Arm.
We could see from the beginning two (one and its reflection?) white spots on the WE camera, which we could not remember (see Figure, WARM unlocked but flashing).
We looked for flashes on both B8 and, after misaligning NI, B4, without finding any, even with the "snail". We then checked the old position of WE MAR LCs and they were quite different with respect to the current ones. We recovered those and the snail could find flashes quite soon, first on the camera markers signals, then on the photodiodes.
We could easily relock the West Arm (no change in demodulation phase or anything), but the locks did not last much, and we could see a very big oscillation on the MAR correction at about 80 mHz. Fabio pointed out that the Inertial Damping of the WE was not working as expected, probably since quite a while.
Valerio had a look at the ID loop, but in the end we kept it open (Position Control) and somebody will look at it tomorrow morning.
With the West Arm locked we checked the drift control on SWEB and slowly discharged its memory; also, we re-engaged the BPC loop for the West ALS. Then also the ALS could be locked without issue.
We also did the initial tuning of FmodErr, which was quite off, without problems.
At this point the automation was put back together so that later in the evening we could do some tests of the full lock acquisition. The reverted changes are the same ones of last time, with a few minor differences:
- SQZ_MAIN is still standalone, due to the ongoing activity on squeezing;
- the automatic 6 mm setpoint for WE_Y in CARM_NULL_1F has been disabled;
- the minor changes done to ALS_NARM for the ongoing OptChar measurements have been reverted, and they will be put back again next week when we'll continue such work;
- the bypass of the DOWN condition for the Etalon loops has been removed from NARM_LOCK and put back in ITF_LOCK, since now it is in charge again.