Today we have had some difficulties with alignment in the process of recovering the IFO.
This morning we moved ETMX by 20 urad in yaw, Patrick checked trends and the top mass osems roughly agree with the alingment sliders that we moved by about 20 urad, while the optical lever indicates that this was moving the test mass back to the position it was in last time we were locking, on August 1st.
We also saw that even after doing initial alingment twice, the arms atill had a large relative misliagnment which caused a low recycling gain and therefore a lower cam offset than expected while CARM is locked which cause random locklosses at different points. Earlier tonight we we seeing a 5% drop in the refl power when the arm transmission was at 5 times the single arm power, while the same arm transmitted power level on August 1st coresponded to only a 1% drop in reflected power. Koji and Stefan worked on solving this problem, so I will leave it to them to log their solution.
Koji, Stefan
We co-aligned the y-arm for IR and green by comanding the guardian in an y-arm IR lock, and simultaneously engaging the green arm alignment. Then we moved the ITM green camera set point around, and kept the IR maximized with the BS. THis resulted in a nice co-alignment.
WIth that setting we had much less truble during the CARM reduction sequence, but once we were on resonance, we kept loosing the lock in a fast transient. Our guess is that there is a problem with the CARM loop, but we didn't have the energy to check that.
At least the fast sutter is reliable triggering on every lock-loss.