We first realigned the beam manually on the BPC QPDs and brought it back to its nominal setpoints. We then worked on the EIB balancing and successfully closed the loop.
From the control room, we attempted to lock the BPC, but the loop would not close. Investigations revealed that only one of the PZTs was actually responding. Further checks showed that some of the LEMO connectors on the box used to add the output resistance required for the low-pass filter had been damaged during resistance measurements performed a few weeks ago. Roberto repaired it, and all four PZTs are now responding normally.
However, the manual alignment performed in the morning had been carried out with incorrect PZT settings, leaving the beam significantly displaced from its nominal position. We will need to return to the laser lab tomorrow to repeat the manual alignment.
We also worked on the alignment of the IMC cavity. We managed to obtain flashes up to 5–6 W, but we have not yet relocked the cavity. This work will continue once the BPC loop is closed.
For the night, the PMC was left scanning (with a 1.5 V offset applied to its error signal), and the mirror at its output was flipped.
Work will resume tomorrow.
