The goal of this shift was to recover CARM_NULL_1F.
During the shift we suffered from issues related to a few passages in the lock acquisition:
- the hand-off of DARM to B1p_56MHz failed rather frequently. We fixed it by reducing the calibration factor between the green signal and the 56 MHz signal from 1e6 to 8e5 and adjusting the demodulation phase from -1.8 to -1.6.
- the DRMI locked with a lot of difficulties, which compounded with other issues and made caused us to waste a lot of time. Reducing MICH gain by roughly 30% to 0.9 helped with this.
- the initial acquisitions of CARM_NULL_3F were difficult, as the MICH/SRCL gains appeared to be too high, but increasing them beforehand would cause an unlock soon after as the sidebands power dropped. We worked around this by reducing the gains significantly for the 3F engagement and modifying the UGF servos coding to make them more aggressive:
- we modified the PyUGF.py script in /virgoDev/Automation/PyALP/PyUGF/ by chainging the scaling factors of the gains from * 0.95/* 1.05 to *(1-step)/*(1+step) and then we set step to 0.1, to make the modification (and its future reversal) cleaner, then we stopped and started the process with no issues.
It should be noticed that CARM_NULL_3F remains a highly unstable state that only lasts long enough to go to 1F. In our case it worked 3 times.
The initial attempts to engage CARM_NULL_1F failed for what seemed to be a wrong phase for B4_56MHz. We attempted to rotate it by 45 degrees and we were lucky enough to pick the right way, yielding a successful transition for the next attempt. We then proceeded to fine tune both B4_56MHz and B1p_56MHz phases to minimize the MICH_PRCL_COUPLING and the DPHI channel respectively.
The first proper lock in CARM_NULL_1F (the first actual one was accdentally killed by human error) lasted for about 4 and a half minute (Fig.1). The sidebands power in the PRC drops by about 60% in this time.
We leave the ITF chasing CARM_NULL_1F to accumulate potentially useful data for TCS and instruct the operator to park it in locked arms before leaving at 11pm.
