kiwamu.izumi@LIGO.ORG - posted 02:52, Sunday 11 September 2016 - last comment - 21:04, Sunday 11 September 2016(29601)
Locking with the latest ring heater setting
Matt, Sheila, Stefan, Kiwamu,
We tried locking the interferometer with the latest ring heater setting (29558) tonight. The furthest point we got tonight was ANALOG_CARM.
Locking up to that point was OK with [CO2X, CO2Y] = [500 mW, 1100 mW]. However, we think CO2Y needs fine tuning to minimize the contrast defect. Once CO2Y is fine-adjusted, we wil study what is going on in the DRMI_ON_POP state.
[Matt, Jenne]
We fine tuned the CO2Y to 1.0 W. This seems to be better, since the 1.1 W was an overshoot and hurt the pitch contrast defect. Yesterday, the team started with yaw modes visible at the dark port. Today we weren't really seeing yaw problems, but we did see pitch HOMs. So, we dialed back the CO2Y, and think that we're in an okay place now.
Locking is still a struggle though :/
Last night I forgot to add that we reduced the gain of the MICH P ASC loop to avoid an instability at around 2.5 Hz in that loop. This may have been a problem because of a little extra gain, but the gain was probably too high anyway. We probably want to keep this ugf around 1.5 Hz, to be on top of the phase margin and to have a little bit of a gain hierarchy with the 8 Hz LSC loop. The gaurdian now has the digital gain reduced from 0.7 to 0.3 for MICH P.