sheila.dwyer@LIGO.ORG - posted 00:39, Thursday 14 February 2019 (46940)
locked on DC readout, input power glitches when increasing power
Sheila, Jamie
The reference cavity alignment has been drifting, the trans diode is around half of what it was when Peter King adjusted the alignment last week 46841 This level of transmitted power was low enough that we get an error on the ALS locking to get around this I set the low power limit on the fiber launch diode down, H1:ALS-C_FIBR_INTERNAL_DC_LOW went from 0.05 to 0.04. This allows us to lock ALS, but Rick and Peter have talked about possibly tweaking the alignment in the morning.
On Friday Jamie and Rana found that they could use some DRMI ASC, the guardian now engages MICH, PRC2 and SRC1 in DRMI. This has been working well.
We changed PIT5 settings in the guardian so that it will now be engaged with the dither line at 20.78Hz, which Jamie tested in low noise on Friday. This is working OK when we have followed all the guardian steps manually, we were a bit confused by where all the gains are. The guardian as it is worked once in ENGAGE_SOFT_LOOPS. Caution might be required when the ADS gains get reset in CHARD_BLENDS and LOWNOISE_ASC.
We lost lock three times when trying to increase power because the of a problem with the ISS, the first attached screenshot shows what this lockloss looked like when we had the ISS second loop engaged. We took the second loop engagement out of the guardian, but that didn't solve the problem which seems to show up as glitches in the first loop when we try to increase the power. The ISS diffracted power was around 3%, which it was closer to 2.2-2.4%% before the chiller problems started. We adjusted the REFSIGNAL from -2.03 to -2.05, which brought the diffracted power back, but the next time we tried to power up we still had huge glitches in the input power (3rd attachment)
We tried to lock the IMC only with the ISS on and power, that was fine.