stefan.ballmer@LIGO.ORG - posted 23:06, Wednesday 07 September 2016 - last comment - 23:21, Wednesday 07 September 2016(29528)
BS switched to AS_36_A at 50W
Following the suggestion of alog 29522 we switched the ASC input matrix for MICH_P and MICH_Y (the BS).
The final matrix was
MICH_P = 1.5*AS_A_36_Q_PIT + 0*AS_B_36_Q_PIT
MICH_Y = 1.5*AS_A_36_Q_YAW + 0*AS_B_36_Q_YAW
the old matrix was
MICH_P = 0.666*AS_A_36_Q_PIT + 1*AS_B_36_Q_PIT
MICH_Y = 0.666*AS_A_36_Q_YAW + 1*AS_B_36_Q_YAW
We did the ransition slowly over about 30min. Interestingly the SRM dither loop did a nice job, and the different offset in the error signal was not an issue.
We stayed at 50W a total of 40min.
While working on this input matrix switching, we saw at least locklosses that are a result of LSC_POP_A_RF45 having RF saturations. The 3rd attachment below was from a lock when Stefan was changing the input matrix a little more quickly, and we lost it during this process. The first two attachments are from our 40min lock, with different time scales.
We see that several of the RFMONs get a little high as we get close to breaking the lock, but the POP_A_RF45 is much higher than the steady-state value should be, and goes high almost a second before we lose the lock.
I didn't save any screenshots, but other locks from earlier today did not lose it due to these RF saturations, so this is definitely something that's coming up with the BS input matrix changing.
This is yet another reason that we need to revisit lowering the 45MHz modulation depth, as soon as we have a semi-stable interferometer.