Alexa, Sheila, Dan, Gabriele, Evan
In full lock, we now have the following loops closed:
- ASA45Q → dETM
- REFLA9I + REFLB9I → cETM
- REFLA9I − REFLB9I → IM4
- POPB → PRM
- −0.66 REFLA9I + REFLA45I → PR2
- ASB36Q → BS
- ASA36I → SRM pitch, ASB36I → SRM yaw
The first six of these are more or less identical to what we had last night (some of them have different gains). The SRM loops are new, and have bandwidths of 100 mHz or so, based on step response.
SRM pitch could also be accomplished with ASB36I; tonight it appeared identical to ASA36I except with opposite sign. For SRM yaw, only ASB36I was a good signal; ASA36I had a static offset which could not be affected by moving SRM. Perhaps for symmetry, we should use ASB36I for SRM pitch, as has been done in the past for DRMI+arms off resonance.
It was also possible to move SR2 and SRM so as to center the spot on AS_C. However, we have not yet tried to close a pointing loop from AS_C to SR2.
Starting around 13:06:46 UTC, we are on dc readout with the above ASC loops closed, and at 8 W input power. There does not seem to be any need to adjust optic positions by hand.
To do this, we closed our ASC loops (as above) at 2.8 W with rf readout. Then Dan slowly stepped the IMC power up to 8 W. Some 1 Hz ringing was visible in POP18 and AS90. The ringing went away after turning down the gains of the BS ASC loops by 20% or so.
It seems that the calibrated DARM strain above 1 kHz is below the GWINC 8 W curve, so this needs to be looked over before we start believing calibrated spectra, inspiral ranges, etc.
Attached is a plot of coherence between DARM and various LSC signals, and a summary of progress in the uncalibrated DARM error signal.
The DARM offset for our 8W lock is 2e-5 counts, the DCPD_SUM is about 16mA. The OMC-READOUT_SCALE factor is -6e-7, the LSC-OMC_DC_OFFSET is -1e-5.
At LLO they found that they needed to servo SR2 to ASC-AS-C QPD, with 'wide' bandwidth (1 Hz), before the AS36I WFS signal became a good one for SRM. See log entry 15840. Stabilizing the SRC axis with these loops is also credited for affecting the SRCL -> DARM coupling to make it go from being mostly non-linear to mostly linear, so that a linear cancellation of SRCL in DARM was effective.
Two more things we did last night:
When we were on resnonance and had several ASC loops closed with a very stable and good alignment, I updated the POP B offsets to center the beam before we closed the PR2 loop.
| POP B | Old | New |
| Yaw offset | -0.4 | -0.38 |
| Pitch offset | 0.3 | -0.03 |
The old offsets were set by Sheila when we had DRMI locked to a good alignment and first closed the PR2 loop.
On another note, we locked with the ETMY ESD bias off (we never feedback to ETMY), since Evan's NB plot showed we were limited by ESD DAC noise. However; this showed no improvement in the DARM noise spectra.