andrew.lundgren@LIGO.ORG - posted 15:39, Tuesday 30 April 2019 - last comment - 02:01, Wednesday 01 May 2019(48881)
AS-A Rephasing Degraded Sensitivity
The rephasing of AS-A, since reverted, caused a big bump in h(t) from 20 to 30 Hz that I think was responsible for the drop in range by 10-15 Mpc. The rephasing (alog 48857) improves the 9 MHz buildup and the slow yaw oscillation. But the range (plot 1) drops from 115 to 105 MPc (roughly) due to a feature from 20 to 30 Hz (plot 2). It looks a bit like a scattering shelf but has a featureless spectrogram - no arches. I don't see any coherence of the new noise with the MICH_P or Y channels. I've set up a BRUCO run that might help figure out where the excess noise comes from.
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When we rephrased rf36 we changed the pointing of the beamsplitter. The extra noise looked a bit like bad A2L decoupling to me. I think maybe we should phase rf36 so the 9 MHz build ups are good and then revisit the A2L to fix the low frequency noise?
The Bruco results show big coherence with REFL_A RF45 yaw (both I and Q). The spectrum of REFL LF is elevated after the rephasing and has coherence in the same place. So A2L or touching up the alignment after the beamsplitter moves seems like it would help. Note: My first Bruco run failed (user error), so here's the new link.