Sheila, Craig, Cheryl
Tonight we are stable at 25 Watts, without the ISS 3rd loop on and no SRM control. The range is just below 70 Mpc, and the spectrum seems non stationary with lots of loud glitches which aren't due to anything much that we have been doing.
There is a broad peak around 60Hz, which is not something I've seen before, Craig found there is coherence with LSC signals there. As expected we have a lot of noise from CHARD below 30 Hz. We decided to try blending with the transmon QPDs. We started with a simple blend, two poles at 4 Hz for the refl WFS and a complimentary filter for the QPDs. This reduced the noise (and the coherence) but we still need to improve this a bit, probably with a . We simply used the combination of TMS QPDs that is orthogonal to what we are using for the soft loops, so we might be able to find a combination that has better SNR for CHARD than what we are currently using. Once the coherence with CHARD yaw was reduced we have more coherence with pit, so blending this will probably be one of our next jobs. The current settings are in the screenshot.
The IFO has been basically undisturbed since 6:05 UTC, but we aren't easily able to hit the intent button, maybe because of old excitations...
S. Dwyer, C. Cahillane We took a reference spectrum before turning on the blending of the CHARD Y error signal and after. (Plot 1) You can see where we win at about 20 Hz. Now that we have damped CHARD yaw noise at low frequency, we have CHARD pitch noise... Also, Plot 2 shows coherence between MICH, PRCL, and SRCL to DARM, particularly around 60 Hz.
